On Nov 8, 3:16 pm, "robb" wrote:
wrote in message

ps.com...



On Nov 8, 4:49 am, "Arfa Daily"
wrote:
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.

umm.. i think you lost me,.... yes yes this place is familiar it
is "lost land"

Ignore all that.

1. As Arfa suggested, isolate the L387 output from the 5V rail.
(Probably doesn't matter if you lift Pin 5 or disconnect some
other way.)
2. Replace the 5V fuse (and only that fuse? or do you also need
the 30V fuse to feed the L387?).
3. Power up.
4. If the fuse didn't blow, measure the voltage from Pin 5 to Pin 3
of the L387 (5V OUT to GND).
5. If you got ~5V, reconnect the 5V rail and test again. If not,
connect a 470-1k ohm resistor from Pin 5 to Pin 3 and test again.
6. If still no 5V, measure the voltage from Pin 1 to Pin 3 (Vin to
GND)
- it should be ~30V.
7. If ~30V was present on Pin 1, the L387 is bad. If not, the 30V
bridge is probably bad.
8. If the fuse(s) blew, test the resistance of the bridges.

TM