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Little Help With Repair and Guidance

02/06/2013 5:01 PM

I had been using my Motorola S1303a Power supply circa 1975 (0 to 18 V, 0 to 40 A) when I started driving too much potential my curent meter pegged rather quickly and POP went something. The potential gets pegged some times, and other times it gets stuck about ten Volts while still driving a rather week curent, say 3-5 amperes. At that point I have no controle with either controle nobs....

Anyway I would like to repair it myself, Problem is I can't locate a repair manual, schmetics or a flow chart. basically nothing..... I cant see any damage to any components boards or connections..... I can r&r everything one at a time but there must be a correct protocol of some sort to follow...

Little help please!

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#1

Re: Little Help With Repair and Guidance

02/06/2013 5:29 PM
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#5
In reply to #1

Re: Little Help With Repair and Guidance

02/07/2013 2:14 PM

Yes this is it by the pic. I will follow all the links and see if your input search is what I have been looking for.

Thanks ahead of time.

Zane

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#10
In reply to #1

Re: Little Help With Repair and Guidance

02/07/2013 5:50 PM

Thanks for looking SolarEagle I found those also the other day.

I will do my testing and come up with some other questions.....

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#2

Re: Little Help With Repair and Guidance

02/06/2013 6:15 PM

If it 'sort of' works and you can't find schematics, etc., I would trying replacing the potentiometers first. They are mechanical in nature and prone to failure. The 'Pop' concerns me, but pot's are pretty cheap. Have you looked for blown fuses?

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#6
In reply to #2

Re: Little Help With Repair and Guidance

02/07/2013 2:21 PM

It has a slow blow fuse, looks different than a regular fuse ( coper wire leads to a square rectangle link attached to a spring then into the other end) it says BUS MDL 15. Looks still intact.

I tested Both Pots for steady resistances and complete movement throughout the scale. They seem perfect.

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#3

Re: Little Help With Repair and Guidance

02/06/2013 8:37 PM

A good bet would be to replace the electrolytic capacitors. They do have a finite life time, and 30 some years is pretty old for them.

I've had several power supplies with that problem.

Dave

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#7
In reply to #3

Re: Little Help With Repair and Guidance

02/07/2013 4:34 PM

It has a small number of the flat type caps,(are these the electrolytic caps)?, six variable pots that are painted like the paint is used so depict that have been set. Looks like five small transistors, These are set on the race track (very simple), it has two large heat sinks with a fan attached there are four large Mosfet round things, Not too sure... with three wires only two hooked up" and two others with two wires on that "these may be large diods" but these go to the two heat censors that controle the fan.... It has only one small diode on the race track. It also has one IC. the last important thing I can see is the Printed circuit board multi-bus connectors what looks like green corrosion on the all of the contacts on both harnesses.

Then a large 33000 uf 65 volt monster cap, a hand full of small round caps, a baby transformer and "the large one".

Would a picture or a video help? I need this puppy running like yesterday...

I've got science to do..... busy me.. Hopefully I am still a good student.

ok,ok I know I am going to have to learn something on my own.

If I am not mistaken can everything be troubleshooted while hooked up except resistors?

This thing looks like a walk in the park. Can I measure all of the caps in place?.

No more questions from me. sorry.

Zane

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#12
In reply to #7

Re: Little Help With Repair and Guidance

02/07/2013 11:59 PM

Looks like a dog's breakfast in there.

With all respect intended, I'm more than a little concerned that you want to fix this but don't know the difference between electrolytic and ceramic capacitors.

Bite the bullet and get yourself a new one, they're not expensive these days and will likely be more stable and reliable to boot.

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#18
In reply to #12

Re: Little Help With Repair and Guidance

02/08/2013 11:34 AM

yes, you are right a bit confused about why I can't remember what caps are what. I probably will get that newer power supply if I can't get to the checkered flag with this one, but like many people I have an obligation that tells me to figure something out. I must start learning some, You see I have been tearing things apart for years and years saving parts I thought were really cool. How foolish it seems I'm divulging my curiosities but that is me..... I have two scopes to fix and a signal generator as well. if I don't get with the program and accomplish something I will feel like *^\/ % O! A FOOL. for dreaming about something and not even trying.

Thanks for the reality check.

Zane

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#15
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Re: Little Help With Repair and Guidance

02/08/2013 2:30 AM

Ok. Definitely change all the axial electrolytic caps. Take a close careful look at all the diodes. The big metal devices on the heatsinks are all probably diodes. Look for any oily residue or paper around the caps. Check the metal tops on the big diodes on the heatsinks, one may be popped off. Your meter likely has a diode check function, use it to check all the diodes. Be sure to isolate one lead of each diode first! The schematic for this guy is fairly simple and very generic. Get the number off the IC, if you look it up you'll almost certainly be able to find application notes from the maker. If not, there are several good circuit source books. One will likely have a schematic almost identical to your supply. Hopefully you won't need them, because either the caps or one of the diodes is bad and replacing them will fix her up! You should probably replace the big caps as well. Over time the electrolyte tends to dry out, ruining them.

