Please help identify this terrifying noise?

[JW]

I have this noise on a couple channels on my console. PLEASE TURN DOWN SPEAKERS. It's horrible on my monitors. Can't figure what it is. Does it sound like bad contacts? A cap not working? It's extremely intermittent so very hard to catch. Channels are recapped, faders cleaned, switches de-oxidized (though switches might still be the culprit, but oxidized contacts don't make noises like that do they? Horrendous, not just normal crackly contacts)

Anyway, console is Yamaha PM2000. Schematic attached. Sound file here. https://youtu.be/3myYOalNcvU

 

[JW]

PM2K schematic part 2

 

[NOON]

I've just been doing some restoration work on some PM2000s and had a couple of channels with the same issue. It was one of the opamps in the channel, usually the first. If you don't have an external testing rig, pull out a few channels next to the offending ones so you have access to the board, trace the signal path through with an oscilloscope and see where the noise starts.

  Luckily we had a bunch of spare channels to steal parts from. If you don't, look for the IC adapters from Brown Dog to replace the 'inline' HA type opamps with more modern opamps (make sure they can take +/-24V).

 

[JW]

Yes, I've actually already done swaps from the HA chips to opa604 mounted the same way as this fellow: https://flyingeyepro.files.wordpress.com/2014/09/img_3677-0.jpg

Two of these old Hitachi chips are used in the eq and my channels now have inductive eq modifications for the mid bands associated with those two Hitachi chips. So they are pulled. There are two more associated with the HP filters which I've left, and the other four are replaced with opa604.

Good to hear that you've experienced the same sound though (not for you, but I'm glad for a pointer) So now I'll focus more closely on the opamps.

I also tried swapping the line amp DOA for another 80100. Could have replaced bad with bad or an error in one or two of my 604 replacements.

Anyway, it WAS  one of the Hitachi opamps on more than one occasion? (rather than the DOA's?) Or did you mean the first DOA which is bypassed in line amp mode? I didn't try swapping that one as it's for the mic input and bypassed with low switch settings.

 

[NOON]

Had that kind of noise on a few channels, but I think only one was an input channel, the others were master channels. If you've checked / replaced all the HA opamps then it'll probably be the 80100, they fail a lot more often than the 80200s. It was the input / summing HA opamps on the master channels making all the noise.

 

[patosandia]

hi!!! Resurrecting old thread, i´m having the same problem right now, what did you end up doing?

 

[JW]

It's an opamp most likely. You can probably tell if it's a DOA by when/if it clicks in. If you turn up the input switch to kick in IC1 and it's fine before that, it's IC1. If it's freaking out at +4dB setting it's probably IC10. I don't think I've had many at all of the HItachi's go bad. Maybe one or two. But plenty of the 80200/80100. My current favorite replacement is the APP992.

You can always do the speaker trick, with a capacitor between the + and the probe. If the eq and high passes are bypassed, and it's still there, probe the out of IC1, IC2, IC5, IC6, IC10 until you find it. The bitch is, they're often intermittent. You're blessed if it is consistently misbehaving.