R2 volume mod doesn't work

[bernhard]

hi, i have a problem with my mark III. It's a bluestripe combo non-simulclass (60 Watt) with reverb and eq. Because the volume of R2 is much louder as R1, i had installed the R2 volume mod like the instructions and pictures on this board (R130 snippep out and 250k taper pod between R131 and R130), but it doesn't work. It seems that nothing changed and i can't reduce the loudness of R2 with the pod. Please help.

greetings from munich
bernhard

 

[disassembled]

How about posting a picture of your work?


Greg

 

[edward]

How did you wire the pot ...side and center lugs?

Edward

 

[bernhard]

ok, here are two pics:




the blue wire is soldered to R131 and the green to R130
my mark III has no voltage switch, so i attached the pot at this place.

greetings
Bernhard

 

[Boogiebabies]

Bernhard,

Try Soldering the green wire to the first lug on the left. If that does not work, try grounding the third lug to the back of the pot.

 

[bernhard]

Hi Boogiebabies,

i soldered the green wire to the other lug of the pod, no change, then i grounded the free lug to the back of the pod, respectively to the chassis, no change as well. yet another idea ?

greetings
Bernhard

 

[Buddy]

cold solder joint ?
It happens ...

 

[disassembled]

Have you tested the pot to make sure it works?

Greg

 

[bernhard]

yes, i have measured the pot, it works in a range between 0 and 250 kiloohm.
cold solder joint ? maybe, but i don't understand, why the R2 in this case actually works ?

 

[bernhard]

Hi,

can you tell me, what's this ? It doesn't looks like a work from mesa. Is this another mod ? i haven't seen this on any picture in the forum. The opto coupler is wired to the master and lead-master pot.




can this eventually be the reason for my R2 problem ???

Bernhard

 

[Restless Rocks]

Your R2 pot appears to have been wired correctly in the first place. I would guess the LDR3 is not funtioning which grounds it when R2 is engaged. Also note the other LDR replacement just above R130.

The other LDR "MOD" appears to be a replacement for the lead Master LDR5 which must have failed. Replacing these babies is tricky work even for the experienced tech evidenced by this fellow's choice to retrofit the new one as opposed to trying to remove the old one. I would suggest finding a Mesa Tech or consider sending it to Petaluma for an overhaul. Mike B. would be the best choice.

 

[bernhard]

Which of the LDRs is LDR3 ? one of the stacked ?

By the way, many thanks for helping to all !!!

 

[Restless Rocks]

Yes! Unfortunatly it is the one on the bottom. I refer to them as LDR3a and LDR3b as they both have a funtion for R2. The next step is to get in there with a multimeter and see what's working. Again, probably a job for a tech as the amp must be fired up to test operation of the switching circuit and the LDR's.