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#61
In reply to #15

Re: Little Help With Repair and Guidance

02/16/2013 4:43 PM

I have good hands and this sounds like easy enough information to follow. Cap replacement and Checking diodes. I can do that.

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#62
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Re: Little Help With Repair and Guidance

02/16/2013 6:13 PM

"I have good hands and this sounds like easy enough information to follow. Cap replacement and Checking diodes. I can do that.'

As long as you understand what forward and reversed biasing conditions means on a diode or for a P-N junction of a semiconductor, as well as the knowledge on how to implement those limiting conditions while conducting your tests, then I agree with your assessment.. it is really a very basic and easy test to do that also goes a long way into the proper dynamic operation of those devices!

Good luck!

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#64
In reply to #62

Re: Little Help With Repair and Guidance

02/17/2013 3:55 PM

youch, i'm not qualified yet.

I wanna be an A... Parts changer

I wanna be a B.... Technician.

I will change caps first then Diodes and then we'll see. I can test Caps and Diodes and some Transistors with the meters I have now.

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#66
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Re: Little Help With Repair and Guidance

02/17/2013 5:51 PM

Since you can easily identify each component(s), it will help you a lot to try tracing and labeling how each device are interconnected. Starting from how the power transformer is wired, up to the heatsinks where those 2N3055 are mounted.. Slowly going by this approach you can start to have an understanding or expectations how a component functions, or how the circuit should behave? Using what you observed and results of your tests as reference when asking questions online will be very helpful!

Example:

Those two "42" are SCRs. They may be serving as fuse blowers in a crowbar ckt. configuration. The base is the cathode part of the SCR, that when triggered by a predetermined abnormal level of current will remove the power to save those transistors from self destruction! Look for some hidden fuses that may have been blown open!

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#68
In reply to #66

Re: Little Help With Repair and Guidance

02/18/2013 5:36 PM

Thank you the analysis continues.

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#69
In reply to #15

Re: Little Help With Repair and Guidance

02/23/2013 5:53 PM

Back in the lab again,

Again I have looked all over to find some information about this IC just to see if I could get a clear idea about how this circuit is suppose to operate. I have two wires that come from the major components that control how the transistors are supposed to switch. I just cannot find what I think should be there.

methodologically I want to visualize or measure what should be happening but I.m unsure.

On the race track I find Ratelco on the back side as seen in another picture (already posted) that doesn't seem to lead to a grip of details either.

By the way i have found a seller willing to sell this Powertron PX80-125 for 299.00

This is much closer to what I really need anyway.

The education is highly valuable and I do appreciate everyones help

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#70
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Re: Little Help With Repair and Guidance

02/23/2013 9:10 PM

As you try, (hopefully), to trace the circuit and draw some sort of wiring connections between the 'major' components as I previously suggested, you can at this point represent the circuit board as just a "square or black box" in your diagram.

Later on as you trace individual wires, connecting individual major components together from the (power transformer and on), including any connections going to the 'black box'. It will be a slow process but once done, It will give you a better picture and us some idea on what purpose the ckt. brd.(black box) serves in the overall ckt. Depending on what goes in/out to the 'box', it will give us some indications on what function(s) it serves. It is very possible for that board to contain some controlling element, current sensing /limiter, or even an osc. that will control how the SCR is triggered to conduction?

In short what I basically want you to do is slowly /carefully try to reverse engineer that power supply circuitry. It will be a good learning exercise since you don't have any schematic diagram.. It is not gonna be hard, the ckt. board is only a one layer board w/ few components on it.. good luck!

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#16
In reply to #7

Re: Little Help With Repair and Guidance

02/08/2013 9:42 AM

As shown in your picture, you need to be able to identify and locate each component before you can do any test or replace any..

As far as I can see from your pictures;

1. the circuit board contain some tubular "tantalum" and round disk type "mica" capacitors which are pretty reliable. Some resistors and small trimming potentiometers that normally used for fine tuning adjustments.. I doubt any problem wiith this board, so I would advise to leave them for last to test if need be?

2. Next shown are components mounted on aluminum heat sinks. The problem may be around here since these carry most of the power.. Here locate fo some "temperature dependent protective device", as it appears to me, it is a bi-metallic type thermostat.. It is a round flatly mounted or glued onto the heat sink with two wires. Normally they should be short-circuit or normally closed device during operation and will be open-circuit when it sensed hight temp. Also notice evenly spaced tiny holes in the aluminum channels where you will find transistor terminals are coming thru. You'll need to un-solder the wire connections (open connections) from these devices to test each of them properly!

