Pythagoras/Unison: mix full clockwise = no output signal

[Plate of Shrimp]

The initial power-up for this build was totally silent until a voltage check found an open on FV-1 pin 13 and an open at the stomp. After addressing those, all FV-1 pins return voltages that look plausible according to my interpretation of the schematic. When Mix is counterclockwise, Volume works and signal sounds clean, if boosted. But Mix at full clockwise kills output. How easy is it to thermally fry the FV-1?

There's probably other probing that could be done over and above a voltage check across the PCB.

 

[Bricksnbeatles]

Have you probed to see if audio is reaching pins 1&2? If it’s not, your issue is elsewhere. If it is reaching 1 & 2, probe to see if anything is being output from pins 27 & 28— if you’re not getting anything there it could be that the FV-1 died

 

[Plate of Shrimp]

Duh. Well played. Once i find my scope leads...

 

[Plate of Shrimp]

Signal seems to make it to pins 1 and 2. Mostly nada from pins 27 and 28.
I'll blame poor soldering first then burning things second.
Thank you for playing.

 

[Plate of Shrimp]

It was there so poked at it again...
IC2 pin 5 -> IC3 pin 15 passes continuity check.
IC2 pin 6 -> IC3 pin 14 fails continuity.
IC2, IC4 and R13 get first-degree-burn hot after 15s of powerup.