Rotary pot issue on Pioneer amp

Chelon

Dusted off my old amp after 12 years in the loft. It works but one issue.

There is no sound from one channel when the balance knob is central. However when you slowly rotate it there is perfect sound at a couple of "sweet spots" - but when you set it to centre, nothing. Other channel is fine always.

I sprayed cleaner in but it didn't make any difference. It's not crackly like you would expect from a dirt problem but I'm assuming it is some issue with the pot. If so is there anywhere in Dublin I could buy one? It looks like this:-

FullSizeRender.jpg

Effects

I think you need a better picture. The only thing in focus is the screws.

Chelon

Hokay - updated now

Chelon

Does anyone know if something like this would be likely to be an off the shelf item anyway, or would it be a Pioneer-designed item?

If the latter then I'm probably snookered

Kalman

Try spraying "Switch Cleaner" inside the pot on. [not outside] A tin of cleaner with an attached long nozzle. I find "Super Servisol" an excellent cleaning lubricant.

Check the part number against this. You can just search for the component part number anyways.
I've no idea if this is suitable.

http://www.ebay.co.uk/itm/Pioneer-Potentiometer-DJM-600-Gain-Trim-Channel-Booth-DJM-3000-Gain-DCS1054-/161319356670

Probably just pitted carbon track.

Lots of spares here:
https://www.soundbasemegastore.com/spare-parts/pioneer/

biketard

Where were you spraying the cleaner? You really need to make sure it goes inside (from the look of that ebay link, you'd need to at least try to spray a bit in the gap around the bottom of the pot and hope enough bounces up onto the tracks). That pot's going to be a bit of a pain to unsolder if all those pins are soldered in and I'd certainly be trying the old cleaning approach first. Sometimes it takes a couple of goes (and then rotating the pot fully back and forth) before it has any effect.

biketard

biketard wrote: »

That pot's going to be a bit of a pain to unsolder if all those pins are soldered in

Two soldering irons.

Kalman

Chelon wrote: »

Dusted off my old amp after 12 years in the loft. It works but one issue.

There is no sound from one channel when the balance knob is central. However when you slowly rotate it there is perfect sound at a couple of "sweet spots" - but when you set it to centre, nothing. Other channel is fine always.

I sprayed cleaner in but it didn't make any difference. It's not crackly like you would expect from a dirt problem but I'm assuming it is some issue with the pot. If so is there anywhere in Dublin I could buy one? It looks like this:-

FullSizeRender.jpg

However, If, after all, you decide that you need to replace the potentiometer; you must remember, removing components and re-soldering replacements from a circuit board is quite tricky.

You would need a "solder sucker" or "solder-Braid" and the right sort of iron, [not an incinerator] after all you don't want cook the device. These are not the sort of items that you would have at hand.

Chelon

Sir Liamalot wrote: »

Two soldering irons.

I'm aware of basic soldering technique but how so with 2 irons....?

Chelon

biketard wrote: »

Where were you spraying the cleaner? You really need to make sure it goes inside (from the look of that ebay link, you'd need to at least try to spray a bit in the gap around the bottom of the pot and hope enough bounces up onto the tracks). That pot's going to be a bit of a pain to unsolder if all those pins are soldered in and I'd certainly be trying the old cleaning approach first. Sometimes it takes a couple of goes (and then rotating the pot fully back and forth) before it has any effect.

So looks like I'll need to unsolder it then spray from the board side? I was spraying from the other side.

Chelon

Chelon wrote: »

I'm aware of basic soldering technique but how so with 2 irons....?

Dual wield them. One per hand. Hard to do SMD work with just one.
You could run the tips sideways against the pins and gently encourage them out.

Or if you want to commit; cut the legs off the pot desolder one by one and try to clean as much solder off the holes you can.

I doubt it'll be any easier to clean if you desolder it. Cleaning won't help a worn out track.
Maybe cleaner + compressed air or just compressed air might do the business.

