Tyrian issue

[Endosidney]

After successfully troubleshooting other builds, this one has baffled me. So gain pot and the mid pot do not function. I get a fairly gainy, even pleasant, signal but only the vol pot controls it. Interestingly, I get 4.45v on each of the mid and gain pot legs. Also, I’d replaced the gain pot and noticed that I still get same signal whether gain pot is installed or not. ICs seem to measure ok. I can’t seem to find any bad joints or values. Clearly I’m missing something though!

 

[temol]

Make sure you have a continuity between pin 6 of the IC1.2 and R17. Same with R17 and pin 1 of the Gain pot. Then Pin2 of the pot and IC1.2 out.

 

[Endosidney]

Thanks! No continuity between pin6 and R17. However continuity between the other two listed

 

[temol]

So now you can:
- inspect the pcb.. is there any missing solder joint? Or maybe cold solder joint?
- resolder those two solder joints
- if above fails - you can solder some wire bridge between pin 6 and R17.

 

[Endosidney]

Thanks so much for your suggestions. A jumper from pin6 to R17 resulted in a sputtering gated mess despite any position on gain pot. Given that and the mid pot dysfunction I have a feeling we’re dealing with multiple issues. Nothing I’ve done, from reflowing, changing ICs, cleaning, staring and more staring, has made a difference. Perhaps it’s a wrong resistor value somewhere. I believe the caps are correct tho. I don’t regret the time I’ve spent since it’s always an opportunity to learn but I think I’ll shelve this one for a bit and move on to another

 

[temol]

Make sure R16 is 33k. Should be orange-orange-black-red, but to me it looks like orange-orange-black-brown which is 3k3.