3. The last two pictures is for the main power supply. The big square unit seating on the chassis is your full bridge rectifier. The big cylindrical capacitors are your filter caps which at this time either leaky or have sprung leaks? You need to replace them all with the same or better capacity! The other bigger potentiometers should still be okay?

For your safety, before you touch or conduct any test,

1. be sure the unit is unplug from the wall then short all terminals of the big filter caps to ground /chassis. (put a jumper wire to the chassis).

2. You are familiar on how each device behaves and normal functions..

Good luck!

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#4

Re: Little Help With Repair and Guidance

02/07/2013 4:57 AM

Previous 2 posts are V good.
I'd also suggest checking/reflowing joints, & wiring around any terminals, connectors and power components (and range switches if it has them)
Check out any feed back and sensing components/paths.

Look out for any obvious test points and try to get a scope on it before/after/during a failure mode.
Hate to say it but without a cct diagram it's pretty much a stab in the dark.
At the risk of mixing my metaphors...
These days I won't get out of bed without a circuit diagram.
Del

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#8

Re: Little Help With Repair and Guidance

02/07/2013 4:49 PM

Ok if I get brave enough I'll probe around with my scope to see if a signal stops or is off my highest grid. Look at the frequencies and see if I can find the faulted component.

that is after I clean the contacts and re-secure all the joints. measure the caps and check the resistance on the set resistors.

I guess that is what I will do. anything I should be cautious about?

Well besides the jolt from the 120 or the big cap?

Is that about it?

Zane

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#53
In reply to #8

Re: Little Help With Repair and Guidance

02/11/2013 7:56 PM

You may already do this, but just in case you do not: working one handed is a good habit to get into.

Getting shocked on one hand will still hurt enough you won't feel like you missed out, but it does lessen the likelihood of the circuit you form directing much current across you heart.

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#9

Re: Little Help With Repair and Guidance

02/07/2013 5:24 PM

Blimey that's 'state of the Ark' technology!
I would n't trust any of the capacitors in cans. The flat disc ceramics are prob ok.
Those carbon resistors can crack up too.
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#11

Re: Little Help With Repair and Guidance

02/07/2013 11:35 PM

Replace the small aluminum electrolytic caps. I'll bet your problem will go away at that point.

But I'd replace the large electrolytics too and clean up the hardware. For the screws on the big caps put a little Locktite 222 on the threads.

Typical regulation, ripple issue I had on some Sorenson power supplies.

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#13

Re: Little Help With Repair and Guidance

02/08/2013 12:09 AM

You said something went "pop". Is there a burnt smell? That usually indicates the partys over.

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#17
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Re: Little Help With Repair and Guidance

02/08/2013 11:17 AM

No there was no smell evident. the primary cooling fan was on at low speed.

I had been running it for approx 2.5 hours and using just enough power to cycle the secondary speed control on at the same time, "that same fan".

I was testing varying loads and adjusting the Pots at random intervals. At the time it popped it was at low current steady; fan running, Then I just turned the Potential Pot maybe just a little abruptly higher, nearly full range", and the amperes gauge very quickly pegged and it was over then.

Probably the smell if any was blown away. couldn't say?

Lots of great advice here.

Thanks

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#14

Re: Little Help With Repair and Guidance

02/08/2013 1:52 AM

When you take into account the time to fix, the lost hours on your 'real' work, and the likelihood another problem will manifest itself soon... Is this too much to pay? (Ball park figure, other suppliers available -"power supply 0-40a")

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#20
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Re: Little Help With Repair and Guidance

02/08/2013 12:11 PM

I bought this power supply because it is about 1/8 of what I intend to be using (huge dream) anyway I cant spend much cash on my lab at this time so I will follow the good advise I am getting here to get the job done.

I find the link has some confusing numbers. Yes it does advertise 40A but it also says The current is 14A. the banana plugs seem to be too small to carry the current my project demands. I have two sets of banana sizes on this power supply one is fed with 18 to 32 ga silver coated wires and the 40A leads are fed with 8 ga silver coated wires.

This is not nearly enough for my future lab work so I will tend to shy away.

Thank you for your comment.

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#19

Re: Little Help With Repair and Guidance

02/08/2013 11:52 AM

I though the supply was still working, just unstable.

so, it's also possible that some of the pass transistors bit the dust, They are probably pairs of tranisistor resistor in series and then a parallel combination. Check the temperature of the transistors.

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#21
In reply to #19

Re: Little Help With Repair and Guidance

02/08/2013 12:14 PM

I can do that!

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#22
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Re: Little Help With Repair and Guidance

02/08/2013 1:59 PM

Or the bi-metalic thermostat has openned up due to overheating, thereby making the power supply to work half way working only? He needs to check the thermostat for continuity.. it may just be the only one causing the problem in the circuit?