Chelon

Seen a tip on another forum that looked feasible - since the balance control is almost never used, just bypass it.

Anyone got any idea how you'd do that? Could be a quick fix...

Not with a 7 leg pot.

You'd have to figure out what leg does what and use fixed resistors because it's probably configured as a potential divider.
0 on the dial is 50% on the wiper and it's probably logarithmic too.

Unless you have a balance bypass switch on the amp.
I think it'd be actually easier swap the pot.

The bodge fix is use two channels L and R and mix them stereo with a lead or aux input..not much point really since you could just use stereo on the second channel.
Or just make a dirty mono to stereo lead.

knickerbocker

Chelon wrote: »

Dusted off my old amp after 12 years in the loft. It works but one issue.

There is no sound from one channel when the balance knob is central. However when you slowly rotate it there is perfect sound at a couple of "sweet spots" - but when you set it to centre, nothing. Other channel is fine always.

I sprayed cleaner in but it didn't make any difference. It's not crackly like you would expect from a dirt problem but I'm assuming it is some issue with the pot. If so is there anywhere in Dublin I could buy one? It looks like this:-

FullSizeRender.jpg

What's the model of the amp OP?

biketard

Chelon wrote: »

Seen a tip on another forum that looked feasible - since the balance control is almost never used, just bypass it.

Anyone got any idea how you'd do that? Could be a quick fix...

Not a bad workaround. If you can wait till after the weekend, I'll look into that for you. Seven pins are probably 3 for each side and maybe one just to ground the metal parts of the pot (educated guess--I may be wrong).

You sure there isn't a hole in the circuit board under the pot where you can spray some cleaner in from the other side? A thoughtful board designer might've designed it with maintenance in mind (though I wouldn't put money on it).

Again, if you can get a spray with a straw-type thing on it, you may be able to just hold it against the thin gap and spray hoping that it bounces up inside the pot. I'd try one of the side edges.

Chelon

knickerbocker wrote: »

What's the model of the amp OP?

Pioneer A-502R

Johnboy1951

If you cannot find a parts list for that amp I would be inclined to do the following (or get someone to do it) ....

Cut out the existing faulty pot and clean up the PCB holes ready for a replacement.

Measure, in so far as possible, the values of the pot/s and draw out a wiring diagram with the pin out and values measured.

Buy either or both of the following
https://www.soundbasemegastore.com/21193-pioneer-djm-300-500-trim-potentiometer-dcs1034.html
https://www.soundbasemegastore.com/21197-pioneer-djm-600-3000-eq-potentiometer-dcs1053.html
(they might even be the same part for all I know)

Compare the values and pin out of the replacement with the drawing.
Adjust, if necessary, the value of the replacement, by adding resistors ... in series or parallel as required.

As it is the balance and unlikely to be used very much, limiting the range should not adversely affect things.

Fit the replacement.

The amp would want to be worth the effort

Johnboy1951

Johnboy1951 wrote: »

The amp would want to be worth the effort

knickerbocker

Two possible solutions I can see:
1) Press the 'Direct' button, thus by-passing the balance pot, or
2) It's a 250kΩ pot, maybe replace it with the 220kΩ pot in the link below, though, this will require adding a bit of wire to the legs as they are not in line:

http://cpcireland.farnell.com/omeg/pc2g16eco220ka/pot-dual-gang-lin-220k/dp/RE04434

Schematic.

It's a two track pot with two wipers. One pin possibly not wired...hard to see on the pdf.

VR301 = ASC1052 Pioneer Part

Chelon

Sir Liamalot wrote: »

Schematic.

It's a two track pot with two wipers. One pin possibly not wired...hard to see on the pdf.

