Help! Mesa Nomad 45 Reverb Failure

[master-t]

Hey all, I've gotten some great advice here over the years on modding a Sovtek 50, fixing a Crate Stealth, and Ampeg VL502. Now I've got this Mesa Boogie Nomad with a reverb that don't work!

Tank is fine, checked it with another amp. Return is working as it buzzes when removed and finger-tipped. The driver appears to be the issue and from what I can tell from the schematic, it's an op amp. Anybody had one of these issues already and can tell me "Yep, replace op amp and R437" or whatever? if not, any guidance on troubleshooting and repairing is much appreciated.

Schematic is:
http://www.schematicheaven.com/boogi...ie_nomad45.pdf

Looks like some hand drawn mods/updates to reverb section which are kinda throwing me off.

Thanks!

Todd

[Twist]

I would first measure the input and output of the tray to see if it's open on either side. An OpAMp driven tray will have a higher impedance on the input than a tube driven tray. If you have the correct tray and everything looked ok there, I would check my cables for continuity and corrosion on the plugs and jacks. Then I would probably replace the OpAmp that drives the tray. Since you can hear hum by touching the return jack, it seems likely that OpAmp is ok, but you never know. I see a input selector for the input of the reverb driver, that may be the problem.

[master-t]

Hey Twist, thanks for the reply. Yeah, did all that. Measured tank, one high, one low, and checked and even replaced the cables. I reckon' I'll replace that op amp and see what happens. I think I'll scope the input and output first to see what's coming and going but it seems that's the next step...thanks for the insight.

[52 Bill]

You could try sending the signal from the reverb drive cable to the input of another amp, to see if there is a signal there.

And as Twist noted, the reverb signal is selected via a relay. Be sure to check the relay and the switching supply circuit.

[master-t]

big 10-4. I'll check that relay post haste!

Thanks fellers!

[master-t]

OK guys, I replaced the op-amp...no dice

I was thinking about bypassing the relay, but I'm not sure which one it is. The guys at the mesa sight don't seem to be too technical (or the good ones aren't chiming in) and I've had much better luck over here.

There are several relays on the board and there is one close to that reverb op amp driver...I'm starting to get frustrated. HELP! LOL

Thanks,

Todd

[52 Bill]

I was thinking about bypassing the relay, but I'm not sure which one it is.

If you look at the schematic the reverb relay is probably marked RY#. Is the board marked as well?

[master-t]

there are 5 or so relays in there. board isn't marked well at all.