Vintage Synth Repair

I tested the transformer last night. I'm getting 2x 15 volts, which is good, and the transformer is working great, no shorts or fused cores. Oh, how I wish it was just the transformer...

While I had it open I swapped out the 4 voltage regulators, still same problem. It was worth a shot!

For some reason I think it has to do with OSC A and OSC B reaching the VCA. It seems strange that BOTH would go at the same time, so hopefully there's no bad CEMs in this thing. I'm about to send it to Greg Montalbano of http://www.analogsynthservice.com/ if I can't get it working!


--- In vintagesynthrepair@yahoogroups.com, "GB" <grantbt@...> wrote:
>
> How are the power supplies?
> 
> GB
> 
>   ----- Original Message ----- 
>   From: Mark 
>   To: vintagesynthrepair@yahoogroups.com 
>   Sent: Wednesday, May 04, 2011 10:35 PM
>   Subject: [vintagesynthrepair] Sequential Circuits Pro-One not working... Please help!
> 
> 
>     
>   I recently bought a non working Pro-One locally, and I decided to open it up and try my hand at repair. I've repaired quite a few synths, but this one has stumped me. I've had a Pro One in the past, and sold it years back. It looks like the previous owner had replaced all the film caps for red Panasonic poly film caps.
> 
>   Anyway, what's happening is this:
> 
>   When the unit is plugged in, there is no output. There is output when you bring the noise knob up in the VCA section. No output on OSC A or OSC B. Also, master volume is not working, the volume stays the same throughout the rotation of the knob. The volume is very quiet. I have to turn the gain almost all the way up to hear it on my amp. There is a faint hum in the background. Key presses are working, as the gate LED lights up. LFO is working, as it drives the gate LED when the repeat switch is on. The envelope section has no effect on the noise either. I feel like this may be either a bad trace or perhaps a bad IC? Hopefully not the processor!
> 
>   Another important note is that the external audio in is working too, but is unaffected by the filter and shares the same volume issues. I think this may be a VCA issue. Is that possible?
> 
>   Any direction would be appreciated, as to where I should be looking. Any obvious areas of interest I seem to be skipping over? I really would like to get this working!
>