Roland kc-300 how do you?

[nosaj]

How do you guys clean these kinds of pots? are they sealed never run across them before.
nosaj

[The Dude]

I'll sometimes try working deoxit right down the side of the shaft and let gravity do the rest. Of course you have to orient the chassis so the cleaner goes down into the pot. It takes a little patience. If that doesn't work, you have to take the pot apart and do a more thorough cleaning or replace it.

[Enzo]

I find I can usually squirt some cleaner on the rear wafer and work the pot. SOme of the goo makes it to the insides. Orient the chassis so the pots face down, so anything you squirt will pool a bit on the rear of the pot.

[The Dude]

Yep. Just about any crack or crevice will do as long as you remember to orient the pot so that gravity takes the cleaner to the wafer contacts. It doesn't really take that much cleaner to do the job.

[g1]

You can try, but in general they are considered 'replace only' parts. I usually just quote for replacement. This is the kind of thing that makes something like a mixer not worth repairing when considering replacement cost of the whole unit.

[nosaj]

I was just asking since I had never seen that kind before. The problem with the amp is that it sounds bad an has a warble to the sound. The power rails are running a 10v difference between -+rails which is creating the warble in the power amp. Sounds fine through the headphone jack.
Roland KC-300 Power Amp Schematic.pdf
Roland KC-300 Preamp.pdf
nosaj

Looking at recapping the power supply and see how it goes from there.

[DrGonz78]

I was just asking since I had never seen that kind before. The problem with the amp is that it sounds bad an has a warble to the sound. The power rails are running a 10v difference between -+rails which is creating the warble in the power amp. Sounds fine through the headphone jack.
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nosaj

Looking at recapping the power supply and see how it goes from there.

Post measurements of voltages at both sides of Q1 & Q2. Just curious which side has lower voltage and what the low voltage supplies measure.

[nosaj]

Already in the middle of recapping power supply. +40vdc and a -31vdc is what I had written down . Should be done in another 20 minutes or so.

nosaj

[drewl]

Also sometimes you need to push the tabs on the back in GENTLY to re-tension the pot wafer.

[nosaj]

Post measurements of voltages at both sides of Q1 & Q2. Just curious which side has lower voltage and what the low voltage supplies measure.

Before recap the LV was a -+15vdc HV was what was off.
Recapping the Entire Power supply solved the issue of the warble. Amp sounds fine now.
Thanks all.
nosaj

[J M Fahey]

The low voltage rail must have had horrible ripple, real dry caps.

Not audible all the time because well designed modern amps have high supply ripple rejection (PSRR) but as soon as it starts demanding significant current, PS can not supply clean voltage/current and ripple appears modulating signal.
Again, not audible by itself.

[nosaj]

Also i just love it when I have everything already on hand to do a repair. Even though I'm just a hobbiest repair guy. I only see maybe an amp or 2 every other week. But i sure love being able to turn something around in a day. just hope the clients don't get too used to that . Cause this can never be a full time job it'll loose that magic an become that dreaded word "WORK".

nosaj