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#24
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Re: Little Help With Repair and Guidance

02/08/2013 2:54 PM

I can do that too.

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#23

Update

02/08/2013 2:47 PM

I fired it up again. its all open and running.

The potential is adjustable between 14-16 Volts, where the current is floating with the potential pot 0-1 amper, both are steady. The Ampers pot will not, nor did it ever adjust to low amps. (By the way this is the first time I have used any Power supply including this one).

Couldn't find too much with the scope, sign wave, & bridged signal, on the big transformer. thats it.

The issue seems to be one complete side of the heat sink is not working at all.

I have been pulling a load with it at these measurements and only one side is warmed up. The other side is still cold.

The secondary fan circuit has kicked in and running constantly. seems like I may over heat it/ No it is at a constant 135 F and 65 F on the cold side.

That is the power transistors and resistors series parallel circuit as described before.

I have turned off the Stand by circuit which normally cuts all power to the leads and after about 13 min the secondary fan power turned off.

This is the Funky thing; (probably because one of the transistors is shorted out) I have this weird 18 volts going to the load when the standby circuit switch is off. (Reads zero current), (The meter says 13.5 volts) Then when I disconnect the Load manually the potential meter pegs until something overloads/bleeds off and then the Voltage very slowly drops off to nothing? Humm

another anomaly is this...

when the Load cable (Test lead) is removed from work the Volt meter immediately pegs after 12 seconds it slowly drops off to zero taking 24 seconds then pegs again and starts that cycle again?. Yea its redundant but I had to double check<3

These strange occurrences are probably results from the capacitor still being charged from a broken transistor "shorting and bleeding to the smoothing cap. That is just a guess.

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#25
In reply to #23

Re: Update

02/08/2013 3:57 PM

The thermostatic switches should be normally closed or shorted when the heatsinks are cold, verifiable by a continuity test, or by temporary jumping its leads together when circuit is powered. It function as a protective device in case there is an abnormal rise in temperature of the heatsink. Behavior is such that it opens up at certain high temp and resets back to close condition when temperature normalized.

Also it is normal for the stored capacitor energy to be discharged slowly as observed during the power down. This normal energy decay is done through a bleeder resistor for regulation and added safety.

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#26
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Re: Update

02/08/2013 4:40 PM

Thermostatic switches can 'lock' open. They can be made from a slightly domed bi-metalic disc, which pops the other way when too hot. If overheated suddenly, they can stay in the open position until manually reset. I have not seen any of them in the pics (post 7).

The third & fourth pics show the heatsinks with wiring to two resistors and two separate wires to the sensors. I would suspect the one on the heatsink which stays cold is not functioning, or has bad connections / components.

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#27
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Re: Update

02/08/2013 6:15 PM

Look again on the pictures depicting the aluminum heatsinks and where the transistors are mounted. Concentrating at the picture on the left, On the extreme left (near the edge of the heatsink) is where one of the thermostat(s) is mounted and can be found.

Depending on the needs and circuit application, the type of thermostatic switch used can be either normally closed or normally open. Based on my experience, most commonly used is the normally closed type.. since its application often requires interrupting current flow or opening a circuit path once an abnormal temperature rise and condition has been detected /sensed. I won't be surprised if one is mounted on every heatsink.

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#30
In reply to #27

Re: Update

02/08/2013 7:19 PM

What is not obvious to me is whether the sensor is straight on/off, or analogue. The two-speed fan would suggest that it is analogue, and that there is another part of the circuitry which controls fan speed & cut-out.

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#32
In reply to #30

Re: Update

02/08/2013 8:14 PM

From the specifications and pictures provided, it seems to be a regular analog type of power supply. Whether equipt with a crowbar type of protective ckt. is another question? With no schematic on hand, the best that can be done is speculate..and guess?

Since it is halfway functional, the approach I can suggest to the OP is do a systematic approach of testing. Isolate the working side and concentrate on the non-working side. Comparing physical and electrical conditions and components behaviors between similar types of devices is a way, since he is quite observant and willing to learn.

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#31
In reply to #26

Re: Update

02/08/2013 8:07 PM

These are the only things that I thought were Two thermo switches but are fooling me. the one on the other side is working the fan motor and it goes from about 45V ac on low to nada Vac on high fan operation. on Low operation the continuity tester will turn the high fan on. The green thing has no continuity when on high and no ac going through it then. but it does have Ground on one terminal from the mains, and the placement screw that goes through it to hold it down has the Hot 120V ac.? This is the Green thing going through the fan transformer that is hooked up to mains ground and is attached to and is grounding to the heat sink lower bracket that floats on a plastic bracket from the top of the outer case. causing sparks when using my continuity tester. Ouch bulbs gone....

the round thing on this side with the small green wire is on or closed all the times, I find no variations with its operation. the green wire goes to the circuit board.

