Mesa Boogie Maverick repair blues

[six el six]

I need some help troubleshooting a Mesa Maverick.

All voltages seem to be fine on the tubes including phase inverter, preamp, and power. It's the switching that's not working right and I know very little about switching.

Both channels put out very little volume (approx. 5% of normal) UNTIL I plug into the effects send 1/4" jack with a jumper cable

THEN the lead channel works great. It sounds good, loud, all tone controls work, master vol. works, as does the output volume. It doesn't matter whether  I connect the return to the send or just leave the plug dangling while only plugged into the send jack. I still get full power from the LEAD channel in either condition.

When you switch to the rhythym channel you get next to nothing, vol. drops 95% from the LEAD setting and sounds the same as when there is no plug in the effects SEND jack. The bright/fat switch also appears to do nothing regardless of where anything is set.

I should reiterate in regards to the quality of the LEAD channel with a jumper cable plugged into the effects SEND jack; it sounds very good.

Schematic attached and thanks for any help in advance. I definitely need to learn my switching circuit theory.

[plexi50]

Is the 25k FX return pot good? Dirty or bad FX inputs?
Can you hear a relay click when you switch between the rhythm and lead channels?

[six el six]

Someone has removed the tops of two of the three relays in this amp and I can see both "customized" relays actuate. I don't know what the third one is doing. I'm also not familiar with the best way to test relays. Any advice?

The fx return jack is clean and the 25k fx mix potentiometer is fine as well.

I've attached a gut shot.

[phsyconoodler]

Step one: replace the FX loop jacks and try again.

[PRR]

The symptoms do not make enough sense.

What is the history? Has it always been yours? Was it working fine and then got sick? Or does it have a secret past?

Busting-open the tops of the relays is a very strange thing. I'd wonder what OTHER strange things may have been done to it.

I'd be looking for bad jacks, cracked or mis-modded PCB. This could come down to a joint-by-joint re-validation against the incomplete schematic. The amp may be worth it, but that will be a LOT of time.

Or leave a plug in it and enjoy the clean channel, with fuzz in front if needed. However I do not see why the plug "fixes it" and wonder if the fix might undo itself on the next good bump.

[jojokeo]

RV1 a&b is having issues. Send jack needs a look at too - this is odd behavior. The lead channel operates because it's in the normally closed positions of RV1. Rhythm channel is dependant on the relay's activation and good contacts of a & b for signal to get to the pi stage. This is also why you don't get tone or fat controls related to this channel. Those relays on the board look to have cracked by heat, time, and vibration. They should be replaced either way you look at it.
To test a relay, it may be best and easiest to remove from circuit but doesn't always have to be. You need to test coninuity of normally closed pins, then activate it and test continuity on normally open pins. Good contacts should show no resistance or the same as when you touch your probes together.
The only other thing is LDR4, that's going to short signal to ground when closed.

[six el six]

What is the history? Has it always been yours? Was it working fine and then got sick? Or does it have a secret past?

I'm repairing this amp for someone who was not treated fairly by someone who was supposed to be getting it repaired before. He told me how much money he'd paid for what clearly is NOT a satisfactory repair so... I think he said it came off of evilbay before he got it.

I'm going to work on it tomorrow evening. As usual, thanks to all.

[mresistor]

I found this link with pictures of a maverick disassembled somewhat, might be useful to you. What I see is that your relays definitely don't look good (as already noted), in comparison they look pretty bad; and I wonder if they were damaged by heat. Or if a human chipped away the top of the cases and if so, was it for troubleshooting? I agree with above, I think the relays need to be checked out, see if they are switching properly and contacts are making good contact. Looks to me like you will probably have to pull the board up to unsolder them for removal. I wonder what the failure rate of the relays is, or if there is a failure history. Guess MB would know, but I wonder if they would tell you.

http://trentstuff.com/1993-Mesa-Boogie-Maverick-4x10-Fuse-Problems-Inside-Board-Photos/Mesa-Pics.html

Also, what's the black goop on the 30uf elytics? maybe some have been replaced at one time? Compare to the pic in the link I provided.

[mresistor]

Ok if the pics in the link I posted are of the same model amp, I'm thinking your amp might have had some pcb trace damage, compare the wiring of the 30uf filter caps on both amps. Yours has some wires going right to the cap leads. Also I notice the 220uf caps on the other end of the board have been replaced with Illinois caps, but they could be factory installed. If they were replaced...why? I think I'd pull up the main board and have a look for sure. Probably other things going on too.  I'm thinking a rectifier failure or power tube failure in the past that did some damage. Or a shorted load maybe?

[six el six]

@mresistor

The amp came to me with the tops of the relays "chipped" or "cracked" off. The two that are disfigured appear to function though I don't have an understanding of relays that is satisfactory to me as of yet. Suffice to say they can clearly be seen actuating.

If anyone doesn't think I should unscrew the pots frpom the chassis and pull the board up for an inspection of the underside of the pcb AND to facilitate a more responsible removal (than previously done) and out of circuit inspection of all suspect components PLEASE LET ME KNOW. Disassembly should commence in the next couple days or so.

I should also probably make clear that, yes this amp came to me the way it is in the gut shot.

[phsyconoodler]

you need to measure all the voltages and address the effects loop issue before going any further.You said the jack was clean but there are two jacks and the low volume symptom you describe leads me right to those jacks.Poor contact = low volume and the fact you get something when plugging into one tells me there still is an issue there.
  Try putting a patch cord into the in and out jacks of the loop and see what happens.
I'm seeing lots of stuff on that board that's been mucked with.

[mresistor]

"I'm seeing lots of stuff on that board that's been mucked with."

like the 220uf filter caps on the other end of the board have added wiring...  as well as other things.....

[PRR]

> anyone doesn't think I should unscrew the pots frpom the chassis and pull the board

On one hand, it IS a fine amp if you stick a plug in it and love clean.

OTOH, the plug-trick is dubious and the amp should be so much more.

It begs for a full look-over and restoration. Whether you have the time and energy is another matter.

As PCB amps go, this is not the worst disassembly around. (There's other amps, if they were as mystery-sick as this, I'd just list on eBay "for parts".)

[Jack1962]

replace the "chipped" relay's and test , efx send jack is bad replace it as well , switching problems are common with Mesa amps.