1 Aug
2015
1 Aug
'15
1:26 p.m.
On Sat, Aug 1, 2015 at 2:14 PM, tony duell <ard at p850ug1.demon.co.uk> wrote:
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.
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. 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.