On Sat, Aug 1, 2015 at 2:14 PM, tony duell <a...@p850ug1.demon.co.uk> wrote: >> The root cause of the failure appears to be that the internal voltage >> reference of the uA723, which is specified as 7.15V ±0.35V, is now >> 9.4V. The uA723 needs to be replaced. The uA723 is still readily > > That's an unsual failure. I've had 723s go internally short-circuit and > then the output voltage is essentially the input voltage, but never > seen the reference drift.
The circuit used in the PS only ties the reference output (pin 6 of the DIP) to the non-inverting input of the amplifier (pin 5), so I don't think there's any other likely explanation, though since I haven't actually been able to pull the board out yet to inspect it more closely, I suppose there might be a very small chance of something else being shorted to those pins. > I assume you have proved your pass transistors are soldered in place. It sure looks like solder joints, but I should double-check. I was surprised by solder joints on the top (non-etch) side of the single-sided board, but I've been told that Power-One sometimes installed rivets into the PCB holes for that.