VR301 = ASC1052 Pioneer Part

That's fantastic, a big help. Only snag is I don't think they ship outside the US. This looks hopeful though, I'll call them tomorrow:-

http://www.pioneer.eu/uk/faq/99999/1479/page.html

Chelon

Also as the pot is referenced by what looks like a Pioneer part number, I'm presuming it wouldn't be available at RS or suchlike? I dropped in there and they said to bring the board in and they'd take a look but I'd say it's a long shot..

Johnboy1951

Only place outside USA I found the part ..... Hungary .....

http://www.alkatreszbolt.hu/szabalyozhato-ellenallas-potenciometer/csavaros-trimmer-potenciometer/pioneer-acs1052-szab-lyozhat-ellen-ll-s.html

knickerbocker

Chelon wrote: »

That's fantastic, a big help. Only snag is I don't think they ship outside the US. This looks hopeful though, I'll call them tomorrow:-

http://www.pioneer.eu/uk/faq/99999/1479/page.html

Might I suggest you remove and check the pot before ordering a new one! Just to confirm this is the problem..... t'would be the logical thing to do?

US seller $15 to ship. Duty free on spares.

Easiest way to test the old pot.
According to your photo orientation

Track 1 is pin 1 (top) and pin 6 (second from bottom), corresponding wiper is pin 4.
Track 2 is pin 2 and pin 5 with wiper on pin 3.

To test it (you may have to take it out of circuit for depending on setup) just stick a multi meter set to resistance on one end of the track and the other probe on the wiper and turn the pot.
You should get an incremental or decreasing resistance. Repeat for 4 track pins. If you get an out of limit reading either the track/wiper is bad or you've a broken connection.

Pin 7 might be earthed or not wired.

biketard

Sir Liamalot wrote: »

Easiest way to test the old pot.
According to your photo orientation

Track 1 is pin 1 (top) and pin 6 (second from bottom), corresponding wiper is pin 4.
Track 2 is pin 2 and pin 5 with wiper on pin 3.

To test it (you may have to take it out of circuit for depending on setup) just stick a multi meter set to resistance on one end of the track and the other probe on the wiper and turn the pot.
You should get an incremental or decreasing resistance. Repeat for 4 track pins. If you get an out of limit reading either the track/wiper is bad or you've a broken connection.

Pin 7 might be earthed or not wired.

This is the info I've found too. Looks like pin 7 is just a dummy pin. To bypass the control you'd need to get your hands on four 50Kohm resistors. Disconnect the pot, then on the board itself put one resistor from pin 1 to pin 4 and another from pin 4 to pin 6. Also you'd need a resistor from pin 2 to pin 3 and another from pin 3 to pin 5. (All of the above assumes it's a linear pot). It'd be just as easy (easier actually) to put in a new pot.

Also, if you get as far as removing the old pot, you'd have a good chance of being able to get it working again by spraying cleaner into the back of it.

I'd be tempted to unsolder the retaining clips on either side of the pot and bend it up just enough to get cleaner in there.

whizbang

I found a bunch of very similar pots on a Vestax mixing console, they are Alps manufacture, and have the first few digits of the part number printed on them.
Sorry i can't remember!! but i did find the exact part on their website, with diagrams.

They are very well sealed, almost impossible to get fluid inside. As a mechanical part they do suffer damage, but usually the shaft gets pushed sideways, almost always breaking the soldering before damaging the component.

Are you sure the solder joints are all perfect?

Chelon

whizbang wrote: »

I found a bunch of very similar pots on a Vestax mixing console, they are Alps manufacture, and have the first few digits of the part number printed on them.
Sorry i can't remember!! but i did find the exact part on their website, with diagrams.

They are very well sealed, almost impossible to get fluid inside. As a mechanical part they do suffer damage, but usually the shaft gets pushed sideways, almost always breaking the soldering before damaging the component.

Are you sure the solder joints are all perfect?

I unsoldered the pot from the board and tested as most helpfully described by SirLiam - there does indeed seem to be a couple of dead spots in the range - tried cleaning but as you say it's a fairly well sealed unit. I'm going to try to get a replacement now....