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Volume Control Knob on Clock Radio is Faulty

07/08/2012 3:55 PM

I've got a small Toshiba clock radio. When I turn the volume knob, there is no smooth transition of volume. Instead, there is a lot of static until I hit a certain point, then the reception is clear again. Somewhat random. If I leave the volume at certain settings, there is no reception. It's very touchy. It seems like it might be a cleaning/build-up issue in the rheostat? If so, what part should I clean, and how? Or is it something else? Not a terribly expensive radio, so would just buy a new one if it involved buying parts.

I would understand this type of thing with the tuning knob, but not quite sure what's going on with the volume, that would give me static, or even silence.

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#1

Re: Volume Control Knob on Clock Radio is Faulty

07/08/2012 4:07 PM

You could try some contact cleaner, WD40 or similar (possibly compressed air) on the potentiometer as sometimes they develop high contact resistance (which can cause the problems you are mentioning - scratchy response, no signal, etc as the signal going to the radio's volume opamp fluctuates).

Obviously you will want to do this with the power off and leave the radio to air out a bit. Alternatively you could replace the potentiometer (which shouldn't be too hard to find). I don't think it is a dry joint on the circuit board but it may pay to check also.

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#3
In reply to #1

Re: Volume Control Knob on Clock Radio is Faulty

07/08/2012 7:58 PM

Years ago, on a boom box, I had the same issue. I tried contact cleaner, but it destroyed the pot. I believe the pot was made with a resistive surface backed with a plastic support. The contact cleaner melted that plastic support and afterwards the wiper would no longer make contact at all.

I was able to contact Toshiba and get a replacement pot. That was nearly 20 years ago. I'm not sure how they are with repair parts now.

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#5
In reply to #3

Re: Volume Control Knob on Clock Radio is Faulty

07/08/2012 8:39 PM

The materials haven't changed too much for the plastic potentiometers, it just sounds like you used a WAY to aggressive cleaner.

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#22
In reply to #5

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 7:59 PM

That's what got me, the contact cleaner was from Radio Shack! I didn't expect it to destroy the pot. At the time, I chalked it up to Toshiba using the cheapest pots available.

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#2

Re: Volume Control Knob on Clock Radio is Faulty

07/08/2012 5:39 PM

Sometimes you can get away with a very small repositioning (gentle nudge) of the contact that slides along the resistive film inside the potentiometer/volume control. Sounds like the resistive film has worn and by shifting the contact onto a clean track most pots work again.
...that's assuming the pot isn't encased in a bulet-proof housing

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#7
In reply to #2

Re: Volume Control Knob on Clock Radio is Faulty

07/08/2012 9:21 PM

Thanx Oz... that would have been the next thing I tried.

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#4

Re: Volume Control Knob on Clock Radio is Faulty

07/08/2012 8:35 PM

You've got corrosion.

Sometime, when you have nothing else to do, turn the knob from min. to max. about 100 times, Smack the radio on its front, then bottom, a few times in between and then try it.

If that doesn't cure it, place it on a concrete block at least 6 inches thick and beat the hell our of it with a big hammer.

Buy a new radio.

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#8
In reply to #4

Re: Volume Control Knob on Clock Radio is Faulty

07/08/2012 11:36 PM

Lyn's on the money, except at the end -

Do it w/o contact cleaner first (100 turns up and down) Then try it.

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#6

Re: Volume Control Knob on Clock Radio is Faulty

07/08/2012 9:19 PM

I appreciate everyone's excellent and timely solutions, but I ended up figuring it out by myself, without even taking it apart. What I did was, I turned the knob from min. to max about a 100 times, and then I smacked it on the front and bottom. I think it just had corrosion and I knocked it loose. Now it works perfectly! I should have thought of that earlier!

But thanx again, everybody!

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#16
In reply to #6

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 3:38 AM

So, beating the hell out of it with a hammer didn't work?

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#17
In reply to #16

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 3:55 AM

It will, next time.

Feels good, too!

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#9

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 12:07 AM

The stuff you want to clean electrical contacts and potentiometers and rheostats is called "DEOXIT." I question the wisdom of using general purpose solvent.

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#18
In reply to #9

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 3:58 AM

You should also question the wisdom of using a hammer.

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#10

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 12:07 AM

WD40 is a poor choice for a contact cleaner. It will leave a residue that will attract and hold more foreign material, thus exacerbqting the problem. Look at your automotive store for products such as brakleen, CRC brake cleaner or theirequivalent. These spay products contain purer solvents that leave no trace of residue. The highly pressurized cans will blow your rheostats back to their duty.

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#12
In reply to #10

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 12:45 AM

...or CRC contact cleaner. No need to improvise if you have to buy it anyway.

