3rd build, first problems, VCA wide open no filter action - CEM3379

whilst assembling my 3rd shruthi-1 build today (my second CEM3379) I noticed when I plugged it in that the power supply section heated up rather fast to an abnormally high temperature, audio into the mixer showed that it was outputting a constant tone regardless of any MIDI input - pretty dang sure it’s not the digital board - I had it hooked up to another filterboard to test it after I flashed the atmega although it has been sitting on my table for a while gathering dust - will re-check it for happiness points if/when I am more frustrated and awake than I am now

I’m just a hack with a soldering iron here, not sure what I should be looking for in a voltage test or where I might start looking for problems - audio was coming out and changing oscillator params and such would change the sound slightly but it seemed like the filter didn’t seem to be doing anything when I swept cutoff/resonance which makes me want to check the CEM3379 chip first… but maybe the VCA being jammed open is a bad cap or something?

what sort of voltages should be coming off the pins of the CEM3379? I don’t fancy pulling the one out of my other (working) unit to test if it’s the problem

thanks all! . . . learning how to fish but sometimes you’re just hungry ya know? ^^

Do you have a scope?

Remove the CEM3379.

What kind of signal is there on pin 1 of IC4?

no 'scope here just a multimeter - there is no other way to check the filterboard w/out the CEM3379 in there? . . . I do want a 'scope though, quite likely to need it for future projects, any suggestions?

I suppose I can stick the ‘suspicious’ CEM3379 into my working CEM3379 filterboard to verify it - it’s not like a bad CEM3379 is going to blow up other parts on the good filterboard (?) - I am very hesitant to stick my good CEM3379 into the ‘suspicious’ filterboard only to let out its magic smoke

if your psu section is getting very hot much quicker than normal there could be some short somewhere. have you checked your voltages? but your digital board worked?
don’t put such an expensive chip in there as long as you’re not sure everythings fine

all fixed up now, the CEM chip was just fine

filter was not responding to Q or cutoff controls due to a poorly cut 8x1 connector between the two boards

It’s likely that the VCA was jammed open due to one or both of a couple caps (C3 and C4 not sure which, I replaced both at the same time) that I probably damaged when bending them down to the board (accidentally soldered them with too long of leads and had to bend them down so they wouldn’t smack into the atmega that’s overhead on the digital board) after verifying the CEM3379 was good by sticking it into my other CEM3379 build those caps were next on my ‘highly suspect component’ list and promptly were replaced - after replacing them the PSU did not abnormally heat up and there was no longer a constant LOUD tone coming out - I then discovered the connector problem (cut that connector months ago and should have looked at it more closely when piecing things back together)

still need a 'scope though, but now it’s full steam ahead on the enclosure!