MPX G2 "Digipot Test Fail"

[Guitarist]

A friend who used to work at Lexicon gave me one of these cool guitar processors. I'd love to start using it!
It seems the -5 rail is being pulled down from something in that Digipot circuit. I replaced two voltage regulators (in this area) but its still the same.

Anyone come across this issue prior or have any ideas of how to fix this unit?

thanks,

[Steve Conner]

How far down is it pulled?

Say it was 2 or 3V instead of 5. Then you can feel the chips looking for an abnormally hot one.

If it is right down at 0V then the fault is a dead short. The offending part won't get hot because power is voltage times current, and the voltage is 0. In this case you can use a 4-wire ohmmeter or other kind of circuit tracer to track it down. Or you can try the ghetto method, use a high current 5V supply to blow the faulty part up completely.

[J M Fahey]

Did the unit ever work?
Maybe your friend got hold of a returned unit or something.
This stuff is usually not repaired at component level, but by board swapping or even sending a brand new unit to customer.
Delights of robot manufacturing.

[Guitarist]

I just did the feel test and other than two 5V regulators—which are HOT— and one I replaced, no other components seem warm. Good idea guys. The rail is down around -2.5V. I may get my friend to ask for a schematic who said it was working prior. Maybe just send it in someplace or to the great repair guys at Japan Elec here in Vancouver.

Also I pulled audio out via a a 600V cap on an adapted guitar cable, and there is major whine even on some of the preamp ground pads as well as on other places. That is weird.