These two white 42 things are heavy lugged to the heat sink that is cold

Ok I was mistaken about the DC voltage going to the heat sink. it is actually 120V AC hitting the heat sinks.

I know that must be a clue!

OMG I'm glad I have been cautious. I don't like getting bit.

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#33
In reply to #31

Re: Update

02/08/2013 8:29 PM

Now we're a little bit moving forward with the addition of these two components. If these two round things have 2 terminals on one side, a small and a bit bigger terminal, these components is probably an SCR that belongs to the thyristor family. The smaller terminal will be the "gate", the bigger one is the "anode", with the mounted body being the "cathode". You need to retrieve the part number to be sure..

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#63
In reply to #33

Re: Update

02/16/2013 8:32 PM

Alright these two# 42 things have an "s" in a box then 7145 Then a picture of a diode symbol

Think your right

Next letters and numbers are D367 AC

The small lug goes to a resistor brn Grn Blk Silver; .15 ohm On each of the two heat sinks and to each of the two # 42 SCR's in turn are fed via the small yellow wires that lead to the race track where they are combined at the terminal and these go directly to the little small thumbnail transformer.

The SCR's are bolted with a heavy lug to the heat sink mounting metal, That metal is directly connected to the main transformer secondary HOT I propose AC.

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#34
In reply to #31

Re: Update

02/09/2013 3:36 AM

It is unusual to find a heatsink on the live side. It may be a case of swapped live/neutral. Is there a separate ground wire?

Are the '42's on each heatsink, or only on the cold one? If circuit is duplicated, then comparisons of voltages & resistances will likely point to the faulty component.

Did the fan come on slow speed on start-up when it was working correctly?

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#65
In reply to #34

Re: Update

02/17/2013 5:34 PM

The 42's are Not contacting the heat sinks, nor are they physically touching them either. they are mounted to the insulated bases that the heat sinks are insulated from but mounted to.

The 42's are directly connected to this blk wire screwed to the mounting bracket that is directly going into the trsfo secondary winding.

yes the fan did come on slow speed when it was working right.

It is unusual to find a heatsink on the live side. It may be a case of swapped live/neutral. Is there a separate ground wire?

I am dissecting the wires to see how I found the 120v ac around the Heat sinks. I think I was using the heat sink ground and referencing the fan motor voltages "so probably a bad Negative reference".

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#67
In reply to #65

Re: Update

02/17/2013 6:04 PM

Those are NOT insulated base and that is a normally open ckt!! The base with the stud mounting is supposed to be the cathode end of the SCR. If the mounting were not isolated, means that when they fire, conducting or triggered, the Anode end will be on the same potential as the heatsink. So the heatsink is live and floating from the ground plane.. Follow the black wire going to the transformer... see if there is any fuse inbetween before the secondary windings?

Be safe!

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#28

update 2

02/08/2013 6:30 PM

Ok so i started testing the voltages when full power (standby On) and Off, on both sides of the heat sink. everything is voltage wise the same. when the power bleeds off everything on each side bleeds off. when the spike returns it is the same everywhere. both fan controllers seem to be working, ie. when the main power switch is turned on the primary fan turns on. When the heat sink components get about 112F or so the secondary fan turns on, that also turns off about the same temp.

As I step back. I was using ground from the Load side. so maybe that will give me a false reading.

I'll go recheck.

Ok looks like I must use a circuit ground. thats good. but it turns out both heat sinks are electrically hot. DC about 23V sounds strange to me.

Also every component there is hot between 17 to 19 volts on both heat sinks except two components.

The green thing was running at 95F no dc voltage readings?

The top of the green thing goes directly to mains ground. there is no continuity through the green thing and neither is there any continuity through the thing on the heat sink.

The fan next to the green thing is spinning and it has a combined transformer below it the mains ground goes through this....it has about 43V ac going through it when the power switch is on and fan turning....

Humm still stumped?

I not made any modifications yet.

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#29

Re: Little Help With Repair and Guidance

02/08/2013 7:07 PM

The green thing to the far left is a power resistor and the thrmo switch is wired across it. Bet dollars to donuts that at high temp, the thermo switch closes. The thermo-switch and the resistor effectively make a two speed fan.

The next test I think you should do is measure the B-E voltage of the transistors. That would be the voltage between the two pins.

0V would not be good. Something around 0.6 V would be OK.

Warning: The transistors used in this arrangement are better being matched in gain if they need to be replaced. Don't worry, you can build something simple to measure the gain. It may mean you will have to buy 10 transistors to get one that is close. Within 10-20%, at least.

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#35
In reply to #29

Re: Little Help With Repair and Guidance

02/09/2013 1:31 PM

You Got it. The green thing has 120v ac on one side and 80v ac on the other. that thermo switch does close and spin the fan faster.

