need troubleshooting advice from anyone with early 80s carvin x-100b experience.

[ALBATROS1234]

a friend brought me a found/abandoned  broken carvin 100 watt head and knew i messed with tubes.took it home to evaluate as one of the 6L6s was shattered.i popped in another 6L6 but it was blowing fuses which was filter cap can shorted to ground. i sprayed deoxit in pots,jacks and sockets. testing found another dead 6L6 and a very weak 12ax7. put 4 good 6L6s and a new 12ax7 then brought it up on the variac and now the lead drive channel functions perfectly as does all controls and graphic eq but when i switch it to rhythm/clean i get no sound. the led is bright on the rhythm channel when its selected but when i select lead drive the lead drive led lights up but the rhythm led only goes dim. this amp if far more complicated than anything i have messed with and seems to use transistor to channel switch. i think i have found a schematic which matches the amp but dont want to just shotgun and change half the components if i can help it. i was wondering if anyone had experience with this amp and knew if this was a problem with them or had an understanding of the switching system. trawling the web seems to indicate this as a problem as a few random threads here and there complain of similar problem. visual inspection i found a cold solder joint at 1 of the transistors but reflowing it did not help. thank you in advance for any replies.

[PRR]

DC voltages.

Signal tracing.

You should know the drill by now.

[ALBATROS1234]

i know.....i guess the parts count has me intimidated and i kinda hoped perhaps someone may have encountered the problem and could give a nudge in the right direction. especially since the sockets are covered over by a massive board so i cant even test pin voltages in real time. and i dont have a footswitch  which if it worked would point to the push pull pot on the lead drive vol which toggles channels. and i dont get the dim led when it seems the channels have switched since i either have sound or no sound. it was a long shot but i figured i would try here as i normally fiddle with super simple 1940s/50s tech amps. which to me sounds so much more pure in tone. to my ears the more simple the circuit the more of the guitars actual tone you hear. its like cars. they used to be simple machines that you used to get from a to b. now theres so many bells and whistles theres so much crap that can fail. just one mans opinion mind you. thank you sir for taking the time to reply i do appreciate it.

[2deaf]

The pins for those tube sockets should be protruding through the massive board so you should be able to test the voltages.  What is the board number?  If the reverb is driven by a 4558 Op Amp, the attached schematic may be closer to what you have.   

[ALBATROS1234]

sorry for the delay in the response i have been busy the last couple days and havent had a chance to look at the beast. first off you are correct, i stupidly had a newbie moment and did not realize there are the solder connections for the pin sockets accesible. i assumed there were normal sockets which were wired to the board out of view so that will allow me to check some stuff.i have mainly worked on stuff i build or really old stuff from the 40s ad 50s and all have had exposed old style sockets and point to point or simple turret type boards. as for board number it says X-100-H on the board. the schematic you attached doesnt seem right as it has a selector for 25%-50% and 100%. the  version i have has 60% or 100% power settings . the schematic i attached is the only one i could find which has the latter mentioned config so thats why i went with it. thank you for your response in a bit i am going to see what i can see now that i realize i can test voltages on tubes. also checking confirms a 4558 powering the reverb

[shooter]

but when i switch it to rhythm/clean i get no sound.

most mechanical things will fail before electronic things

you schematic did show a transistor driving the "suspect" always lit LED, but I believe it was controlled by switching.

the lead drive channel functions perfectly as does all controls and graphic eq

that tells me you're 90% done, but that last 10% is what we get our jolly's from 

[2deaf]

My board is 30-X100-4B, so I don't think I can be of any help.

As PCB's go, this one isn't bad.  At least it is only two-sided and I can clearly see the traces on both sides.

[ALBATROS1234]

thanks gents im just gonna have to pick through it when i have time and replace suspect components until something works.

[DummyLoad]

the schematic attached may be closer to what you have? check the -15V and +15V supply and +5V supplies. use your smart phone as a signal source and with a scope or signal tracer, see if you have signal at the channel switching JFETs - on the OCT 2007 schematic those are Q102 and Q105. if you have clean (RHYTHM) signal up to there, then check for control signal on the gates - if you have the clean channel on, then you should have "0V" at R30 and -15-ish volts at R32.

for signal switching with the JFETs the truth table is 0V=on and -15V=off when applied to the gate.

so for the lead channel active we'd see -15V at gate of Q105 and 0V (or some very small positive V) at the gate of Q102. for the rhythm channel, we'd the reverse, 0V at gate of Q105 and -15V at gate of Q102.   

if you can't find signal at Q105 work back to the input of the rhythm channel: if you don't have signal at pin 5 of A7.B then check V11.A if you have signal at pin 5 of A7.B but not at R23 & R29 node then A7.B is defective , if you have signal at the source of Q105 (also the junction of R23&R29), but no signal at the drain of Q105, then JFET Q105 is bad or the switching logic is not working. 

--pete

[ALBATROS1234]

Thanks that helps. I actually downloaded a signal generator app this weekend and I have a student grade o scope. This amp seems to be around 1983 from what I see wouldn't a 2007 schematic be for the reissue x amps? I will compare when I get home tonight though. Appreciate the help sir