Defective Electronic Boards Causes Supply Fuses To Blow?

No way to know for sure, it depends on what the "board" is. Many VFDs now lump what used to be discrete components onto boards for mass production. So you now may have a "board" that comprises the line surge protection devices. If that's the blown board, it's entirely possible or even probable that it would clear fuses ahead of it. You can usually no longer replace any one component either, you can only replace the entire board.

It could also be a firing board and if it failed, it cause cascading problems with ALL of the power components. Don't be surprised if you find out after replacing it that there is another failure either immediately evident, or taking place shortly thereafter.

Lightning is a harsh mistress.

The problem Jraef is that the technician tested the board to other unit, and as he said supply fuse again is busted.

Does his story really true. My assumptions(correct me if Im wrong) if the board had been destroyed by surge, this will make the whole circuitry open and therefore does not cause any short voltage to supply that will cause blown fuse, how come that when the board circuit is defective--> fuses blow.

I don't get, it. The most probable scenario I can think of, is they have wrong wiring termination. Well, the board is just about 5,000 USD and I want to correct it as early, cant afford to lose another board. I'd really appreciate some one could enlighten me here.

You are falsely assuming it is going to fail "open". It's maybe more likely something failed either as a direct short circuit or a trigger condition that causes a short circuit. If you fire power components in the wrong sequence, you can have that happen. Again, no way to determine anything useful without knowing the exact nature of the "board".

JRaef is right. Most likely a short. Usually, resistors open, capacitors sometimes short, but my money is a transformer. At $5k I'd add a surge protector to the new one.

What are you wanting? Do you want us to condemn your technician? He has told you it's faulty, if you don't believe him send the unit for independent testing.

We can't 2^nd guess what's happened.

Yap, that's why I am asking here TOnyS because I don't like guesses.

Send the unit for independent testing then

If no experts around here CR4 might as well send it. I'd really wish anyone here in CR4 knew some thing more about this.

Electronics troubleshooting if done online is hard and ineffective, since it just become a guessing game for everybody? There are several approaches or techniques in troubleshooting, and you happened to choose the easiest and probably the more costly way, and that was troubleshooting by substitution!

Time wise, Troubleshooting by substitution may work if problem is isolated or localized in only one board? If not, it will be more costlier since you may end up replacing every ckt boards in the system before finding the real culprit..

Also, if the defective ckt. board is the multi-layered type, replacement maybe your only option, unless of course you /your technician is an electronic expert. Knowledgeable and equipt to do a more complex and effective troubleshooting?

Blowing fuses are normally caused by shorted or leaky component(s) as already emphasized, stated earlier by experts here in CR4. For an effective and successful approach to resolve this and future problem(s), the troubleshooter need a more in depth knowledge of electronic devices, there characteristics and how they will behave in any given circuit.

Yap, true, but i'd like to learn.

So you want a circuit designers opinion on an a circuit/board that is undefined? Is that right?

Yap, as this applies generally to circuits. It is because, I can not in my own knowledge for circuits when its defective, it blows off the fuse. Either the circuit is designed to blow fuse when some part of the board is defective or my technician is lying to evade liability from wrong termination.

I can not accept the idea that it will blows the fuse not unless somebody has to explain me here. What causes the fuse to blow in the first place.

Say for a simple circuit compose of a power supply(transformer, rectifier, filter) --> amplifier --- IC for (adjustments) say being hit by surge..

Would you expect to blow the fuse at the power supply side?

Perhaps at first when the surge was there, probably as you replace the fuse and run the circuit again, most unlikely, the fuse wont blow again right?

If it did blow in the second time around that means, the circuit is short.

The next question is, what make this circuit short, is there a circuit element(resistors, capacitors, transistors, diode etc) that will make the circuit short when defective?

You got me now?

why not fill in a few more details

model #

part # on the board in question

wrong termination will not generally cause such a problem...

I think he meant the technician is lying to avoid wrongful termination of employment. The OP is expecting the impossible. He wants the designer of the board to step forward and fix the problem without even giving the manufacturer or model number! He has received good advice and has blown it off.

It seems, you have little or nonexistent experience repairing boards, based on your statements.

Mother nature can and will do anything she choses, via lightning.

It seems, your technician is sitting there with inadequate docmentation a DVM, and a soldering iron. Trying to make sense of a complex digitally controlled power unit., that refuses to work. Factories and repair stations use complex setups for every single step.

Wit a decent setup there, by now we would be discussing chips and components, and there is no trace of that, yet.

And you want to do it barefoot. Good luck!

> I can not accept the idea that it will blows the fuse not unless somebody has

> to explain me here. What causes the fuse to blow in the first place.