"question", why does the bolt that holds down the power resistor have about 48v ac on it I am using mains ground for my test meter and the scope reads a sign wave that is broken slightly on the leading slope of the positive slope and another break on the trailing slope of the negative slope. with a 10 * probe it shows that same 50v ac peak to peak?

There are three transistors on one Heat sink and two on the other, two sets match.

on the two side (hot side), between the two B-E measures 1.2 v +dc the two matching on the other side read 1.4 +dc the third one on that side reads zero.

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#36
In reply to #35

Re: Little Help With Repair and Guidance

02/09/2013 3:53 PM

The bolt should not have any potential on it. Let's skip for now.

The zero volt is bad. Check the emitter resistor compared to the other ones. They may be extremely low values and very difficult to check UNLESS you can build something to control the current through it and the voltage across it.

If you remove the transistor, hopefully you will find the B-E junction shorted with an ohmmeter.

I'd actually, like you to measure the gain of a good transistor and replace both the bad transistor and emitter resistor. What's the transistor type number? The idea would be to inject some base current and measure some collector current thus determining gain.

Matching, basically requires buying a batch and selecting. I'm on the east coast and I could do it for you. i.e. send me a good one and a batch of new ones and I'll write the gains on each of the transistors and send them back.

A 9V battery and a 1.5 V battery and a couple of resistors and a voltmeter. The datasheet for the transistor would help.

----

The resistor thing may be problematic. There may actually be noting wrong, but I can think of where problems can be based on experienece.

What I do suspect, is an EMI filter and/or poor grounding somewhere. An outlet strip with a ground lifted. The ground connection between the scope and the power supply.

Do measure the AC voltage between both of the chassis. Close to 1/2 the value of the AC line voltage brings up issues of bad grounds and EMI filters.

I had one issue where 430 outlets really needed to be replaced, but they said no. They did replace outlets on sensitive equipment and then as sensitive equipment were put in the other ares, the outlets were tested. It was a tough test: An outlet tester that checked for ground resistance was plugged in one of the duplex receptacles and a dud plug into the other. The dud plug was moved and the ground would lift. It was confirmed by diss assembly.

A bad ground in an outlet strip did the same thing with the ~1/2 line voltage between the two grounds. I don't want to explain that one unless I have to.

-->If the above doesn't reveal any problems continue on this line:

I expect no problems with the resistor, but clean off the dust. Check again. See if you can remove the wires from the other side of the resistor without disturbing the resistor. Check resistance from the other wires to ground with both leads disconnected far from the resistor. I suspect no problems.

--

For a full rebuild, the caps should be replaced.

__

The transistor with 0V can be removed. Current capability will be reduced and it's best to replace it ASAP. The transistor generally has a mica insulator under the bottom if it. They require heat sink grease. White stuff that doesn't like to come off your hands easily. Silpads don't require grease. They have some give to them, like a rubber gasket. If you disconnect, be careful and make sure the leads can't short to anything.

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#37
In reply to #36

Re: Little Help With Repair and Guidance

02/09/2013 6:35 PM

Thanks, I'm on your mission.

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#38
In reply to #36

Re: Little Help With Repair and Guidance

02/10/2013 11:59 AM

Ok, a couple of points here first then questions....

you are talking about the 4 wire Kelvin resistance test right. I can put together one of these devices.... This test device, I guess can be used for many other tests I imagine..

Then if my imagination is accurate your proposition that all transistors should be very close to identical is imperative. Thus explaining why they have marked the back of the transistors with various numbers to correlate a balanced circuit? or something like that.

I did check the Ground and neutral circuit from the mains and they are connected. well I do not have a ground meter per say but I do have a device that says the ground and neutral are hooked up. i do suspect a grounding error possibility with a flat cap that is hooked to the + lug to the case of the unit that may have been floating?

Caused by loose case bolts that have been overtightened. I'll fix that as well.

Lets go on.

good hot side 1

Good hot side 2

Good cold side 1

Good cold side 2

This is my reference with the bad Transistor and the next part in series.

I don't know why they have 40 here and a different transistor.

If its bad its bad. so deciding if the series component to the reference photo is off target (I don't know if the gain is obviously "set in stone" or combined with the following component in series.). a bit complicated...

I'll have the resistance measurements pretty soon.

Thanks for the journey.

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#51
In reply to #38

Re: Little Help With Repair and Guidance

02/11/2013 7:47 PM

Pictures labeled "Good Hot side 1" and "Good Cold side 1" are of the same actual component.

.

Similarly "Good Hot side 2" and "Good Cold side 2" are pictures of the same installed piece.

.

Was this intentional and I'm just misunderstanding the intent? Or was this a photo mixup?

