Help Required - Slide Potentiometer

[Rich J]

Hi All - this is my 1st visit to the forum so I hope this is the correct place to post my query and I'm not an electronics savvy person as you will see from the following!

I have a broken volume control (slide potentiometer) from a Technics PX30 digital piano - sadly long since out of production.

The pot has little info on it other than ALPS - JAPAN (stamped on the ends) and along one edge are printed the numbers 6W-5KBx2. (The first 2 digits are rather faint - may be 8W) My local electronics shop advises it is a 5000 Ohm dual (stereo) channel pot which they are unable to source. Ditto Maplin.

I found ALPS online and spoke to their people (unfortunately not a technician) and they could do nothing without a part number. Ditto Mouser and several others (Maplin, CPC-Farnell etc etc). Sadly, I don't have a wiring diagram for the piano - I've put out feelers to various digital musical instrument forums but nothing yet has come to light over several weeks - so no part number. I've tracked down a pot in Germany that is identical in every respect (bar one) that would fit my board but it is the 'bar one' that I need advice on.

The German pot is rated as 10K Ohm and my question is - would fitting this have a detrimental affect on the other components on the board in electrical terms? My assumption is that a 10K pot would offer twice the resistance than a 5K pot, but does this relate to half the voltage/current being passed through? (If so, and say the volume would only be 50%, then I could live with that). Also, is the resistance rating (as in the numbers above) per channel thus equalling 10? Or have I got that completely wrong? Naturally, I don't want to fit an incorrect part and blow the rest of the board!

I have other info I can post (sketch, with sizes of the pot and link to the German site) if you think these necessary.

In all other respects, the piano is in excellent condition and played beautifully until the volume control packed up! It would be a shame to scrap a good instrument for the lack of, what is, a relatively cheap component.

Any light that you can shed on this would be most helpful!

Thanks in advance for your time.

Rich

[David]

It is difficult to guarantee that using 10k pots rather than 5k ones will have no ill effects. However, it is usual for volume control pots to be very tolerant of the actual values in most cases. (Is the designer having a 5k, 10k or 25k day? That was actually said to me many years ago!) As you have the good chance of getting a usable piano at the end of things I would suggest that you just try the 10 k job.

The indicated resistance value will be per section. Incidentally, do you have a meter which will enable you to measure the value of the resistance of the old pot - when it is removed from the board, of course. If you have a spare 10k pot , say of the more usual round type, you could always wire it temporarily in place of one of the sections of the broken two gang one and see if that works on one channel is OK before you order the new two gang one.

[magpie]

You might have to leave the slider control out of your thinking for replacement, as it could be difficult to get the exact size physically and electrically.However,you could fit an alternative volume control potentiometer,( like you have on a car radio ) fitted somewhere on the consul for convenient access.With that in mind, I have looked on the RS Components web site, and have come up with one that should do the job.Have a look yourself,to see what I am on about.The reference is 484-9247.

[Pauldf]

Also pay attention to wether it is linear or logrithmic, (lin or log), volume controls are usually log.

[Rich J]

Hi Guys - thanks for the swift replies!

@ David
I don't have a meter myself but I know a man who does! However, with the pot being u/s, would it show a reading across the relative pins, end to end?
Also, how do you calculate the difference from one pot to another? I assume that mains voltage would be transferred down to say, 12v, for the board to take it? I need to know the relative difference between 5kOhm and 10KOhm and the effect it would have on output. If the difference in voltage/amperage is huge, then other components/speakers etc may 'blow' rendering the whole board u/s.

@ magpie - Thanks for the reference.
It may well come to that in the end but for the time being I'll carry on the search. And it is beyond my skill level and knowledge to make a radical change like that. If I can source a direct replacement (or an alternative) then the job is relatively straightforward. I have already removed the slider from the board cleanly so am confident in re-fitting a new one.
My reasoning is that there were relatively few pianos produced overall in this range so, logically, the electronics would be made up from 'stock' parts rather than bespoke. Technics produced several similar models at that time and my guess is that most of the control boards would have been interchangeable, otherwise production costs would have been massive? If I can find a wiring diagram for this one, then the chances of someone, somewhere stocking the correct part gets better!

@ Pauldf - Which one? Mine or the one magpie refers to? I'm advised mine is linear. Apologies - I should have made that clear in my original post!

Thanks to all for your time on this.

Rich

[David]

I hope you don't mind this suggestion, but there are several very good books about electronics and design mentioned on this site. My personal favourite is "The Art of Electronics" by Horowitz and Hill - perhaps a bit pricey, but imo worth every penny ...

[Pauldf]

Just in general, volume control in amplifiers for sound is usually log. He'll just need to double check as a linear slider fitted where a log one ought to be won't work very well.

[Rich J]

I hope you don't mind this suggestion, but there are several very good books about electronics and design mentioned on this site. My personal favourite is "The Art of Electronics" by Horowitz and Hill - perhaps a bit pricey, but imo worth every penny ...

All suggestions welcome! However, this is very much a 'one-off' so making such an investment would, alas, be a waste. But thank you anyway!

Rich

[Sock Puppet]

Hi.

Have you contacted Technics about a replacement? Or asked your question on a Technics forum where you might get a manual too?
As it is, if the physical dimensions are fine then a 10k pot would be fine in the volume control position. The "B" in the description means linear though I'd have thought a logarithmic one for volume. Either will "work" they'll just be very different.

Cheers,

http://technicskeyboards.com/

[Rich J]

Hi.

Have you contacted Technics about a replacement? Or asked your question on a Technics forum where you might get a manual too?
As it is, if the physical dimensions are fine then a 10k pot would be fine in the volume control position. The "B" in the description means linear though I'd have thought a logarithmic one for volume. Either will "work" they'll just be very different.

Cheers,

http://technicskeyboards.com/

Yes, I'd posted on that site before I found my way here. Unfortunately no response for a picture of a wiring diagram was forthcoming.

However................. UPDATE

I used an online calculator to see the difference between a 5KOhm and 10KOhm pot. (My main concern was to not increase the voltage/current across the PCB in case I 'blew' the circuitry). A 10KOhm pot put through half the amperage than a 5K, as it turned out, so I took a punt that the pot from Germany would do the job. It duly arrived, was fitted and the instrument plays once more! (My assumption that it was the pot at fault proved to be correct). All for less than £10.00 delivered!

Time will tell if there are any ill-effects but so far all seems ok. Again, (an assumption), if there were to be any issues they would have happened at 1st switch on?

My grateful thanks to everyone who took the time and trouble to reply to my posts and best wishes to you all.

Rich