JCM2000TSL - Send/Return Problem

[LucaMetalMyLife]

Hi all, I recently bought a Marshall JCM 2000 TSL, it sounds awesome, but when I plug any pedal through the FX loop the volume suddenly drops.
If I hit the top of the head with my hand, the problem solves temporarily , but after 1 or 2 minutes of playing the volume drops another time.
I am an engineer and I know how my head works, but I can't understand why there is this issue.
I have tried a lot of pedals like Chorus, Reverb and Delay but the problem persists.
If I plug directly the send with the return of the amplifier with a patch cable the problem occurs.

What can I do?
I have tried to replace some diodes in the FX loop circuit, I have tested all the trimmers in the board and they work fine.
I can't find a solution or even understand where the problem is.

Thank you!

Keep rockin' with <3

 

[scozz]

I’m not too familiar with your amp, but some Marshalls do loose a bit of volume when the loop is engaged.

This occurs mostly at low volumes, and as you turn the amp louder and louder the discrepancy goes away.

Although I don’t recall anyone referring to their Tsl as having this situation.

Others will be along to give a better diagnosis than I can.

Btw, to The Marshall Forum.

 

[anitoli]

Does the amp have a line level switch? Usually they are -10 and +4 db. have you tried switching it in out?

 

[The Dose of Harmony]

Tsl’s have a drop in volume on the Fx loop , its one of the very well know issues of Tsl’s you should put a eq or sone kind of booster to compensate .

what year its your head?

 

[Mitchell Pearrow]

Hi all, I recently bought a Marshall JCM 2000 TSL, it sounds awesome, but when I plug any pedal through the FX loop the volume suddenly drops.
If I hit the top of the head with my hand, the problem solves temporarily , but after 1 or 2 minutes of playing the volume drops another time.
I am an engineer and I know how my head works, but I can't understand why there is this issue.
I have tried a lot of pedals like Chorus, Reverb and Delay but the problem persists.
If I plug directly the send with the return of the amplifier with a patch cable the problem occurs.

What can I do?
I have tried to replace some diodes in the FX loop circuit, I have tested all the trimmers in the board and they work fine.
I can't find a solution or even understand where the problem is.

Thank you!

Keep rockin' with <3

To the forum
Hope there is nothing really wrong with your amp, I have no first hand experience with your amp brother.
Cheers
Mitch

 

[Georgiatec]

Have you tried cleaning the sockets with deoxit or similar?

 

[Jethro Rocker]

I just turn my amp up a touch as I always use loop. It shouldnt however get louder amd quieter as youhit the top. Have you tried changing pre amp tubes? Could well be that too

 

[CraigerSS]

Could be dirty F/X loop connector contacts, this can be a common problem with f/x loops.
Try cleaning the loop connector contacts, check for cold solder joints or replace them.
Plug a patch cable in to the loop and wiggle the plugs to see if fixes it or makes it worse.
Also, on my DSL50 the -10/+4db switch can be finicky, clean those contacts too.

 

[SkyMonkey]

Dirty FX Mix pot?
Deoxit and retest.

 

[GT08]

Clean the sockets....check socket contacts.

How do the level push buttons effect it?

Does it occur on both loops?

Rock n' roll

 

[LucaMetalMyLife]

I’m not too familiar with your amp, but some Marshalls do loose a bit of volume when the loop is engaged.

This occurs mostly at low volumes, and as you turn the amp louder and louder the discrepancy goes away.

Although I don’t recall anyone referring to their Tsl as having this situation.

Others will be along to give a better diagnosis than I can.

Btw, to The Marshall Forum.

Yes, I mean....it drops the 90% of the volume and the bass are cutted.

 

[LucaMetalMyLife]

Clean the sockets....check socket contacts.

How do the level push buttons effect it?

Does it occur on both loops?

Rock n' roll

Hi, what push buttons do you mean? The FxLoopA and FxLoopB?
They don't affect the volume, I can't understand how they work.

Thanks

 

[LucaMetalMyLife]

Dirty FX Mix pot?
Deoxit and retest.

Ok, I am going to replace it...
Thanks

 

[LucaMetalMyLife]

Could be dirty F/X loop connector contacts, this can be a common problem with f/x loops.
Try cleaning the loop connector contacts, check for cold solder joints or replace them.
Plug a patch cable in to the loop and wiggle the plugs to see if fixes it or makes it worse.
Also, on my DSL50 the -10/+4db switch can be finicky, clean those contacts too.

I will try that.

Thank you

 

[LucaMetalMyLife]

I just turn my amp up a touch as I always use loop. It shouldnt however get louder amd quieter as youhit the top. Have you tried changing pre amp tubes? Could well be that too

I don't think so.
I mean, when I don't use the fx loop the problem never occours...

 

[LucaMetalMyLife]

Does the amp have a line level switch? Usually they are -10 and +4 db. have you tried switching it in out?

Hi, I tried to push in and out the loop level A and loop level B in all combinations you can set...
Nothing changes.

 

[Georgiatec]

I don't think so.
I mean, when I don't use the fx loop the problem never occours...

This would point to dirty contacts in the jack sockets. My old JCM2000 DSL100 would suffer the same fault occasionally. Drop in volume and fidelity of signal is almost always a dodgy connection.

 

[GT08]

Download and print the manual.....it's free.

Rock n' roll

 

[SkyMonkey]

Ok, I am going to replace it...

Probably no need to replace the FX Mix pot.
Just try cleaning it with a squirt of Deoxit.
It would probably mean pulling the chassis to get to it (so clean all the others at the same time).
It's a long shot, but could be the problem.

 

[scozz]

Yes, I mean....it drops the 90% of the volume and the bass are cutted.

Oh, no, ok, I’m talking just a couple of dbs, not anything near 90%!


Definitely an issue, that goes without saying.