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#55
In reply to #51

Re: Little Help With Repair and Guidance

02/12/2013 11:15 AM

Not intending to mislead anyone. I thought I had only one possible error. But obviously there were more. I move all my pictures from the camera to a temporary folder then to a designated file for archives and finally to an archive place I can add any compilation I may wish in the future.

No duplicates or misleading picture or representations were intended. just trouble on my part figuring out an adequate name for the various photos.

When i got ready to post the message I noticed a picture with the same name so I deleted one. I guess it was the wrong one.

Thanks for noticing.

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#56
In reply to #55

Re: Little Help With Repair and Guidance

02/12/2013 11:31 AM

You are welcome.

BTW I didn't think you were trying to mislead. I just thought it was either a mistake, or I just couldn't grasp what you were trying to convey.

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#44
In reply to #36

Re: Little Help With Repair and Guidance

02/10/2013 7:31 PM

The B-E junction has 14.k resistance, "give or take" it just keeps getting more and more the longer I leave the meter on it and also changes when I test each leg to the housing of the transistor.

Between one of the legs to the housing it show 13.6k resistance?

Between the other leg it shows over 300m ohms give or take?

Incorrigible transistor! It keeps changing... when I get the thing all zeroed out by grounding both legs together and to the base of the unit. I can get steady readings but after I go through each one then test again it gets all weird on me.

Now between B-E it reads 278m ohms?

If this is normal I won't sweat it.

On second thought I will pull out another and test it..

Thanks for all the input.

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#39

Re: Little Help With Repair and Guidance

02/10/2013 2:28 PM

The 2n3055 transistor used to be very common. The gains range from 20 to 50. http://www.futurlec.com/Transistors/2N3055.shtml Thus this one probably had a gain of 40 and the others 35. It also means that it took a tiny bit more of the share of the current. It also means you have to buy a bunch and select. Manufacturing, just doesn't allow selection of gain and neither does distribution. Gain DOES have a variation with the operating point, so if you use a simple circuit to measure the gain, you will still need a reference.

It's not important what the gain is, just that all of the transistors used in parallel should have nearly the same gain.

Looks like they are around a USD $1.00. From Mouser, digikey and Allied, they are about $2.00 each. Jameco has if for about a buck as well, but they also have a A version. Wider gain range for one.

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#40

Re: Little Help With Repair and Guidance

02/10/2013 3:07 PM

The resistors I see (brn, blk, red, silver) is 1K and not indicative of current sharing resistors. They may be elsewhere: they are USUALLY attached to each emitter of each transistor in parallel. Some look like a white sandstone box and others like a gold heat sink with two leads.

ONLY if the transistors are connected in parallel with an emitter resistor on each can you remove one of the transistors. For a 40 A supply, I would think you might have around 6-8 2n3055 transistors in parallel.

The emitter resistors would probably be less than 0.5 ohms. They are usually fusable, wirewound or could me metal oxide in modern times. Metal oxide likes to disintegrate when overloaded.

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#41
In reply to #40

Re: Little Help With Repair and Guidance

02/10/2013 3:39 PM

KISS - Looking at the last 2N3055 that is supposedly "bad" and marked as "40", it is connected to the other thermostatic switch, via the base which is also seems to be connected to the collector via mtg. screw!

It seems to me that it is being used as some sort of a "Zener or reference diode" since base is shorted to collector configuration then to the bi-metalic thermostat. I got a feeling this may be configured as a reference for a "crowbar' protection ckt? The small green wire coming from the thermostat goes to where?? something to be explored...

Good luck!

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#43
In reply to #41

Re: Little Help With Repair and Guidance

02/10/2013 6:24 PM

The Green wire goes back to the circuit board.

The two small resistors 82 oms are reading 1.014 Out and in the other one reads 1,028. these do not pass a sound continuity test. All other resistors do pass the sound test with two of my multimeters.

grey, red, Black.

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#45
In reply to #40

Re: Little Help With Repair and Guidance

02/10/2013 8:25 PM

humm

Yes I am on the crash course so I am wondering why you look at the color codes backwards?

Brn Blk Gold Sil. should be 10,000

and brn blk red sil should be 1000

Ok now I get it the direction is looked at by the direction of the "tolerances band" being the last thing to read. Is that correct?

Only one question left here. I only have one 1000 resistor out and one in place. they both read basically the same values. No problem...

My question is why the 10,000 ohm resistors "still in place" read no where close to what they should. They all measure 1.9 ohms? am I way of with my thinking, or am I reading the color codes backwards again?

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#48
In reply to #45

Re: Little Help With Repair and Guidance

02/10/2013 9:30 PM

The proper way of measuring the resistance (to verify its value) is to disconnect one of its end before doing any measurements. Otherwise you may end up measuring other (component) resistances that are in parallel to that resistor, thereby giving you false readings!

