Max 112 bass combo hums

[dak]

D9/D10 probably don't have "values", they are diodes (and don't look like Zeners). Look like a standard 1N4148 to me.

Now we might be getting somewhere.

1N4148... OK. What voltage and milliamp rating would be suitable?

I have tried to contact Peavey multiple times with no results.

Rotor

Ok, a 5-minute search on the Internet gave me the schematics (no idea why I should be the one doing the work instead of you) and those are indeed Zener diodes after all, 1N4744A. From the stuff around them, they stabilize to 15V and are fed through 250ohm from 35V, so they need to be comfortable with 80mA or 1.2W which an 1N4744A isn't (it's good for 1W). So the circuitry relies on other devices to use up part of the power and it is not overly surprising that the PCB looks baked and one of the diodes died. The problem is that with the diode dead, the opamps don't get stabilized power supply and it is to be hoped that they survived. At any rate, should be good for some hum and noise.

[dak]

Any idea what could have caused this diode to die in the first place?

Rotor

The way it looks to me, optimistic design may be partially responsible. Particularly so if some opamps were upgraded to ones with less quiescent current.

[Rotorranch]

Well I finally got ahold of Peavey, and Chris sent me the schematics, and is sending the diodes... he also told me to check a couple other things to check... all of which seemed to check out fine. I'm hoping replacing the diodes will get this amp off and running again.

I hate stuff that doesn't work correctly.

I'll update as soon as I get the parts.

Thanks y'all.

Rotor

[dak]

Well I finally got ahold of Peavey, and Chris sent me the schematics, and is sending the diodes... he also told me to check a couple other things to check... all of which seemed to check out fine. I'm hoping replacing the diodes will get this amp off and running again.

I hate stuff that doesn't work correctly.

Just to put some perspective on this: this kind of post-resale care is kind of unusual for any company to provide.

[Rotorranch]

Well, Peavey sent me the parts. I changed both D9 and D10, and it seemed to be OK. Reinstalled the chassis to the cabinet, and it blew the D9 Mdiode again! I replaced it with the good diode I had removed, and the hum was gone, but I have no output to the speaker.

There is a little bit of hiss if I crank it up, but no music.

I have no idea what is wrong with this amp! I parked it for the time being, until I have more time to fool with it.

Rotor

[wingbean]

Just bought a 40w Max 112 at a high school auction, brought it home, powered it up... Same problem. No guitar, only hum. Opened it up to see the same burnt area with D9, D10. Haven't tested them yet. None of the caps are bulging. Found replacements on Amazon, matching part numbers on the schematic.