Different Duo Phase issue (different builder too :) )

[geekmacdaddy]

Phasor A's LFO isn't pulsing, bulb is on. Interestingly enough, the charge pump is heating up as if it were in backwards, or the position of Electro's and or Diodes were wrong, but none of that is true. Looking for solder bridge but there is none. Please help?

Thanks
Geek

 

[Chuck D. Bones]

What's going on there with R34A? Does the Channel A Feedback pot have a dust cover?
Sounds like the -9V rail for Channel A is being loaded down. Measure the -9V rail to confirm. The only parts that draw current from -9V are the opamps. Do any of the Channel A opamps feel warm? Try pulling them out and see if the -9V rail comes back. If the -9V is still messed up, turn off the power, remove IC7A and measure the resistance between -9V and ground. I'll bet you find a short. Sometimes, solder bridges are very difficult to see. Try more magnification and different viewing angles. Look for debris on the component side of the board. It's also possible that there is a manufacturing defect in the PCB. Good luck!

 

[geekmacdaddy]

Thank you for the help, Chuck! R34A (btw, I was incorrect, it's the B channel) is cool. Didn't have a 120R so I made a 110R Teepee with what I had. Yes, there are dust covers on the feedback pots. I checked for other heated IC's and lo and behold, IC 6B was hot. I replaced it and Bam. Bad TLO72. All better! I am getting a "Ticking" in the other channel. In time with effect when engaged, but there in bypass as well. In bypass, if you turn rate down, the clicking levle responds.

 

[Chuck D. Bones]

It looks like C19B got nicked by the soldering iron, maybe it's damaged internally? These types of LFOs are inherently noisy because the output of IC6.1 switches quickly and slams against the rails. Power supply bypassing is pretty minimal, which doesn't help the situation. You could try tacking 100nF caps from IC6 pin 8 to pin 3 and IC6 pin 4 to pin 3 on the offending channel and see if that helps.