On 2015-Aug-01, at 1:26 PM, Eric Smith wrote: > 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.
Just a suggestion: you're sure there no ground reference problem on pin 7 (V-) of the 723? (hence raising the Vref). I've seen small 723-based supplies with sense leads where the 723 V- is on the neg. sense lead rather than neg. output lead.