Marshall AS80R

[6v6heaven]

This lemon is driving me nuts! It plays and sounds great for a while. I like lots of bass on an acoustic, so it thunders it out. BUT it just keeps letting me down, goes silent, no output. I leave it for 5 minutes and its back and plays again for 10-15 minutes. Very random. Had it in the shop, they played music into all day and say they could find no fault. Plug back in my Ovation and a mike and goes dead again in random 5- 10 minutes. Any thoughts/suggestions. Anybody got the schematic?

[vintagekiki]

Marshall AS50R

May be help Marshall AS50R

[doctor]

May be help Marshall AS50R

AS80R schematics:

[6v6heaven]

Thanks Doc. I guess its thermal?

Thanks for the schematics. Lots to work through here. From my posted symptoms I'm assuming its a component heating up. Those TDA 1514A's probably have a thermal shut down which would reset. Anyone know if there are any other likely IC's in here with thermal protection which could be causing the problem? Its so random when it happens but maybe the power supply is cutting out..is that possible? Or any other ideas on what to look for? Thanks 6V6Heaven

[Enzo]

More likely dirty cutout contacts on jacks than thermalling parts.

[6v6heaven]

Thanks

Thanks Enzo. I will give that a more thorough try. I much prefer simple solutions, but sometimes nothing seems to work.

[Ronsonic]

Treat as an intermittent until proven otherwise. I know, it seems thermal, but....

Always start with the looping jacks. Mechanicals more often than electrical faults. Employ percussive diagnostics. Run signal, like 100Hz and shake the thing.

It may be that Marshall neglected the H/S paste or failed to tighten down an IC or ... Mostly, we can expect a self contained product to withstand any reasonable input, even your thunderous dreadnaught.

[6v6heaven]

Thanks I'm going in ..... encouraged

Thanks for the sensible direction. I'm going to bypass all those jack links if I have to...but I will find that gremlin!! Cheers .

[audiomax62]

Thank you a lot for the schematics, I'm just registered in this forum, and I have a friend with EXACTLY the same problem with the AS80R. I was afraid to find a lot of hated electronic switch in the schematics, but I didn't find it (fortunately!!).

I think I'll investigate especially in the footswitch contacts, probably this can be the place where little mechanical problems can cause the intermittency of the sound without too much scratch noise added.

In my experience i'd tend to exclude thermal problems, the schematics is complete or there's something missing?

Thank you again!!

[IxtabStudios]

Hello everyone. I have an AS50R with a bad power transformer. The ratings are not specified on the transformer nor in the schematics (Thanks for the post by the way).

Does anyone know the VA and voltage spec for this thing? The fender reference is TD63089F0.

Cheers.

[6v6heaven]

Solved!

Found the gremlin! It was the left line out jack socket. Had it wired up to the scope to the speakers with 1Khz going in. Fired up both channels looked good for 2 minutes, then one channel just faded away as I watched it. Sharp shocks to tyhe chassis didn't change anything. Started plugging and removing a new jack plug in every jack socket. When I got to the left line out, that signal "grew" back. Used some contact cleaner on the jack plug and gave that a whirl into all the jack sockets. Been running now even with acoustic guitar input for a couple of hours. Sure glad you guys with the knowledge directed me to those jack sockets, or I would have been replacing amp chips by now....THANKS MUCH. Still not sure why a bit of much in there would cause the signal to fade out and back, would have thought it should have been instant. But its clear there a whole bunch to learn for me. Thanks again.

[bobot62]

gud day sir, i am new here, can i ask a copy of the circuit diagram of this marshall as50r amp?

May be help Marshall AS50R

[DrGonz78]

Here it is...

[bobot62]

Here it is...

thank you so much sir for the as50r schematics

[ocito54]

Hello, maybe the same trouble with my amps. Can't open the schematics for my AS80R. Please, can you post them ? Thank you very much.