Menu

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

Topics - EddieH

#1
The Newcomer's Forum / Marshall ValveState VS232 repair
January 21, 2021, 10:34:52 AM
Hello and thanks for letting me on the board.   I am starting to re-learn electronics after 20+ years.   Built a couple of guitar pedal kits recently. 

I acquired a Marshall Valvestate VS232 to learn how to repair with.   It was producing a loud hum when I first plugged it in.

It appears someone else had been inside the amp.   
C1 on the poweramp / power supply board was missing.  I went ahead and replaced both c1 / c2 with new caps.
R10 and R18 (same function left vs right channel) were both burnt on the power amp board they were both replaced.    R38 on the main board was burnt also.  It was replaced.
I did re-solder a few of the electrolytic capacitors that appeared to have cold solder joints.

Initial fixes seem to fix right channel and R10 is holding.  There is a very little hum on the right channel now.

I have also tried unplugging the conn cable between the 2 circuit boards.

R38 on the main board will not burn up on the main board with the conn cable unplugged.   
Leads me to believe something is off on the VE- side or the VE+ side that the conn cable provides to the main board.  Looks like from the schematic that R38 is the first resistor on the main board that VE- hits.

R10 continues to burn up regardless and has a strong hum on the left channel. 


Schematic for the power supply / poweramp circuit board

https://drtube.com/schematics/marshall/v230-61-02.pdf

Schematic for the main board.

https://drtube.com/schematics/marshall/v230-60-02.pdf


With the conn cable unplugged I am thinking the problem is still on the power supply / power amp circuit board.   Possible the IC2?

Looking for any other ideas on where to check?

Thanks

Ed