Marshall AS50R Cutting Out

[dpm309]

I am working on my friend's Marshall AS50R acoustic guitar amp that is experiencing intermittent cutting out. I worked on one of these several years ago and solved the problem by cleaning the effects loop jacks. Tried it on this one several times with no luck. Trying to find a schematic and am having trouble accessing Music Electronics Forum. Doing a google search shows a few hits with service manual and schematic for the AS50R but am getting message " Problem loading page". Got the same error trying to access their Forum. Are they still in existence? Does anyone know where I can get the schematic?Thanks, Dan

[dpm309]

I finally found a schematic and have attached it here. Where should I begin trying to find the cause of the amp cutting out. I also tried jumpering the effects loop with no luck.

[dpm309]

Looks like Music Electronics Forum is down. Read a few posts about the passing of Enzo who was behind MEF. Will pull the chassis on look for bad solder joints etc.

[shooter]

experiencing intermittent cutting out.

 
looking at 7 pages of schematics I can find a near infinite amount of places that could happen and didn't see waldo either 


how often, every song, once a set, twice a week??


a meter, scope, a sig-gen and time will be your friend, assuming there is no obvious visuals or burnt fingers on hot ICS or transistors. 
the biggest problem is the number of "variables" like, footswitches on/off, eq on off, CH1, CH2..........


look up the data sheet on the PA "chip"  most have a thermal protection, voltage protection, etal, it might be "tripping" on a fault circuit

[dpm309]

The cutting out is very random. Sometimes it can go for an hour or so with no issues, other times it happens right away. Plugged it in just now and it was acting up immediately. Cleaned the loop jacks (for the 3rd time today) and is not cutting yet. Going to have to play it awhile to see if I can get it to cut out again. I might also pull the chassis and give the jacks a good cleaning. Never liked Cliff jacks and am thinking they may be the problem. Will post again after I run this for a couple of days.

[mresistor]

I absolutely dislike Cliff jacks and will use Switchcraft almost always.

[dpm309]

I always use Switchcraft or Nuetrix jacks in all of my amp and effects pedals builds. Pulled the chassis and did a thorough cleaning of the jacks. Been running it for a few days with no issues.

[scstill]

I absolutely dislike Cliff jacks and will use Switchcraft almost always.

I have a build that I'm going get back to soon.
https://stillampd.com/supro-1696tn-repro

First time using cliff...
I have replaced all the switchcraft with cliff
to isolate the jacks from the chassis to eliminate potential ground loops.
Hoping I'm not going to be in trouble. Haven't wired yet so could switch back.
four input cliffs and one footswitch
Doesn't Marshall always use cliffs

[dpm309]

Yes, Marshall usually always uses cliff jacks. You can buy isolating washers for Switchcraft jacks. I have used them and they do work just fine.