1 Aug
2015
1 Aug
'15
1:14 p.m.
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.
available, but due to the construction of the power
supply, replacing
it is relatively difficult. Just probing the pins of the chip was a
challenge. The pass transistors are mounted to 1/8 inch aluminum
plate, but the pins are soldered into rivets in the single-sided PCB,
Ouch, that sounds horrible to work on.
One thing... I had a (SMPSU) that seemed impossible to work on, it was built
a bit like that. Then I found that those 'rivets' were actually sockets and the
transistors were plugged in, not soldered. All I had to do was unto the
mounting screws and it all unplugged. Of course I didn't realise this and
spent some time desoldering things.
I assume you have proved your pass transistors are soldered in place.
-tony