Also, if the resistance readings you are getting is changing and not steady the longer you leave the probe on that junction, you are actually charging a capacitive component that is connected with that component!

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#49
In reply to #45

Re: Little Help With Repair and Guidance

02/11/2013 12:01 PM

10,000 ohms would be brown, black orange.

what you have should be a one ohm resistor. With your meter lead resistances added in you probably have a good measurement.

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#42

Re: Little Help With Repair and Guidance

02/10/2013 3:51 PM

Good point. Looking closly, it almost looks like the B and/or E is shorted to the heatsink. Those pins seem too close.

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#46

Re: Little Help With Repair and Guidance

02/10/2013 8:26 PM

Well, it does look like the 82 ohm resistors are bad.

Are any of the pins of the transistors really close to the heat sink?

It's extremely difficult to get a OHM reading on a transistor, BUT a short is a short. If your meter has a scale with a diode symbol on it, that's the scale you should use to test the transistor junctions in both directions. The B-E will be the most prominent diode.

Watch the use of m. m-ohm is milliohms and M-ohms is Meg ohms. I suspect your earlier measurements were in the Meg ohm range?

Carbon resistors typically change value and get larger when they fail.

The posts seem to be a little mixed up - moderation?

That still doesn't explain the 0V reading on the B-E pins UNLESS the pins were shorted to the heatsink.

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#50
In reply to #46

Re: Little Help With Repair and Guidance

02/11/2013 6:16 PM

FYI I found I was reading my stripes backwards and the at 82 ohm turned out to be the 1K ohm instead. ( buy measurement)

All pins are dead center in the holes on the heat sink.

I revamped a couple of 1.5 v "C" batteries and put together a continuity tester with a headlight from an old modern car.

One of the pins are shorted to ground where it bolts to the heat sink.

And there is a direct short across B-c pins.

( Note ) There was no heat sink compound under it nor anywhere I can find.

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#47

Re: Little Help With Repair and Guidance

02/10/2013 8:48 PM

Don't forget to take an AC reading from the scope case to the power supply case. No need to connect a probe, but make sure you have the same conditions that you had before.

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#52

Re: Little Help With Repair and Guidance

02/11/2013 7:50 PM

Quote

One of the pins are shorted to ground where it bolts to the heat sink.

And there is a direct short across B-c pins.

( Note ) There was no heat sink compound under it nor anywhere I can find.

End Quote

I don't understand the first two sentences. The lack of heat sink compound is a slight problem.

So, there is a B-C short when the transistor is not connected to anything?

I thougt we sort of decided that the heatsink is at a non-ground potential. Thus short to ground at the heatsink i don't understand what it means.

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#57
In reply to #52

Re: Little Help With Repair and Guidance

02/12/2013 11:40 AM

OMG the # 40 transistor is out of the case. Nothing to ground too or ground out to.

When I run a continuity test to itself; Itself meaning the place where it bolts to the heat sink on the transistor itself! One of the pins prove a direct short and will light the bulb. the other pin does not show proof of a short when directly contacted to the base of the transistor.

Lastly the B-C pins in series show a direct short between them lighting the bulb.

I will investigate why the potential is showing up at the heat sinks.

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#59
In reply to #57

Re: Little Help With Repair and Guidance

02/12/2013 3:59 PM

Just a word of caution and a reminder:

Using a home crudely made continuity tester like, a (bulb in series with some batteries), may work to verify continuity. But this same testing methodology may also create or cause a self induce problem when use in testing whether a transistor or a P-N junction is good or bad! Doing a static junction tests is a matter of creating a forward or reverse bias condition on the P-N junction done with the injection of predetermined and limited amount of DC current.

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#60
In reply to #59

Re: Little Help With Repair and Guidance

02/16/2013 3:51 PM

Thanks for the input. i have been working doubles and no time to return here. I thank you for the input. i had found a similar batch of minutia stuck in my brain and took myself back to (how little I really know), about this stuff. I did realized this is an NPN or a PNP transistor and I really don't have any experience testing these devices at all!

However I do have plenty of meters that should do the job. I will start testing tomorrow.

I will look into absolutely everything I can to get myself educated enough to fix this device.

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#54

Re: Little Help With Repair and Guidance

02/11/2013 8:13 PM

With the 4-band code: http://www.michaels-electronics-lessons.com/resistor-color-code.html

The brn blk gold silver should be 0.1 ohm 10 % resistor. Gold has a multiplier of 0.01

10 * 0.01 = 0.1

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#58
In reply to #54

Re: Little Help With Repair and Guidance

02/12/2013 3:04 PM

I need a breather. gasping for air. I'm so glad I am here asking questions not the other way arround.

I have been so off base with some posts. sorry

the pins on the transistors Bace and Emmiter ok,

then the one tenth ohm resistor "nice" 10*.01 thanks so much .

I'm learning

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