Marshall 1987x woes.. STILL!

[jezzzz2003]

Some of you may remember my earlier thread on this issue,

My reissue head is acting up intermittently, it seems to be connected with the FX loop because the problem only occurs when its engaged.

The amp will be loud and the volumes will both be full up no matter where theyre set, I tap the amp hard and it will dissapear, then re-appear intermittently,
Ive tried resoldering most things on the small PCB and couldnt see anything obdvious that could be causing the fault, I even resoldered the wires that go to the inputs [red and black] but to no avail,
any ideas on what this could be?
thanks.

[gtrnstuff]

Don't know if this would shed any light. Have you tried a jumper across the loop? Just a patch cable from out to in.

[jezzzz2003]

Don't know if this would shed any light. Have you tried a jumper across the loop? Just a patch cable from out to in.

Yes, but that would usually yield the opposite result, such as low output to normal with them bridged.

[John Phillips]

If jumpering the jacks cures it, it sounds like it's a switch contact problem in the jacks. There's actually no real reason to use it like that - if you don't want to use the loop, fully bypass it with the switch. If you do want to use it, the signal is going through the effects rather than the switch contacts anyway.

If it's that it still cuts out when the loop is actually in use as well, it could be an IC problem. It's rare, but I have come across more than one IC with a vibration-induced internal fault that does things like that.

[jezzzz2003]

If jumpering the jacks cures it, it sounds like it's a switch contact problem in the jacks. There's actually no real reason to use it like that - if you don't want to use the loop, fully bypass it with the switch. If you do want to use it, the signal is going through the effects rather than the switch contacts anyway.

If it's that it still cuts out when the loop is actually in use as well, it could be an IC problem. It's rare, but I have come across more than one IC with a vibration-induced internal fault that does things like that.

Thanks John,

I havent tried simply jupering the send and return jacks as yet but do use the loop for time based FX all the time, should I try changing the IC in that case?
thanks again.

[John Phillips]

Yes, if it's cutting out with effects in the the loop, it's not the switch contacts. It could possibly be the level switch, but beyond that it has to be a solder joint or component problem. Resistors can have internal cracks too, although it's much less common with modern types than old carbon-comps.

I would change the IC first.

[jezzzz2003]

UPDATE/

Our tech had a look at the loop over the weekend and resoldered all connections and did some trouble shooting, the amp is slightly improved, there is now no noise when the loop is engaged, there used to be some static noise and interferance whenever I used it, the main problem of the volume jumps are still there though, now it doesnt matter wheather or not the loop is being used so were going to go over it again tomorrow, he says it sounds like a grounding issue if the volume is jumping intermittently, hopefully we can find it because Im so sick of my amp being like this
!:BITCH

[jezzzz2003]

Problem solved, yay!
My Old Man sorted it out, found a dry joint on the track between R-9 and PK-2, its all good now,
thanks guys.