Only better supervisors would ask such damning questions. If the board is blowing a fuse, any good tech can easily identify the part that is shorted. It is that obvious, easy, and done quickly. Techs who only know because the board causes failures will then quickly assume it was destroyed by a surge. Surges are popular myths cited mostly because the myth is popular. Often because many who blame surges do not learn how surges do damage.

Drive boards are often easily diagnosed when a most common failure is shorted drive transistors. These are be quickly located with a minute, an ohm meter, and some basic transistor knowledge. A fact that should be learned so that other overstressed parts are identified before they too cause failures. We rarely fix things to save money. A number one reason for fixing things is to learn from the failure. To avert future failures both in that unit and it all other units.

Once a defective semiconductor is identified, then both the incoming and outgoing surge path is identified. A surge did not enter on one wire, cause damage, and then stop. One must forget elementary school science to assume that. What must exist: a complete path incoming on one wire into the building, incoming through that board, outgoing via some other board conductor, and then via some building conductor to earth. That lists all currently or potentially future damaged parts. And identifies how all future failures are averted.

A part deep inside the board is not damaged by a surge. Most parts fail due to manufacturing defects. If no incoming and outgoing path is identified, then no surge entered and exited that board. Manufacturing defects can occur even years later.

Let's return to those drive transistors. One connects a plus voltage to a motor. The other connects the minus voltage to that motor. If either transistors conducts constantly (is shorted), then plus voltage is shorted directly to a minus voltage. A fuse blows to avert a fire due to a gross and obvious failure. That any good tech can identify..

Parts that blow fuses are some of the fastest and easiest to identify. The defective part is identified so that future failures can be averted. Anyone who cannot say what has failed and why should result in those (your) damning questions.

Well, i dont mind being a "damn" learning rather than doing nothing.

I honeslty accept I am new to PCB trouble shooting and forgive me I'm not into electrical engineering. It just so happen it crossed my areas of responsibility that I myself had to investigate such.

And I will not tolerate a "lousy and lier technician" under my branch.

I assume people who got experience in troubleshooting with board would experience this common problem.

But well, could they explain the cause, other than believing and making it a traditional myth.

NOTHING DOING without detailed Circuit Diagramms and proper instrumentation. This is not the 1940's anymore.

Assuming, that the tech is lying is unhealthy and counterproductive. What is likelier, that the tech is underequipped in equipment or training. Ranting does not help in either case.

Tell us what you have, then maybe this running in circles stops.

For an effective approach to resolve this and other future problem(s), the troubleshooter need a more in depth knowledge of electronic devices, characteristics and can predict how they will behave in any given circuit. One also need to utilize their senses as in smell, observation, listening and possibly feeling, - but not much on the talk while troubleshooting.

A good starting point is to identify some major part numbers used in the driver board. Depending on its vintage, power drivers may either be SCRs or IGBTs, and some other nearby components that triggers the drivers.

> And I will not tolerate a "lousy and lier technician" under my branch.

Nobody said anything about lousy or lying techs. Damning questions are asked to identify a problem. As leveles noted, "the tech is underequipped in equipment or training." Providing that attitude and knowledge is a supervisor's job. A task that cannot be implemented without understanding how the work gets done.

I respect their 15 years of experience but it wont be good enough to make things rightfully done. That's why I ask here. Assessing everything they say in comparison to "experts opinion". There are only 2 assumptions i have about on the problem.

Either;

1) Circuit designer intend to put a somewhat a relay contact to short fuses to protect other controller board when one is defective

or

2) A circuit element had cause the short and what is that element in the first place?

I assume expert's in the field could answer that.

Noudge,

As an electronics tech for 25+ years, and a PCB Designer for 5+, I can tell you that your "assuming" is WAY off! There is no way any "expert in the field" can tell you what is causing the failure without any DETAILS of the equipment in question! If troubleshooting electronic equipment failures was so easy, there would be no reason to retain the services of technical staff. If you continue to treat your techs like it seems you are, you may end up in that situation.

Follow the techs advice until given a good reason not to, no one on an online forum is going to be able to second-guess an on-site diagnosis by technical staff, without a LOT more details than you have been willing to provide. Period.

Tom D.

Some people obviously have never worked as a service tech in the real world. Having done tv service for a number of years I can tell you lightning and surges can and do cause multiple failures, some may be low level components driving power devices that could check good in static tests but cause high current draw dynamically. Why do you expect anyone to troubleshoot your board from a distance with NO information. If I was the tech I wold quit!

Nope, they are given diagrams for controller board termination.

Noudge79 posted:
> There are only 2 assumptions i have about on the problem.

