M25 repair?

dgoodhue · Post by **dgoodhue** » Wed Jun 20, 2007 4:17 am

I was replacing my M25's caps and notice this repair on the back side of the board. I was curious on anyone had any insight to these repairs.

FYI so far 2 of the 3 amps I have replace the caps have shown signs of leaking caps.

vin78 · Post by **vin78** » Wed Jun 20, 2007 4:59 am

I never saw that in the back of my M25...it must have been a circuit board revision. Which series is your M25?

dgoodhue · Post by **dgoodhue** » Wed Jun 20, 2007 5:57 am

Its a Series II

rolandk · Post by **rolandk** » Wed Jun 20, 2007 7:30 am

That was an upgrade. The resistor and cap are snubbers. They go across power supply rectifier diodes and are designed to stop noise. Your circuit board is an earlier one, probably Rev F or earlier. Rev G was the latest and IIRC those components were incorporated into the regular circuit board.

1moreamp · Post by **1moreamp** » Wed Jun 20, 2007 9:19 am

RolandK is correct as usual.
At least they hide the mod on the bottom of the board so it would not look fugly on the topside. The big resistor is pretty unique. I remember adding a couple sets of these to M-44's in there early release models that we sold at the Autophile back in the day. they do reduce diode switching noise issues in the power supply. I even saw this same mod on a Route 66 that I worked on for twisted but they added that mod across the diodes on the topside of the board on that amp, and RTV'ed them together to stabilize them. C

rolandk · Post by **rolandk** » Wed Jun 20, 2007 9:31 am

Cecil is correct as always

M44's do have the same mod as did earlier MS275's.

dgoodhue · Post by **dgoodhue** » Wed Jun 20, 2007 11:02 am

Thanks for the info, it didn't look factory installed to me and I didn't remember seeing it on my older Series I M25. I was thinking that it might a back yard repair.

BTW the board is a Rev D.