marshall jcm 2000 tsl swithching issues

[tonepumpamps]

Hello,

I have a 60 watt Marshall TSL in the shop that is having switching issues. It won't switch from clean to overdrive. The leds light up but the amp goes silent. It doesn't matter if you use the pushbuttons or the footswitch, same result.

I have checked the power supply and all voltages are good. I've also checked Relay 1 and that checks out good. There's a lot going on with the switching and I'm having a little trouble tracing what exactly goes on during the switching proccess.

Any one have any experience with this? Any help would be apprecitated.



TL60-60-02 (2003) iss7.pdf

[soundguruman]

marshall TSL 60W.pdf
I can't open the pdf you posted so I am trying this one...

obviously there is a number of switching functions not clearly labeled on the schematic...
not just the relay
it is challenging to tell which one is working in what mode.

But check the power supply voltages verify that + 15 volt at - 15 volt supplies and both working
and check +24 volt at R128, + 15 at R 85, -15 at R84, check the IC 2C for + - 15 volt
if something goes bad it may load down the power supply voltage, or power supply(s) may not be all functional to start with.

[tonepumpamps]

Thanks for posting the schematic.
I've checked the power supplies and they were good. I'm gonna have to get real cozy with the schematic & try to track down the problem
Up till now Mesa Boogies were my least favorite switching system to work on, this ones got em' beat.

[km6xz]

If the relay 1 is working, and the LED for clean/od is lighting, you have 90% of the channel switching proven to be good. The same source that drives the led drives a dim, an fet (F11) that drops level to the grid of V3. Does the signal reach the plate of V3? If so, focus on RL2 and the connectors CON15 and its other end CON9.
It looks complicated but there are actually few points that are able to cause the specific symptoms, which means a few logical test points of the circuit isolates the area that is not working.

[tonepumpamps]

Problem solved! (hopefully) After getting cozy and spending some quality time with the schematic I finally deciphered what Marshall has going on with the signal flow and channel switching.
The problem is the 2 P-channel Jfets, F8 and F9 on the schematic. I wasn't getting any signal to the grid of V2, figuring out that the jfet holds the grid at ground until switched, I removed the jfet and I got my signal on the grid. Traced the signal a little more and found out F9 was also bad.
After I figured it out it seemed simple. It's nice when my brain finally decides to cooperated & I get something figured out