Super Drive 70s

[dhgagnon]

I’m having a really rough time with this one.

Audio passes through when none of the switches are engaged. However, nothing passes when any of them are engaged. I put together an audio probe, and it looks like the sound hits pin 3 on the IC, but I get nothing past there. I have installed a socket and tried 3 different chips, and still nothing. I’m not getting any voltage reading when I try to bias Q3 or Q5, so I’m pretty well stuck at this point.

Also, is this PCB discontinued? I spent several hours on this, and it would be really disappointing if I could not get another one to try again, in case this one is a bust.

[Billy]

It’s very difficult to make out any of your resistor colour bands even zooming in, you’d need to take a well lit picture without your hand covering some of the pcb so that colour bands can be clearly seen and all wiring traced

I can’t see most of your resistor 4th multiplier bands it’s difficult to see whether they’re brown, red or orange etc

Have you tried reflowing the IC socket solder joints

What voltage readings do you get on the IC pins and TR2 middle pin

Your soldering does look good but there’s always the possibility of a dry solder joint even if they look nice and shiny especially if they look ball like,  they could be dry inside

Just a note when audio probing you don’t always get a good connection with the probe I’d usually always check beyond where audio stops you’ve got audio at the IC input pin 3 and nothing on the output pin 1, I would normally check the input pin 5 just to make sure

 

 

[Author]

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