Ampeg SVT II Pro - help needed

[Roberto Lasco]

Have a Viet one on the bench with no high voltage present; actually power led doesn't even light up (red or green). Tubes are fine; filament voltage is there and so is rectified filament voltage that controls the relay.

I couldn't figure out how the power led is fed: besides ground side, the + for the led only goes to the first pin of a ribbon cable that links to the graphic eq board, which don't have any other connection...
Measuring on the pcboard, led looks shorted, but I desoldered it and it's not (so his supply looks like). Measure odds though; unlike a regular led that reads infinite/voltage drop on the meter, this one shows voltage drop (1.7) on both polarities. Not sure if those multifunction/two color leds behaviour this way.

Anyway I'm kind of lost on where to look at this low voltage supply; any guidance is appreciated, have a deadline on this...

thanks,
roberto

[Phostenix]

Schematics are at the bottom of this thread:
http://music-electronics-forum.com/t6121/

The LED circuit is on the EQ schematic.

[Roberto Lasco]

Thanks ! Shot zeners in low voltage supply. Do these usually fail ? Any need to beef them up ?
It's a shame I don't have those parts right now; I'm itching to test it with those (Fender HR) 1N53538 (16V/5W), but I guess I'll wait till tomorrow...

[dcline]

Ampet SVT 2 pro

I've just acquired one of the amps.
Seems to be working well so far.
Needs the volume pots cleaned. Bias seems ok.
Can anyone tell me if it is typical of these amps to pop when turning the amp off with the standby off?
Shouldn't it have a cap to absorb that?
Thanks in advance

[Enzo]

Many many many many many amps pop or thump at power off.

[crisisat22]

I recall playing one of these brand new at a Guitarget a few years back (definitely a pre-Nam model) and yes, I do remember a loud pop when powering down.