SCI Pro One oscillator range won't go low and extremely long warm up time
2014-12-28 by Gregory Cox
Hello, I’m trying to figure out this cursed Pro One I accepted for repair. I’ve brought it back from death and have sorted out all the problems it had except this one has an extremely long warm up time and the oscillators just stop oscillating below a certain point. One night I had it completely tuned up and everything was great except the low setting didn’t go very low and stopped halfway through sweeping the pitch. Next day I turned it on it took a very long time to warm up again(like half hour or more) before it could do anything musical. The scaling seemed odd as low notes needed to warm up before they’d be in range to start working over the point where the pitch drops out. I thought it may have been a flux residue issue so I cleaned the board both sides with flux remover and then alcohol but made the problem somehow worse. Not sure how this could be possible. Most parts are new, as I tried swapping out the DAC and 3280 amongst other things... I put new 104 caps in at some point during the troubleshooting phase, I’m not sure if this is the problem or not but I used ceramic capacitors as that is what I figured the old yellow .1uf ones were. Not sure if the originals were a special type of ceramic or film but I got ceramic ones that looked somewhat the same. I tested the CEM chips in my OB8 which work fine. The power supply is completely rebuilt and the voltages are what look to be correct (ie. just slightly under 15v). All new 348 op amps and TL072’s(old rev). Been looking over the board a million times and can’t see any trace cracks, tested power traces to every IC which check off with continuity. Anyone have any ideas of what area I should be suspecting here? I feel like I’m running out of things to try, and any advice would be greatly appreciated. Regards Greg C