JCM2000TSL - Send/Return Problem

[LucaMetalMyLife]

Hi Guys.
I disassembled all the head.
I tested all single contact on the board.
I found 2 problems:
If you remove the grid behind the head you find 3 pins below preamp tubes.
That pins aren't connected to anything.... is it a problem? The connector name is CON2.
The other problem is a flat connector (CON 14) that has some contact problem with the pins on the board.
I think I'm going to replace it with a new one.

What do you think?

Thanks so much.
I appreciate your awesome suggestions.

 

[Georgiatec]

Hi Guys.
I disassembled all the head.
I tested all single contact on the board.
I found 2 problems:
If you remove the grid behind the head you find 3 pins below preamp tubes.
That pins aren't connected to anything.... is it a problem? The connector name is CON2.
The other problem is a flat connector (CON 14) that has some contact problem with the pins on the board.
I think I'm going to replace it with a new one.

What do you think?

Thanks so much.
I appreciate your awesome suggestions.

Do not remove or replace the three pin CON ports....they are test points. The externel CON 2 is the bias test point.
It seems to me if you do not know what these are and what they are for you should just take your amp to a tech, as your lack of knowledge could either damage your amp or give you a lethal shock.

 

[StuckInDeAttica]

My best troubleshooting tool for tube amps with intermittent issues affected by shock or temperature has been my plastic chop sticks. I go around tapping on or around all components and see if anything changes. Something I learned from Mr Kendrick and found it to be very useful. I am also an electrical engineer and want to find root cause by measuring and analyzing everything, but I also like to find the problem quickly and don't like high voltage jolts. Good Luck!

 

[Lt.Dan]

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.

I had a JTM60 that was the same way, so I never used the FX loop. But then again I only used a few effects pedals. I always choose one's that had a true bypass.
But hitting the top of the amp to make it better tells me something is wrong.

 

[The Dose of Harmony]

Hi Guys.
I disassembled all the head.
I tested all single contact on the board.
I found 2 problems:
If you remove the grid behind the head you find 3 pins below preamp tubes.
That pins aren't connected to anything.... is it a problem? The connector name is CON2.
The other problem is a flat connector (CON 14) that has some contact problem with the pins on the board.
I think I'm going to replace it with a new one.

What do you think?

Thanks so much.
I appreciate your awesome suggestions.

Dude Sorry !

but if dont even know what are those pins for you are lost!

You are gonna fuck up your amp!

Take your amp to a tech !
Listen to Georgiatec!

 

[mfratus2001]

Many controls and connectors I run across have been gunked up by a contact cleaner that I have not identified for certain. Some times it requires replacement of the control or at least severe cleaning with a dangerous cleaner. Sometimes even that does not work. I suspect that it is a highly hyped and advertised brand. I use a silicone-based contact cleaner, MG Chemicals 404B.
You did not say if the loop level switch had an effect, but it could be dirty or gunked up.
The fact that hitting it clears it up proves that the problem is mechanical, not electrical. You don't need to change any electrical components unless they are physically broken.

 

[Vesperado]

This topic has been discussed in a few threads already. You will find more about it utilizing the search feature. Good luck.

 

[GT08]

You require.........FAST EVAPORATING ELCTRICAL/CONTACT CLEANER. This will not "gunk up" anything.

Rock n' roll

 

[neoclassical]

Clean the contacts, but also make sure the fx loop level pot is maxed. THere is also a mod that can be done, but I run a rack effect unit in my loop.

 

[lespaulr0cker]

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

Most of the 1/4” jacks on the TSL have some additional contacts that switch on/off when the plug is inserted/removed. These are separate contact points from the actual jack plug contacts. These contacts will sometimes become tarnished and an increase in resistance will occur. You may want to insure these are clean and making good contact.

 

[The Dose of Harmony]

Most of the 1/4” jacks on the TSL have some additional contacts that switch on/off when the plug is inserted/removed. These are separate contact points from the actual jack plug contacts. These contacts will sometimes become tarnished and an increase in resistance will occur. You may want to insure these are clean and making good contact.

Yes sir there is a well documented video on you tube and at the end he talks about the common problems and does a repair on those Jacks!
I will posted soon but i think might be already posted on this foroum!

 

[LucaMetalMyLife]

Hi everyone!
I finally solved the problem!

There is a little transistor that drives a relè which selects if the signal has to pass through the send/return or through the dry circuit.

This relè needs 24v in order to trigger.
The tension that the transistor provided before the fix was about 16v so the relè was is a undefined state.

By replacing the transistor the relè now is driven with 22.5v (very close to 24v).

Now there is no more the undefined state so when i plug the return male jack, the transistor provides the correct tension to the relè.

Thank you guys!
Byeeee!

Luca

 

[Rick407PAS]

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

im right there with you, once I engage the loop, or send and return, I get nothing, aside from that, all good. i haven’t a clue

 

[Rick407PAS]

Hi everyone!
I finally solved the problem!

There is a little transistor that drives a relè which selects if the signal has to pass through the send/return or through the dry circuit.

This relè needs 24v in order to trigger.
The tension that the transistor provided before the fix was about 16v so the relè was is a undefined state.

By replacing the transistor the relè now is driven with 22.5v (very close to 24v).

Now there is no more the undefined state so when i plug the return male jack, the transistor provides the correct tension to the relè.

Thank you guys!
Byeeee!

Luca

if you could pass on the name of the transister, that might help me get through this nightmare.
Thanks Luca
Rick

 

[Rick407PAS]

than

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.

ks

 

[Rick407PAS]

than

ks

I fixed it, or, I was doing it wrong, most likely, all good.
Thanks everyone :