Show posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Show posts Menu

Messages - markorock37

.2V? My cheap meter probably.
Finally had a chance to get back to it.
T4 Pin 1 -37.3v
       2 +33.9v
       3 -37.8v
T5 Pin 1 +0.6v
       2 +36.2v
       3 +28.6v
T6 Pin 1 +33.9v
       2 +34.1v
       3 +33.7v
Amp is still on dim bulb tester
T3 pin 1 goes to C4
T3 pin 3 goes to R7
So that checks out as well. It would sure be handy if Marshall gave us some voltages and a board layout.
D4 cathode goes to pin 2 of T5
R42 goes to pin 3 of T5
That checks out according to the schematic.
Actually looks like both have CBE pinouts
So T3
c -40.1v
b -40.6v
e -40.6v

c 31.4v
b 39.0v
e 0.6v

Is it possible the new ones dont have the same pinout as the originals?
Well shoot. I was assuming the same pinouts as T1 and T2. Here it is corrected.

T3 E -40.6v
   B -40.6v
   C -40.1v

T5 E 0.6v
   B 39.0v
   C 31.4v

T3 pins 1,2,3=C,B,E
T5 pins 1,2,3=E,B,C

T3 E -40.1v
   B -40.6v
   C -40.6v

T5 E 0.6v
   B 39.0v
   C 31.4v

I'll get some pics up when I can, I'm out of town for a couple days. Had time to snag some voltages before i left.
Well, I've replaced T1 and T2 as well as D1. Still reading pretty much the same voltages. At this point, all transistors have been replaced in the amplifier portion. I hate to deem this unit a loss but I am leaning that way as it was quite a mess with the traces from prior techs. Im 99% sure I have all the traces repaired correctly.
I don't see 2SA872 on Mouser, is KSA992 a good sub?
T4 E to B  0.3V

T1 E 0.6v
   B 0v
   C -35.8v

T2 E 0.6V
   B 15.1v
   C -36.5v

R5 671 ohms

D1 checks good

So looks like T1 is bad?
I corrected that above, yes it was just a typo. Voltages are correct for the given transistors.
Had a few other projects to tend to, but finally got around to getting those voltages.

T6 MJF122
E  34.6V
B  35.5v
C  35.1v

T4 TIP29
E  -39.5v
B  -39.2v
C  35.2v
Everything in that string is good. Retested T4 and T3 are good. Replaced T6. Made sure pinouts are all correct. Still showing voltage at the output.