diagnosing an Intel Series II MDS monitor failure

[Eric Smith]

On Sat, Aug 1, 2015 at 2:14 PM, tony duell <ard at 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.