R2 not working on Mark III green stripe

[iwkil]

Hi,
I have a Mark III with a problem. Pulling out the dial that activates Rhythm 2 has no effect also footswitching between Rhythm 1 and Rhythm 2 has no effect. Lead channel is perfect and also clean is perfect. I have changed all of the pre amp valves just in case.

Has anyone seen this issue before?

Any help is appreciated.

Thanks
Rob

 

[Boogie Woogie Man]

Check the pre-amp tubes, it's most likely where the problem lies.

 

[iwkil]

Ive changed all of them but no luck, i was wondering if it was possibly the relay that switches between the R1 and R2 channel?

Thanks for your suggestion though.

 

[igfraso]

Check the pre-amp tubes, it's most likely where the problem lies.

R2 and R1 share the same preamp tubes. If R1 sounds normally, then it is not a problem of preamp tubes.
Regards

 

[Boogiebabies]

1. Look for 6V DC at the purple wire to ground near the relay. If 6V's, the DC supply is good.
2. Listen to the relay and if it clicks open and closed. Could be a bad relay.
3. LDR #3 is the volume shunt for R2. If it's bad, there will be no R2 volume.

 

[robredo_mattila]

Have you done the R2 Volume mod?

R2 Died on my amp once, the solder joint on the inside of the amp had snapped off. I resoldered it back in place and it's worked fine since.

 

[iwkil]

Hi,
R2 Mod had not been done.

robredo_mattila

When you had the R2 issue, what happened when you tried to engage R2? on mine I just get the R1 channel ie no sound difference/change.

Thanks Rob.

 

[robredo_mattila]

Hi,
R2 Mod had not been done.

robredo_mattila

When you had the R2 issue, what happened when you tried to engage R2? on mine I just get the R1 channel ie no sound difference/change.

Thanks Rob.

It was just dead. R1 worked, Lead channel worked. But no R2 at all.

This happened to me again more recently and I tried EVERYTHING to get it going, turns out the R2 volume on the back (reverb pot) was turned to Zero. It's always worth checking the little things.

 

[iwkil]

Thanks robredo_mattila,

I'm not sure what you mean when you mention

"turns out the R2 volume on the back (reverb pot) was turned to Zero"

Surely the Reverb Pot is for the Reverb level only or am i missing something?

Thanks for your input.

Rob

 

[iwkil]

Thanks robredo_mattila,

Ah, I understand now, your amp had the R2 mod done which created a MV on the rear panel.

I took the amp apart last night and had a good look around, everything looked fine apart from a burnt resistor which still gave back a respectable reading, would anyone have any schematics for a Mark III?


Thanks
Rob

 

[iwkil]

Hi All,
Dropped the Mark III into my amp tech, he found a bad joint between both sides of the PCB around the rhythm circuitry, he sorted that out and I got the R2 Master Vol mod done.

All is perfect with my amp and I couldn't be happier.

Cheers
Rob