A benchmark to identify better techs is found in reasons 'why he knows'. That means numbers and basic technical concepts. For example, if a surge caused damage, then he can identify the incoming and outgoing path of that surge current. So that future surges never cause failure. Surges are routinely averted when proper protection is installed. That means no protector adjacent to the controller. Superior designs inside a controller do more than any 'power strip' solution can do. Surge damage is identified because surges must never cause damage.

A more common failure is the manufacturing defect. Another problem often averted by identifying the reason for that failure. In this case, identifying a failure common in too many controllers. Only better techs avert future failures because the reason for that failure is identified.

Everyone has heard the expression, "Follow the evidence" from CSI. Far fewer understand what that really means. For example, anyone who 'followed the evidence' also saw through the 'Saddam WMD' myth. Numbers exposed that myth. Same applies to electronics repair. To follow the evidence, one does not say, "I saw this happen; therefore fixed it by doing that." Instead, one collects symptoms without changing anything. Then lists the 'usual suspects' for those symptoms by using basic electronic concepts. From knowing what could cause each symptom. And then eliminates each suspect by viewing hard facts using well proven diagnostic methods. Swapping parts on speculation is rarely good procedure. That 'shotgunning' is how even automobile mechanics become quickly unemployed.

For example, defective power supplies can cause strange controller failures months later. But numbers combined with underlying concepts mean a defective supply can be identified before failures happen. Conclusion obtained by not even disconnecting one wire. At the management level, asks whether he is using numbers or diagnostics to first identify a problem. Conclusions without hard facts and numbers define junk science.

Some rather entertaining and enlightening examples of how this is done are found in "Tales from the Cube" in [url=http://www.edn.com/channel/Tales_From_The_Cube.php]Electronic Design News[/url]

An example of how a tech can be driven from thinking logically: A computer would crash repeatedly during the day. All night long, a tech would execute diagnostics that would not fail until he left the room. In frustration, that tech would loudly announce that he was leaving the room for coffee. Stomp out. Then sneak back to peer around the door. That computer still would not crash until he actually did go for coffee.

Only a better tech would stand back, follow the evidence, and eventually identify an actual suspect. Eventually, a hard problem was found. A computer only crashed when he used one elevator. That computer was improperly grounded to the elevator. By following evidence, the actual problem was identified. Another example of why those with lesser experience would resort to shotgunning. Even install power conditioners when a controller's supply already does better conditioning.

Shotgunning means not finding the actual problem. A problem often seen by a consumer magazine that created minor problems in computers. Then got plenty of perfectly good parts replaced by too many computer techs.

A most common symptom of a tech who is only shotgunning: he blames it on a surge. Does not identifying and eliminate where that surge path was both incoming and outgoing. Did not identify or eliminate an unnecessary reason for that damage.

If you had a large enough "surge" such as lightening, insulation barriers could certainly be broken down, elements and wires can be fused etc., which could cause a short.

What is the rating of the fuses that blow?

Do they blow immediately on power-up or when the drive is started?

This may simply be a case where the technician is correct, and the supervisor is not.

"The technician were given a diagram of interconnects". For troubleshooting internals. Yeah, right. And no answer for any of the details. This guy deserves what is coming to him.

It's actually a (GECB) Global Elevator Control Board.

If what you are after is a deep understanding of exactly what happened and why the fuses continue to blow, that will require what is often called a "Root Cause Failure Analysis" or RCFA. It is a very very intense deconsrtuction of the PCB and EVERY component on it to see what failed, along with a deep understanding of the overall purose and function of the PCB in order to determine what failed first, how that caused the next failure etc. Sub assembly components need to be sent to the original mfrs for their own RCFA as well. A typical RCFA on a VFD board takes 3-4 weeks (AFTER working its way in the cue to be started on, whjich is sometimes a few weeks as well). There is just too much that goes into it to be done rapidly with any kind of reasonable accuracy, yet anything short of that is a waste of time because there are so many possibilities. It's virtually impossible to do this in the field.

At my company we require a minimum fee of US$750 be paid up front for an RCFA, even if the cause is suspected of being a warranty failure. This is because the process is so intense and expensive that even this amount does not cover it and if it were strictly an economic issue it is ALWAYS less expensive for us to just replace the board. So the only reason to do an RCFA is to either a) ensure that whatever the cause was, it can be addressed so as to avoid being repeated, or b) assign blame because of an extreme economic loss as a result of the failure. It's not something to be undertaken lightly in any case and I think you should re-examine your position on impinging the veracity of your technician. If he knew there was a lightning hit and the board is now causing fuses to blow, it needs to be replaced. Spending a bunch of time to see EXACTLY why is counter productive in most cases.

Well, thanks for the info man. it's actually quite worthwhile having conversation with all of you while learning. I already ordered a replacement board, I just hope the new board will work, no more fuses to blow, otherwise the technician be better be liable for what he is doing.