[sdiy] SCI Pro One 15+ power rail

[rsdio at sounds.wa.com]

On Aug 26, 2013, at 07:29, Csaba Zvekan wrote:
> I'm troubleshooting a SCI Pro One and have a problem with the 15+  
> power rail as I'm measuring the voltage regulator 7815. I get a  
> value of  -0.6V on a positive rail.
> Does that mean I'm having a short of some sort on the many OP-Amps  
> and CEM's etc that tap in that rail ? Any help or suggestion on how  
> I should continue to troubleshoot would be  greatly appreciated.

If you suspect a short on one of the ICs, then the quickest test  
would be to disconnect the power transformer and see if the voltage  
returns to +15V. If the power supply doesn't work on its own, then  
you know what to fix. I haven't opened my Pro One in a while, but I  
seem to remember a molex connector for the power. I don't remember  
whether the regulator is on its own board or on the main board.

I also can't remember whether any of the ICs besides the CPU are in  
sockets, but if they are, and the power supply is capable of +15 V on  
its own, then you could try removing all analog chips. While removed,  
and without powering anything up, test resistance from power to  
ground on each chip - if the chip is bad then the resistance might be  
rather low (under 100 k), but if it's good then the resistance should  
be very high (over 1 M). On that note, before removing any chips, you  
could test resistance between the +15 V rail and ground to see if  
there is a short.

Brian Willoughby
Sound Consulting