Mesa mark III blue stripes good schematic!

[Reeko81]

Hi Boogiers! This is my first post here...i'm a happy owner of a mesa mark III blue stripes...i've had problem with the R2 volume mod and now my amp is checked by a technician...but the problem is that he need a better schematic, cause the one available here on the web is not good...has anyone got a better one?
Maybe there is a circuit interuption because my new volume pot seems to control the first master volume!!!!!!
Riccardo

 

[Boogiebabies]

Call Mesa or get a more competent amp tech. The schematic for the MK III is pretty close. The R2 relays in to the circuit at the the same spot that the lead channel does. All the Pull R2 relay does is add more gain via the V2A cathode cap and resistor. Your Volume 1 Should only drive the V1 and the amps total input. If you have another pot for an R2 Master is causing a resisting property instead of a taper or bypass property this would lower the gain to the rest of the preamp circuit unless it was done correctly. If you are lowering the gain to the V2 A, all the gain from the V1 A&B is reduced and cannot be sent to the V3 A&B and then the PI.

How does it effect the lead drive? Probably not at all since this is a different part of the circuit. It connects similarly to the V2A, but is switched in with seperate LDR's.


Good Luck.

 

[Reeko81]

Call Mesa or get a more competent amp tech. The schematic for the MK III is pretty close. The R2 relays in to the circuit at the the same spot that the lead channel does. All the Pull R2 relay does is add more gain via the V2A cathode cap and resistor. Your Volume 1 Should only drive the V1 and the amps total input. If you have another pot for an R2 Master is causing a resisting property instead of a taper or bypass property this would lower the gain to the rest of the preamp circuit unless it was done correctly. If you are lowering the gain to the V2 A, all the gain from the V1 A&B is reduced and cannot be sent to the V3 A&B and then the PI.
Good Luck.

How does it effect the lead drive? Probably not at all since this is a different part of the circuit. It connects similarly to the V2A, but is switched in with seperate LDR's.
Thanks for the quick answer!
Well i believe that i've made my great error using a bad iron to solder all the cable for the mod...infact i used a lot of heat to solder and i've made some interruption to the board...infact now it is like there is an interruption on the circuit (as i told before).
Now the r2 volume pot act as a master volume for all the channel...!!!!
Since i swapped out the r130 resistor my r2 channel is now boosted and the volume pot doesn't affect on it because it become like a new master volume...
When i did the mod it works only for 10 minutes, then my amp started buzzing and stopped ...
I believe that now the best solution is to unsolder the board and check it at the bottom, but my tecnician hasn't done it yet!
I believe that is not a hard repair, but the problem is that mesa gave me also the same bad schematic avalaible on the web, and with this one it's difficult to do a good repair...does anyone so a good copy of this schematic?
Riccardo

 

[Boogiebabies]

It is the best I know of. If you have a broken solder pad or trace, they are easy to fix with a jumper. If it is a bad pad, you will have to solder a lead to the trace and jump it to the cap or resistor.

Good Luck.

 

[Reeko81]

It is the best I know of. If you have a broken solder pad or trace, they are easy to fix with a jumper. If it is a bad pad, you will have to solder a lead to the trace and jump it to the cap or resistor.

Good Luck.

You've been helpful, but i want to ask you more...do you know what really does this volume pot in that point of the circuit?And why i have to connect a wire to r131 and one tho the hole of the removed r130?
What really affect these resistors in the circuit board ?
I tell you because in the schematic there is no trace of a number to identify the r130 and r131 resistors so if you know more you can help me much more than you believe!
Riccardo

 

[Boogiebabies]

There is no reference because the MK III was an identical copy of the MK IIC+ circuit. The only thing is that they are on different circuit boards. The IIC+ was an a old style, easy to work on type board where the MK III is on a current generation type of PCB. Thin traces, marks and lettering for caps and resistors and relays. The artwork is what is different.
The R2 trips the relay to revoice the V2A into a higher gain stage to give the second channel more gain. Any type of pot would be there to increase or decrease the amount of gain (Volume as well) to the next preamp stage to be amplified throughout the rest of the preamp and help even it out with the output of the clean, R2 and lead stages. I would start all over again and use jumpers instead.