Marshall DSL 40

[Rockranger]

Hey folks,
     Could anyone help me follow the guitar signal in this amp from pin 8 V3 (cathode follower) to the grid of V4. I have a signal on the scope up to R145 and no signal on V4 when a no sound problem occurs (it’s intermittent). I am lost on where the signal goes after R145, any help with signal path would be great!

https://www.diyaudio.com/community/threads/marshall-dsl40cr-farting.331307/

https://www.dropbox.com/s/kktqqcjb0uh3j12/DSL100M2-60-02-V5%20Page1.pdf?dl=0

https://www.dropbox.com/s/puwh2w58a5xpyz9/DSL100M2-60-02-V5%20Page2.pdf?dl=0

https://www.dropbox.com/s/agl2pjclxlne70t/DSL100M2-61-02-V4.pdf?dl=0

[sluckey]

The signal at "Loop In" probably goes to a FX loop. Look for the loop schematic since it's not on the pics you posted. FX loop jacks are a good place to cause intermittent problems. Insert a plug several times into both jacks or maybe put a patch cord between the in and out jacks. Any joy?

[SILVERGUN]

I was lucky. I was taught to read schematics  by a very patient person. The trick is to print out large copies of them and trace the small sections of circuits out with a highlighter.
When dealing with different pages this is extremely helpful and I don't know if there's any better way to do it.

[Rockranger]

Thanks guys no luck playing with the fx loop slucky. Looks like the signal goes to the dfx1 board and so does the loop. With signal generator at 1200hz and volumes at 12 when the amp is working I have 54 VAC leaving pin 8 V3 and only 6.5 VAC entering V4!

[Rockranger]

Owner says he thinks the problem started happening after he plugged his footswitch into the 4ohm speaker jack by accident (JS210). What problems could this cause? When I loose the signal, with the scope on the output the signal comes back when I switch the amp to standby and the wave slowly drops as everything drains out!