JCM900 reverb tank

[marshalltsl]

Hi
I have a JCM900 DR from a friend that reverb don't work. He want replace reverb tank but It seems ok. 30 ohms on input 250 ohms on output. If you move it the springs sound. reverb tank cables are fine. Is there another way to know if this is okay?

 

[jtcnj]

if you shake the amp or the tank and you hear reverb, it is likely something upstream towards the input in the circuit.
Or at least the output side of the tank's transducer is good, and downstream in the circuit.
I dont know if it is ok to switch the leads to momentarily verify the input side transducer and cable.
I would think so, but I'm no expert.
Swapping the tube that drives the reverb could also be easy thing to check (if it is tube reverb).

 

[marshalltsl]

I shake just the reverb tank. No reverb sound. I tryed other preamp tube and I tryed swamp reverb tank cables. I think issue it's on the amp. On IC3 circuit. My friend said It's cheapest buy a reverb pedal.

 

[Ramo]

Hi
I have a JCM900 DR from a friend that reverb don't work. He want replace reverb tank but It seems ok. 30 ohms on input 250 ohms on output. If you move it the springs sound. reverb tank cables are fine. Is there another way to know if this is okay?View attachment 65478

tell your friend to play chug chug and it does not need reverb,

 

[marshalltsl]

tell your friend to play chug chug and it does not need reverb,

Yeah! Don't need reverb but he need a OD pedal in front to play chug chug. He is a punk-rock player.

 

[Ramo]

Yeah! Don't need reverb but he need a OD pedal in front to play chug chug. He is a punk-rock player.

show him how its done and bring him right side of chug

 

[marshalltsl]

show him how its done and bring him right side of chug

I tryed. But he is punk mind. lol

 

[Ramo]

I tryed. But he is punk mind. lol

never give up on your bros' man, you have to be relentless like tele radio lovers here ( you know who you are) lol

 

[Amp Mad Scientist]

I shake just the reverb tank. No reverb sound. I tryed other preamp tube and I tryed swamp reverb tank cables. I think issue it's on the amp. On IC3 circuit. My friend said It's cheapest buy a reverb pedal.

turn up the reverb control.
Turn up the master volume.
Unplug the cables from the reverb tank.
Touch just the tip of the return cable with your finger.
When you touch the tip of the return, you should hear a buzz noise.
If you hear the buzz when you touch the tip, the return is working on the amp.

If you do not hear the buzz when you touch the return tip, the amp return is not working.

 

[Amp Mad Scientist]

Yeah! Don't need reverb but he need a OD pedal in front to play chug chug. He is a punk-rock player.

The footswitch jack for the reverb can go bad.
If the jack is bad it could stop the reverb from working.
Plug a TRS dual footswitch in and try switching the reverb on / off.

 

[Amp Mad Scientist]

I tryed. But he is punk mind. lol

There is 2 other things:
1. The reverb drive / return IC. This is IC 3.
2. The reverb control IC. This is IC 7.
Either one of those can go bad.

Schematic:

https://drtube.com/schematics/marshall/cd0189-iss7-0349.pdf

 

[marshalltsl]

Thanks Amp Mad Scientist. I'll take a look. My friend don't want fix It at least right now. But we can know what happens on the Jcm900 DR.

 

[marshalltsl]

turn up the reverb control.
Turn up the master volume.
Unplug the cables from the reverb tank.
Touch just the tip of the return cable with your finger.
When you touch the tip of the return, you should hear a buzz noise.
If you hear the buzz when you touch the tip, the return is working on the amp.

If you do not hear the buzz when you touch the return tip, the amp return is not working.

If I touch the tip of return cable (black one) I not hear the buzz. If I touch the tip of red cable I hear a radio station. lol
IC3 and IC7 are cold. 33Vcc. Pin 8 & pin4.

 

[marshalltsl]

My friend bought It from an amp tech. He don't remember if the reverb worked. It's a punk without ridges hairstyle, lol.
This Jcm900 DR has more gain than other ones I have tryed. It has D3 &D4 from preamp board replaced I think.

 

[SIx String Chef]

never give up on your bros' man, you have to be relentless like tele radio lovers here ( you know who you are) lol

Heeeyyy! Don't diss the Teles, man! I guarantee that at some point in your life you're bound to get one.... mark my words! We'll get you , my pretty... BWAHAHAHAHAAAA!

 

[Ramo]

Heeeyyy! Don't diss the Teles, man! I guarantee that at some point in your life you're bound to get one.... mark my words! We'll get you , my pretty... BWAHAHAHAHAAAA!

you have more chance of winning the lottery than me buying that thing lol


you remember scene in Braveheart move? where Mel Gibson is laying and they ask him to accept something cant remember what it was, I know it had something to do with Englad vs Scotland thing, and he screams freeeeeeeeeeeedoooooooooommmmm... I'll be like that
neve
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[marshalltsl]

The footswitch jack for the reverb can go bad.
If the jack is bad it could stop the reverb from working.
Plug a TRS dual footswitch in and try switching the reverb on / off.

I tryed a TRS dual led footswitch. It worked properly. But reverb still Ill. No noises. Amp switch his channels fine.

 

[marshalltsl]

There is 2 other things:
1. The reverb drive / return IC. This is IC 3.
2. The reverb control IC. This is IC 7.
Either one of those can go bad.

Schematic:

https://drtube.com/schematics/marshall/cd0189-iss7-0349.pdf

The amp it's not mine. I can't disasembly. Do you think the issue it's on both IC's? Is this issue a comon problem on Jcm 900?

 

[SIx String Chef]

Never say never, my friend... You already like Strats. It's just a matter of time... Resistance is futile!

Cheers!

 

[Amp Mad Scientist]

The amp it's not mine. I can't disasembly. Do you think the issue it's on both IC's? Is this issue a comon problem on Jcm 900?

Try replacing IC 7.
Put a socket on the board.