SOLVED Thermionic Deluxe - Channel A voltage issue, audio signal lost on IC2.

[socialruins]

Hi everybody, I recently joined the forum and could use some help. I typically fly solo but this thermionic deluxe pedal is giving me a real headache.
I initially had it boxed and fired up, playing with the settings etc. Then, hit the channel switch. Nothing.
Channel B worked, Channel A was dead. So I had to unbox and start poking around. Unfortunately having to pull all channel B pots so I could have a look.
Here is some measurements I took:
IC1, IC3A, IC4A, IC2B, IC3B and IC4B shows pins 1,2,3 at 4.46V, pin 4 -8.81V, pin 5,6,7 4.49V, pin 8 8.5V.

IC2A if I understand correctly is the first gain stage of the signal and that's where it falls apart.
Pin 1 and 2 4.46V, pin 3 4.31V, pin 4 -8.81V, pin 5 4.46V, pin 6 -8.81V, pin 7 7.78V, pin 8 8.5V.
L1A stays on until turning gain all the way down.
Pins 1,2,3 and 5 pass audio when using a probe but IC2A.2 doesn't continue to IC3A.2 pin 6.
There is voltage of 7.78V going into the GAIN pot, L1A and L2A, etc.

My skill level stops here, I tried reflowing all solder joints, pulled and rebuilt the path between pin 6 & 7 with new components, replaced IC socket to check for shorts, and swapped the TL072 a dozen times. The yellow box caps are also replacements as I tried to find failed parts in the path. Hopefully more experienced eyes can point something out or could guide me to a spot on the board I need to look closer at.

Thanks for your help!

 

[Song Naga]

If the signal going into IC2A sounds like hot garbage then your bias may be off. I had this happen to my Thermionic Deluxe and found that I'd initially installed IC1 upside down and managed to cook it before flipping it round. My bias was shot until I replaced IC1 then it thing sung like a two channel platinum angel. MAYBE the same is happening for you. Check my posts about this here and best of luck!

 

[socialruins]

If the signal going into IC2A sounds like hot garbage then your bias may be off. I had this happen to my Thermionic Deluxe and found that I'd initially installed IC1 upside down and managed to cook it before flipping it round. My bias was shot until I replaced IC1 then it thing sung like a two channel platinum angel. MAYBE the same is happening for you. Check my posts about this here and best of luck!

Thanks! I found this post before signing up and it really made me confident that I was close to solving it. Unfortunately all voltages from IC1 look good, voltage paths to other ICs look good.
The audio sounds good and clear with varying gain levels between pins 1-5 but 6 and 7 die off. That gain loop is killing me.
At this point I’m starting to question the quality of the resistors nearby. R9 potentially. But I’m weary of pulling parts until I know for sure. They still test out at 22k on the soldered side too.
What’s weird is that it seems to die right between the output of IC2A.2 and the IC3A input. The IC3A side has 4.5V… lol
Even pulling the op amp from the socket I get my 8V on pin 8 and nothing on 7 so I would think those pins aren’t shorting out on the board.

 

[socialruins]

I finally figured it out. Started doing continuity checks and found that TRIM A was bad. Replaced the trim pot and it came to life.
Now back into my hole to build more…

 

[pafpro]

Hi @socialruins and @Song Naga I have some problems with my thermionics deluxe. Before opening a new thread, I thought it'd be better to talk to someone who has this pedal without a problem.

My questions are:

1) Are the knobs too or less responsive? The mid and treble knobs are too responsive; a slight touch changes the mid and treble way more than the ones on friedman be od deluxe. It didn't feel great, to be honest.

2) What about the bass knob on channel A? It doesn't work on mine. I replaced c12A, c13A, and ensured that R16A, R17A, and the BASSA are working. No shorts in the PCB. I considered the possibility that the IC doesn't function, but then I thought that if I hear the sound, the opamp does its job.


Also, the bass knob on channel B barely works. When I watch brown betty videos (it has the same bass control circuit), I was impressed by how the eq knobs worked great.

3) Apart from the knob issue, there is a ringing on channel B. I soldered everything carefully, cleaned the flux on the back panel using isopropyl alcohol. The knobs were cleaned and oiled with contact spray. I put a plastic separator behind each knob to isolate their surface from the pcb. Then I checked if a short circuit occurred, but no. It looks good, and I couldn't figure out where this ringing comes from.
From now on, I started believing that the only problem is the opamp (maybe more than one). Because when I finished the soldering, I accidentally dialed the tips of the power connections in reverse, which might have damaged them. I ordered new sets of TL072, waiting for them to arrive.