JCM2000 Clean/Reverb Issue?

[IndyWS6]

Greetings
The lead player in my band has a stock JCM2000. During practice the other day, he switched to the clean channel and there was no volume. The only way to get volume out of the clean channel was to dial-up the reverb (e.g. - the reverb level seems to be acting like a clean channel volume pot). The other channel appears to be unaffected. I'm not familiar with these amps, so what should I tell him to look at? If it makes a difference, he does not have a footswitch connected to the head and switches channels at the amp.

Thanks in advance

 

[MississippiMetal]

First thing to do would be to establish whether or not it happens when the footswitch is used to switch the channels.

 

[IndyWS6]

First thing to do would be to establish whether or not it happens when the footswitch is used to switch the channels.

I don't think he has one. Does it use a 1/4" TS cable type FS? Also, it was working properly (clean channel had volume...) and then, it didn't...

Thanks

 

[MississippiMetal]

No it uses a TRS. Is the tone normal when you get the volume up to par through the reverb, or does it sound weird?

 

[IndyWS6]

No it uses a TRS. Is the tone normal when you get the volume up to par through the reverb, or does it sound weird?

It sounds normal to me...

 

[MississippiMetal]

And the reverb sounds normal?

Can Reverb be heard on the red channel? No loss of gain there?

This is a rather unusual issue. I would first check to make sure the reverb cables are seated firmly in the jacks. Next I would check to see if Con 6 on the main board is firmly connected with Con 3 on the pot board.

It sounds like your main signal path has been broken at some point and the signal is getting shunted through the reverb. I'm examining the schematics and I'm suspicious of LDR 3.

Just for shits and giggles, swap the preamp tubes around. Just to say it has been done. This would sound like a tube issue to me if it weren't for the reverb-as-a-volume-control part.

Report back with results.

 

[IndyWS6]

And the reverb sounds normal?

Can Reverb be heard on the red channel? No loss of gain there?

This is a rather unusual issue. I would first check to make sure the reverb cables are seated firmly in the jacks. Next I would check to see if Con 6 on the main board is firmly connected with Con 3 on the pot board.

It sounds like your main signal path has been broken at some point and the signal is getting shunted through the reverb. I'm examining the schematics and I'm suspicious of LDR 3.

I want to say "yes", but I don't remember specifically testing reverb functions on the other channel. We practice again on Thursday, so I can take a closer look. I can also double-check to be certain that the connectors you mentioned are seated firmly.

Thanks again - the responses are much appreciated

 

[MississippiMetal]

And the reverb sounds normal?

Can Reverb be heard on the red channel? No loss of gain there?

This is a rather unusual issue. I would first check to make sure the reverb cables are seated firmly in the jacks. Next I would check to see if Con 6 on the main board is firmly connected with Con 3 on the pot board.

It sounds like your main signal path has been broken at some point and the signal is getting shunted through the reverb. I'm examining the schematics and I'm suspicious of LDR 3.

I want to say "yes", but I don't remember specifically testing reverb functions on the other channel. We practice again on Thursday, so I can take a closer look. I can also double-check to be certain that the connectors you mentioned are seated firmly.

Thanks again - the responses are much appreciated

Check my previous reply. I edited to include a few extra bits of info. Problems with the LDR typically manifest in hum/noise or gain abnormalities, but that's with LDR's that have fallen out of spec. I can see where an LDR that failed completely might cause this issue.

 

[IndyWS6]

And the reverb sounds normal?

Can Reverb be heard on the red channel? No loss of gain there?

This is a rather unusual issue. I would first check to make sure the reverb cables are seated firmly in the jacks. Next I would check to see if Con 6 on the main board is firmly connected with Con 3 on the pot board.

It sounds like your main signal path has been broken at some point and the signal is getting shunted through the reverb. I'm examining the schematics and I'm suspicious of LDR 3.

I want to say "yes", but I don't remember specifically testing reverb functions on the other channel. We practice again on Thursday, so I can take a closer look. I can also double-check to be certain that the connectors you mentioned are seated firmly.

Thanks again - the responses are much appreciated

Check my previous reply. I edited to include a few extra bits of info. Problems with the LDR typically manifest in hum/noise or gain abnormalities, but that's with LDR's that have fallen out of spec. I can see where an LDR that failed completely might cause this issue.

What's an "LDR" (I'm a noob )

 

[MississippiMetal]

And the reverb sounds normal?

Can Reverb be heard on the red channel? No loss of gain there?

This is a rather unusual issue. I would first check to make sure the reverb cables are seated firmly in the jacks. Next I would check to see if Con 6 on the main board is firmly connected with Con 3 on the pot board.

It sounds like your main signal path has been broken at some point and the signal is getting shunted through the reverb. I'm examining the schematics and I'm suspicious of LDR 3.

I want to say "yes", but I don't remember specifically testing reverb functions on the other channel. We practice again on Thursday, so I can take a closer look. I can also double-check to be certain that the connectors you mentioned are seated firmly.

Thanks again - the responses are much appreciated

Check my previous reply. I edited to include a few extra bits of info. Problems with the LDR typically manifest in hum/noise or gain abnormalities, but that's with LDR's that have fallen out of spec. I can see where an LDR that failed completely might cause this issue.

What's an "LDR" (I'm a noob )

Light Dependant Resistor. In the JCM2000's they are used in the channel switching circuit. If It were my amp I'd test the LDR with an ohm meter with the amp powered on while I switched channels to see if the resistance was going low and high like it's supposed to, but I'd rather not encourage you to fiddle around in a guitar amp if you're a self professed n00b.

Try swapping the preamp tubes just to say you've done it, along with reseating the cables coming from the reverb tank into the chassis (both with the amp powered off, of course). If that fails to fix your issue, it's time to let a tech look at it.

 

[IndyWS6]

And the reverb sounds normal?

Can Reverb be heard on the red channel? No loss of gain there?

This is a rather unusual issue. I would first check to make sure the reverb cables are seated firmly in the jacks. Next I would check to see if Con 6 on the main board is firmly connected with Con 3 on the pot board.

It sounds like your main signal path has been broken at some point and the signal is getting shunted through the reverb. I'm examining the schematics and I'm suspicious of LDR 3.

I want to say "yes", but I don't remember specifically testing reverb functions on the other channel. We practice again on Thursday, so I can take a closer look. I can also double-check to be certain that the connectors you mentioned are seated firmly.

Thanks again - the responses are much appreciated

Check my previous reply. I edited to include a few extra bits of info. Problems with the LDR typically manifest in hum/noise or gain abnormalities, but that's with LDR's that have fallen out of spec. I can see where an LDR that failed completely might cause this issue.

What's an "LDR" (I'm a noob )

Light Dependant Resistor. In the JCM2000's they are used in the channel switching circuit. If It were my amp I'd test the LDR with an ohm meter with the amp powered on while I switched channels to see if the resistance was going low and high like it's supposed to, but I'd rather not encourage you to fiddle around in a guitar amp if you're a self professed n00b.

Try swapping the preamp tubes just to say you've done it, along with reseating the cables coming from the reverb tank into the chassis (both with the amp powered off, of course). If that fails to fix your issue, it's time to let a tech look at it.

Thank you, sir