WD40, as you say, will leave an oily residue and become a crap magnet on a pot. It is, however, just the thing for terminals especially if they get wet or have to work in aggressive atmospheres.

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#11

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 12:18 AM

I have had the same thing happen on several occasions & as "jack of all trades" said spray some WD40 into the volume pot & turn back & forward it will fix the problem I have done this several times with good results so jack gets a GA from me

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#15
In reply to #11

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 3:35 AM

I only used contact cleaner once because it dissolved plastic the first time I tried it & the radio I was fixing was worth less than the price of buying a can of the contact cleaner that would be suitable, so WD40 was the economical solution considering I already had a can of it

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#13

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 2:57 AM

Chuck it, It amazes me that radios in the 50s-60s were beautiful, the sounds were perfect the tones were were perfect all this was MW, then we got HF that moved on & off station at will, now VHF which means one can get crisp clear sound, as long as nobody moves and you're not in a vehicle, thats progress.

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#14
In reply to #13

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 3:24 AM

AM MW still proliferates.

The FM VHF receiver in my car works just fine and doesn't display what you've described.

HF is still beamed around the place too.

You can choose what you listen to you know..

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#21
In reply to #13

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 11:50 AM

I have and use an old Marantz 2230 amp. It was rebuilt by a tech and he just used regular contact cleaner. The sound is unlike all these present day supposed 1000 watt amps that provide 1000 watts for maybe one second.

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#19

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 6:31 AM

The pot is worn out, but you can probably measure it end to end for the resistance if its not marked. You also need to identify if its log or lin, usually log.....

Measure it physically and buy the best quality in that size and style....

PS. To measure if log or lin use an ohmmeter and using the "good" part of the track, measure the resistance between one end and the wiper.

Note the value. This your "0" value, take this off all subsequent measurements.

Move the pot say 20°, measure again.

Note the new value, minus the first value.

Move the pot again about 20° (same distance as before)

Note the new value, minus the first value.

On a linear pot you will measure about the same value each time, other than the first of course!

On a logarithmic pot you will either measure double or half the value.....deoending upon the direction you turn it....

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#20
In reply to #19

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 6:48 AM

...or move the pot to the mechanical 50% point and measure the resistance in each direction ie wiper tag-cw tag and wiper tag-ccw tag. If they are the same it is linear if not then its log.

Otherwise look for the A marking which means log.

OP's already sorted this with a good old wrist hone and rattle.

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#26
In reply to #20

Re: Volume Control Knob on Clock Radio is Faulty

07/10/2012 4:50 AM

As you know forgotten from reading the OP's posts, only certain parts of the pot are usable.....which is why I recomended the other method of obtaining as to whether its a lin or a log version.......

Your method works well for a pot in a known reasonable condition only.....anything else and it may not even read anything at all between wiper and either end...

Probably a good practical method would be to use your method first and make sure its right (assuming you get a reading at all) with my method......agreed?

BELT AND BRACES?

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#27
In reply to #26

Re: Volume Control Knob on Clock Radio is Faulty

07/10/2012 5:17 AM

Agreed.

Even "your" method is dependent on a reasonable portion of the resistor track to be continuous.

If it's that buggered then any testing is academic and a log pot replacement would be the right call. Volume pots are log.

Anywho... OP's declared this problem fixed.

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#23

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 9:20 PM

CRC's Brakleen and Electromotive contain the same ingredient. Brakleen costs abut half. I think it's toluene.

I melted a DVD by using too strong a cleaner on it. Now I use Pledge spray on furniture polish. If that doesn't work I take it back.

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#24
In reply to #23

Re: Volume Control Knob on Clock Radio is Faulty

07/09/2012 10:43 PM

My can of CRC contact cleaner doesn't have the active ingredient on it.

It does say "plastic safe formula" in a friendly font.

Toluene and plastics don't mix well. I guess that the contact cleaner and brake cleaner aren't the same deal.

Regarding cheaper alternatives CRC contact cleaner is similar in price to WD40 here so I'm a little spoilt and don't have to resort to alternatives. There are other things that are the other way around here too so it's swings and roundabouts.

BTW I use toothpaste on my CDs and follow up with Brasso. Same same for helmet visor. Gets it nicely rejuvinated.

Pledge costs more than CRC contact cleaner here just to give you all an idea of comparative pricing.

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#25

Re: Volume Control Knob on Clock Radio is Faulty

07/10/2012 3:36 AM

Just squirt some switch cleaner into the "can" behind the knob and spin it up and down a few times. Also check with a volt meeter to make sure there is no DC voltage present. If there is you may need to replace a cheep capacitor.

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