[sdiy] newbie question, ua723

[Ingo Debus]

Rob Mantel wrote:
> The 5V output of my old b&k 1650 tri output power supply suddenly stopped
> working. No more output. When I opened the thing I found that it uses a
> ua723 regulator for the 5V output. Since I had a couple of those laying
> around I replaced it, and for a minute was happy because, yes, the 5V output
> was 5V again.
> 
> However, 1 minute later again I wasn't happy anymore, because I found out
> that drawing more than a couple of mA from it makes the voltage drop to 0.
> Looks like there is more wrong.

Power transistor fried? It's possible that the regulation still works if
the current is very low.

Another reason could be the current limiting feature of the 723. Look if
there's a low-ohm resistor (lower than 1 ohm) in the circuit and check it.

Ingo