Fender Cyber Twin no master Volume

[dboerst]

I have a couple Cyber twins and one of the the master volumes does not work. Amp powers up fine. Goes thru all boot up procedures. It doesn't move by MIDI. Doesn't effect the output. Power amp section is good as sometimes it will play at full volume. Any ideas?

[Amp Kat]

Try a signal to the return in and see if it works.

[dboerst]

I did and no it did not work. The send does work, without effects, I talked to a couple REPS when I was gigging 2 of them. They asked me what I would like in the second version....didn't use any suggestions so I went and bought a 1992 30th Anniversary Marshall (blue one) and a Line 6 Vetta IIHD. Could it be a EPROM error? sound/hum does emit thought speakers and phones output.

[Amp Kat]

Not sure but I think I worked on one and it had some loose solder connections. Could be a output transistor problem because hum on the outs is one of the direct symptoms and also the return having hum points to that as well. The EEPROM and DSP are in between the preamp and out so it should work as the preamp out.

[dboerst]

When I mentioned hum it was the "normal" sound that emulates from the power amp. When moving the master volume pot there isn't a reading on the LED/crt screen. I realize it isn't a Cathode Ray Tube but just tying to explain the 'main" display. I have a schematic as there any test point I could check? I do have another fully working Cyber Twin to reference from possibly. Thank you for replying!!!

[Amp Kat]

I was hoping Enzo would reply as he helped me fix the one I had done and it is possible that yours has a loose connection or bad solder joint on the master pot. Not sure the voltage checks or test points will help but a good visual inspection may suffice along with a chop stick to poke around with. Of course a signal generator and a scope would be worth it's weight in gold here as you could drop it right on that master pot and see exactly if that signal is there or not. I would do an ohm check on the Xout transistors just for fun.

[dboerst]

Yeh I will check the output MOSFETS/Transistors. It kind of seems one side would work. The 12ax7 heaters do light so there is power possibly close to 300 volts, that is if Fender used the "correct" way of doing the preamp IMO. There isn't any signal coming from the XLR/Cannon outs.