Help diagnosing Fender Princeton Chorus (red knob)

[DaydreamNation]

Hey there! Happy to have found this place. Did a search and didn't seen anything about this exact issue but apologies if I missed something...

I am very green when it comes to electronics repair and need some help diagnosing an issue with my old Fender Princeton Chorus (the red knob 80s/90s non-DSP version). It's been sitting around for quite awhile with this issue: the sound cuts out quite frequently. A hearty thump to the top of the amplifier can make the sound come back in but then it inevitably cuts out again at some point. And when I say "cuts out" I mean nothing, no sound at all except for a slight hiss. It sounds pretty normal when it "cuts in" though, besides some surface noise that's probably mostly related to sitting around for basically a decade.

The amp is all stock as far as I know, apart from the fact that I replaced the 3-prong plug bc the ground broke off. I am confident it's not the speakers or speaker wire, as this issue also happens with headphones (plus I've connected these speakers to a different head with no issues, albeit using different wires/connectors).

Here are some pictures:





I think the issue may be somewhere in this area:



I say that because, when poking around with some wooden chopsticks, it seemed this was the area where lightly tapping stuff could cause the amp to cut back in or out haha. Like I said, very green!

Thanks in advance for any assistance! I'm generally interested in learning more about electronics and circuits but also would love to get this functioning again if it's an easy fix--but not overly attached if it isn't.

Last thing: I'm still learning to read schematics but also would appreciate confirmation that this one I found online appears to be the correct one:

[phatt]

Hi daydream,
Ok, look at the right hand side of Schematic, note how you have 5 sockets.
These are switching sockets, meaning when you insert a plug it also switches the signal path.
Know this; FX loops and like are a nightmare, just waiting to go intermittent.
I personally hate them       

Spray the hole with De-oxit then plug a lead in and out 10 times. If that does not help then the switching tabs inside might be dead.
Now rather than trying to replace them it's far simpler and cost effective to simply take a short lead and bridge the send/return which bypasses the switch.

I have done this simple fix many times with failing FX lopp setups.

If it's the internal switching in the head phone, well that is harder to fix.
You would need to work out a bypass or replace the socket.
Hope it helps.
Phil.

[DaydreamNation]

Hi daydream,
Ok, look at the right hand side of Schematic, note how you have 5 sockets.
These are switching sockets, meaning when you insert a plug it also switches the signal path.
Know this; FX loops and like are a nightmare, just waiting to go intermittent.
I personally hate them       

Spray the hole with De-oxit then plug a lead in and out 10 times. If that does not help then the switching tabs inside might be dead.
Now rather than trying to replace them it's far simpler and cost effective to simply take a short lead and bridge the send/return which bypasses the switch.

I have done this simple fix many times with failing FX lopp setups.

If it's the internal switching in the head phone, well that is harder to fix.
You would need to work out a bypass or replace the socket.
Hope it helps.
Phil.

thanks Phil!! oh DUH of course it makes sense that it's a switching issue, it even makes a sound like when you step on the switch on a cheap stomp box when it cuts out. so yeah I tried the bridge the effects loop trick and it seems much better just scratchy. I'll spray the *s!!t* out of em and see whether it cuts out again after I play for a more extended period—hopefully the headphone jack is fine and it's not multiple things but we'll see. Really appreciate it!