Robert Baer wrote:

Jamie wrote:

JW wrote:

So there you are, working on something that you don't have any
schematics
for; (in this case a Datron 1281 8.5 digit DMM) This one wouldn't power
up. Poking around I noticed some (TTL) circuits were not getting +5VDC.
Traced it back through a three terminal linear regulator to it's AC
input.
Hmmm... Only getting about 5.5VAC, not enough there. Isolate the AC
output
from the transformer to make sure it wasn't a loading issue; it's not.
Gets to about 5.8VAC. This unit has two toroid transformers, and the one
I've traced the problem to has 8 wires on the secondary and another 8 on
the primary (sheesh)

I have no idea what the primary voltages should be (As it turns out,
about
16VAC. Weird!)

BUT, suddenly I hear a metallic sounding "tick!" and the unit begins
running. (I quickly measure the primaries and note the voltages JIC.)
sounds a bit like a relay, but there's nothing like that in any of the
power supplies (there's a number of them) that I can see. Figuring an
intermittent somewhere I begin jiggling connectors, tapping around
with a
screwdriver handle, etc. Nothing. Meter keeps working.

Cold blasts from freeze spray, Heat gun, etc. Nothing.
Turn it off for an hour and back on repeating what I did above. Still
working.

Turn it off for a day and back on. Wash, rinse, repeat. still working
perfectly.

Things like this seem to happen to me often. Is it just me, or do you
have
faults like this that drive you nuts?

I don't suppose anyone might have any schematics for this meter, would
they? I think at some point Datron sold off to Wavetek then Fluke
ended up
with it, as the user manual is available from Fluke.

Thanks.


Electrolytics will intermit like this. Change all that are in the
power supply section.


Yah, i have run into wierd operation / no operation; back and forth;
more than enough to drive anyone nuts (maybe that is why i am so weird?)_.
At one place i worked, there was this HP programmable automatic
tester, tied to (an added) keypunch for data logging.
Worked for months then stopped working.
Started signal tracing with a VOM starting at the keypunch.
Back in those dayz that is all the was, but i would have chosen to use
a VOM over a DVM so i would not miss data pulses.
Got a few feet from the keypunch solenoids to input connector and then
(no sound) it worked; for weeks.
Next time it failed, i checked the cable from keypunch toward the ATE,
but it immediately started working as i started the cable test AT the
keypunch; worked for weeks.
Next time, i started with the interface circuitry at the ATE; you
guessed it - 15 seconds later it worked; yup! for weeks.
And so on; testing creeping to the middle: the cable.
Never got there; was about two inches away from the cable connector at
the ATE the last time i tested the beast.
Never failed again.

All you can do, is leave the damn thing alone as long as it is
working, ignore the hassles, forget them and go on.
But to keep Mister Justin Case mollified, do not totally forget what
you did so that you can pickup the testing gauntlet where ever you
previously left off.

We had a coil in a reversing relay that would intermittently not work
and cause the mechanical drive train to push off in never never land,
thus damaging some very expensive rotor cones. It finally got bad enough
at one point where we were able to fine it.

It turns out that this "GE" reversing contact assembly used pushed on
spades in side to make it's wire termination to the coil instead of
soldering them!. And you had to unassembled parts not intended to be
unassembled to find this. The mechanical vibration of the unit would
cause a connection issue and not switch on the coil for the reverse
operation when needed... The other controls would just keep cranking the
motor trying to find the correct location when it was actually pushing
it out of sight! And no, there were no limiting sensors in this machine