DIYbanter - View Single Post - troubleshooting method for micro-controller board ?

Eeyore

wrote:

On Nov 8, 4:49 am, "Arfa Daily" wrote:
Well, I would have to say that it certainly indicates that you are not
chasing down any kind of permanent 'short' on your 5v rail. So now that you
know where the 5v rail comes off the end of the LM317 (was it ?), can you
disconnect it from that point, leave the fuses out of the 12 and 30v feeds,
and hook the unit back to line power, with a 5v fuse in place ? Measure the
IN, SET and OUT pins of the '317 to see what you get, and if you get a
correct 5v on the OUT pin[...]

If the voltage isn't correct (e.g. 4.8-5.2V) at that point (but the
fuse isn't blown) tack a 470 ohm resistor from the OUT pin to GND. The LM317
has a load regulation spec of 10 mA, and a minimum operating current of
~1mA (for low Vi-Vo); the adjust resistors may not be small enough to draw
this much. And don't isolate the regulator by lifting the OUT pin, or
you'll lose the adjust resistors.

It's not an LM317 though, it's some funny STM part, an L387.

Graham