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Author Topic: How to determine what's what on a pot?  (Read 2483 times)

Amp

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How to determine what's what on a pot?
« on: September 26, 2013, 09:57:13 PM »
I figured you lads would be able to answer this question if anyone could.

So, I have one of these electronic Tanburas, like this.



One of the pots seems to be bad and wouldn't clean, so it needs replacing. Upon disassembling and  doing basic diagnosis, the inside was a total Yugo. The plastic bodied pots they used were utter trash and several came apart, there were any number of half-assed jobs, etc.
OK, it needs a complete repot. There are 6.

The pots themselves are rather odd and I seem to have found what looks to be a brilliant alternative in a metal, similarly sized 100K pot NOS Russian pot with the right shaft diameter and pot size to fit in the chassis.



My original plan was to just replace the pots by desoldering and resoldering onto the same tab, since the existing pots are just like the conventional ones with the three side by side tabs.



Question: How do I determine what wire goes where, desoldering from a Side by Side by Side pot onto a pot as seen above, where the tabs are arranged on the bottom like that?



« Last Edit: September 26, 2013, 09:59:33 PM by Amp »

Roly

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Re: How to determine what's what on a pot?
« Reply #1 on: September 27, 2013, 10:03:44 AM »
Well I'll have to admit I had to Google Tanbura/Tanpura and find a demo on YouTube.

In answer to your question, see appended drawing.

HTH

If you say theory and practice don't agree you haven't applied enough theory.

Kaz Kylheku

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Re: How to determine what's what on a pot?
« Reply #2 on: September 27, 2013, 09:25:51 PM »
Question: How do I determine what wire goes where, desoldering from a Side by Side by Side pot onto a pot as seen above, where the tabs are arranged on the bottom like that?

So you have a pot with three terminals, and you don't know which two are for the main resistive element (and in what orientation) and which are for the wiper?

Assuming the pot is functioning, what you can do is:
  • turn the pot all the way left or right and measure all three possible resistances
  • one of the resistances will be nearly zero, and that means one of the two lugs that have close to zero ohms between them  (let's call these two T1 and T2) is the wiper, and the other one is of course the terminal which contacts the wiper when the pot is turned to that position
  • now turn the pot completely to the opposite side and check the resistance from T1 to the remaining terminal T3, and from T2 to T3. If T1 is now zero to T3, then T1 is the wiper. Otherwise T2 must be zero to T3 and it is the wiper.

Then, for future reference, take a fine felt tip pen and write these letters somewhere on the pot: L, W, R: L close to the terminal that shorts to the wiper when the pot is all the way left, W close to the wiper terminal, and R close to the terminal that shorts to the wiper when the pot is all the way right.
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Amp

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Re: How to determine what's what on a pot?
« Reply #3 on: September 29, 2013, 07:53:01 AM »
Thanks much guys.
The NOS pots are actually incoming from Lithuania, so I'll report more when I get them in hand.

I am a beginner at this, I know just enough to open stuff up and get myself into trouble once things get beyond cleaning contacts  :duh so I will certainly have some more questions (and will furnish detailed pictures of everything involved) as soon as the pots arrive.

It's quite likely this may actually need some additional troubleshooting which should be quite a thrill ride since there is ZERO English language technical information about them... Unfortunately, punting this and buying new is not an option. This particular model with pot adjustment for all the tones is, to the best of my understanding, now out of production. In my opinion, these are vastly superior to the new designs so it must be kept alive at all costs.
« Last Edit: September 29, 2013, 07:59:05 AM by Amp »