Yamaha CP30, troubleshooting output noise

[WhinyLittleRunt]

And another one... lol

I just picked up a very decent CP30 on CL last night for cheap. I missed my old one, and even though I sold it to a friend and still see it regularly, I'd been wanting one again for sentimental reasons (not sure why). So, I have another now.

It was cheap because the seller noted that it has a bad connection in the input jack area, and if you jiggle the controls you can get it to play. Here's what I'm finding so far... it gets power, and has output. The volume pot is very dicey. It cuts in and out badly, not sure if it just needs a really good cleaning or replacement. At first I was finding that only the first set of voices worked but not the second, until I messed around with the volume knob and suddenly the second set appeared. But it almost sounded as if it was missing some notes in the middle octave, and not consistently either. The other thing is that the output is super noisy, like washy... my old one was a little noisy on the output but nowhere near the level this one is... And especially if you just turn on the 2nd set of voices and not the first, if they're not sounding, you still hear the loud washy output noise.

So I popped it open and it was like a weird nostalgia that I remembered but sort of didn't... It was like remembering the line or a scene from a movie a certain way and then seeing it again years later and it's similar but different... I had forgotten how many g-dammmm parts are in this thing!

Maybe I'm looking at a power supply recap? Definitely going to unmount the board with the volume pot and give it a good flush with cleaner and see where I'm at after that. But if anyone has and repair tips on the CP30 I'd love to hear...

[sam]

if you have a signal tracer you can check the output of the dividers....follow the signals from the source until you get the hiss....maybe worth taking the pot apart and refurbing it.
always worth recapping a power supply but i feel the hiss may be somewhere else...

i also have a question....does the decay work without a pedal connected...?

[WhinyLittleRunt]

Yes, the decay controls work. They don't act as a sustain like a sustain pedal would, they are like the decay in an ADSR on the note itself. But yes, it works.

I opened it all up, got the pot board disconnected and de-oxed all the pots. Working better now, still hissing loudly. I know my previous one was a little loud too but not like this. Also, the other two problems which may help lead to the issue, is that 1) I have 3 missing notes (or very VERY low volume on them, barely audible) in the middle octave, only on the second piano voices. They work fine on the first set. That makes me think a failing chip... I took the contact board for that section out and examined it, it's hard to tell what does what because it's just a bunch of resistors and caps, 24 of each to be exact (I'm guessing that's for a 12 note section, 12+12 for voices 1 and 2). Anyway, here's a closeup shot of the section that has the 3 failing notes:




So, i'm going to assume the custom Yamaha YM252 and YM253 chips are the divide down chips...

Also, when you first fire up the keyboard, voice 2 doesn't work until it "warms up" and if you're holding down the keys you can actually hear it ramp up and start working....

[WhinyLittleRunt]

Here is a quick video of the issue- I'm actually activating the key contacts by hand to show the difference between section I and II.

[Dr. Phibes]

Oh wow, I had a chance on one of these last year but I changed my mind. Kinda glad I did now!

Looks like it uses a lot of tantalum caps in what I assume are the individual keying circuits for each section. Worth replacing the six associated with the dead keys and see if that helps.

[WhinyLittleRunt]

This is where I'm currently at, after replacing 4 output transistors on the questionable card with the 3 notes that are very low/almost non-existent. Still have the problem; don't know that it would be a cap issue for the keys because it would mean that, since these are the first 3 keys on that card, that 2,4 and 6 tantalum caps have gone bad simultaneously, where the remaining notes across the keyboard play fine. Although there's no question it's worth trying. It just doesn't explain the other issue, which is the "warm up" procedure where in Piano II, when you first turn the unit on the keys from the top octave ONLY down to board g4 sound, and nothing else lower than that, until about 15 seconds or so later and that board starts to sound, then you go down another octave and they're still not there and THEN all of a sudden the piano comes crackling in, like it was warming up. Now it works, aside from those 3 keys.

It's been suggested that I take the board out and move it down a couple octaves and see if the problem follows the board. I'm fairly certain it does, and if that is the case I'm really thinking I'd need to source one of the proprietary divide-down chips because all the board components across all the boards change slightly; assuming because of the octave being higher or lower, etc. I'm hesitant to move the board as it is a ton of work and all of the wires are wrapped and soldered to terminal posts.

I chatted with Yamaha parts support and they almost laughed at me for asking for such an old part, but I read somewhere someone needed one and they actually had it, so who knows...