MP-2 After the noise mod - Spanky Clean is distored . . .

[MarshallJMP]

Anyway that 38V doesn't look good,could be that the LM337 is busted.This could be the reason of the hum.My guess is also that U205 and U207 are busted (OPA2604A),one of these is used by the compressor.Now i suggest not using the mp-2 until this problem is fixed.It also could blow up your input section.

[W.Laturno]

Ok - here we go:

U901 (LM337T)  Pin 2 input measures -38.9vdc and pin 3 output measure -38.6vdc

U906 (LM317T)  pin 3 input measures 38.7vdc and pin 2 output measures 23.7vdc

I seem to remember we discussed these U205 and U207 before.....
here is what I measure now:
U205 pin 4 -38.2vdc     pin 8 +23.6vdc

U207  pin 4 -38.3vdc    pin 8 +23.6vdc

[MarshallJMP]

Ok seems like the LM337 is busted so replace it,also replace those 2 OPA2604A's just to make sure.

[W.Laturno]

So, last night I installed a new U901 (LM337 )  . . . had some trouble fitting my iron in the top side to insure the joint was soldered there ( it's a tight fit )

I also believe C916 was loose so I took it out and re-did it . .

I had not received the new OPA2064A's . . but I wanted to see if indeed now I would get -38vdc into U901 and -24vdc out, but it is still -38vdc out...


Perhaps I had too much heat on my iron and destroyed it while installing....(?) it is an adjustable temperature iron and I believe I have the dial set to around 350°C....

I am just wondering if maybe D901 ( across the in/out  pins 2/3) of U901 is bad or something.....it just seems that the adjusting part of that circuit is not pulling the voltage down....or it is quite possible that during the noise mod, a certain cap has a bad connection (C903,4,or 5 ??)....this is possible, but I am grasping at options here...

[rnolan]

Hang in there Will, you'll get it done  :thumb-up: , I get what your saying regarding the adjusting part of the circuit not pulling it down, that's where my thoughts would go in the circumstances also, I'm sure MJMP will throw some light on it..