Yamaha M508 Repair and Mod Project

[DrummerMic]

Hello!

Recently purchased a M508 and right off the bat need to fix the L PGM; not working/ no audio output.
1.) What is the best way to go about troubleshooting this?
Run a signal through the board and track it? I do not think I have the equipment to do it; unless it just takes a multi-meter???

2.) Looking to mod Direct Outs and I am wondering about converting the SUB Ins to Channel Inserts? I assume its possible but have no idea
what all would be involved. If its too complicated....it was just a thought.

3.) Everything besides the PGM L works/sounds great but I have also read that re-capping old gear like this is a smart move. Would it be worth the effort or....if it aint broke, dont fix with it?


Any help or insights would be much appreciated!!!

If there is anyone out there that can help, it would be most appreciated! Thanks!

 

[Ike Zimbel]

In answer to ONE of your questions, I wouldn't bother to re-cap it. Yamaha used good quality, long lasting capacitors. I tested a lot of capacitors that I changed in a PM-1000 this year (at the owner's request) and I didn't find a single one that was off spec.

 

[DrummerMic]

Thanks Ike!
Yeah, the caps look like they are in good shape or at least nothing is blatantly blown out.
I am currently trying research testing the caps and I know I can do it in place by do not have the
right meter.

I hope that the problem with the Left channel is just a bad cap. Fingers crossed!!!

 

[Ike Zimbel]

Thanks Ike!
Yeah, the caps look like they are in good shape or at least nothing is blatantly blown out.
I am currently trying research testing the caps and I know I can do it in place by do not have the
right meter.

I hope that the problem with the Left channel is just a bad cap. Fingers crossed!!!

I doubt that it's a cap, but it could be... Common issues with phenolic circuit boards are cracked / broken traces, particularly around connectors, so you could look for that. It looks like there may be enough cable length that you could (carefully) swap headers between L&R sections and see if you can narrow down where the fault is occurring. I think the Black/White/Orange connections are the faders, so you could swap those and see if you have a bad fader in PGM-L. You could also try rocking that 47/25 cap next to that connector and see if it has a bad solder joint. Gently rock it from side-to-side (the white negative terminal is a "side"...all caps will rock in the top-to-bottom orientation, which will eventually break the leads off, so don't). If it has a soldering issue, one lead will move in-and-out of the board.

 

[DrummerMic]

After further inspection, I found that it is the R PGM that is having the issue. There is a loud hum (constant) and there is audio, it is just very quite. Would indicate a bad ground somewhere?
I also found what looks to be corrosion around TR13/14/5/&1 on the DC C. Board. Is that normal or
could that be a potential issue?

Ike, you are correct about the Black/White/Orange connections and I "rocked" the caps but everything feels solid. Swapped C7 & C9 to check faders; meters move and faders fade.
Any thoughts?

 

[Ike Zimbel]

That's thermal compound, not corrosion and it's supposed to be there. It's a bit messy, which indicates that transistor may have been replaced at one point, or at least messed with. Hum is more likely a failed component than a ground issue.

 

[DrummerMic]

That's thermal compound, not corrosion and it's supposed to be there. It's a bit messy, which indicates that transistor may have been replaced at one point, or at least messed with. Hum is more likely a failed component than a ground issue.

Ok, it seems as though the issue is just with the R PGM.
The Channels, Sends, and L PGM sound great; nice and clean imho but
you can hear the hum in the headphones as well....

If the issue is with the R PGM then would it make sense to focus
on the LA C board or could that issue be caused from any component
anywhere on the board failing?

Just am wondering if there is some electrical deductive logic a more
experienced person would use to troubleshoot.
You can probably tell I am new to this!

Thank you again Ike for your insight!