Yeah, your scope connection will be with the ground connection of the probe
going to power supply return (most likely connected to the case, but not
always) and the probe tip to the circuit point you're monitoring. if you
saw no ripple there, then the PS is probably OK.
How long has this unit been out of commission? Is it possible that it a
lightening strike or power surge may have caused its demise? If so, then
it's possible that most, if not all, of the semiconductors in the unit are
bad. If the sensors are outside, and close to a power line or phone line,
then it's possible that may have been the cause of failure.
It's going to be a bit difficult to diagnose it without a schematic to
reference, but if you can adequately describe the circuits and their
symptoms, then we may be able to get it going again. I searched all the
usual places for freebie downloads, but no joy. +
Cheers!!!!!!!!!!!!!
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!
"tempus fugit" wrote in message
...
The PS voltages were the 1st thing I checked. They were pretty saggy, so I
replaced the main filter caps. That helped, but didn't fix the problem, so
I
moved on to the regulators, and found that the -15v regulator was out of
commission, so I replaced it. This improved matters somewhat, but there
were
still problems, so I kept poking, and found a shorted PNP on the CPU
board,
which I replaced.
I have a scope, but am kind of new to it. I basically attached the ground
clip to the case and probed the regulator's output, which showed no ripple
(which seemed a little unrealistic to me). Is this the proper method for
checking for ripple?
As for the tarnish issue, I'm just going to check for continuity from the
IC's pins to the connections on the solder side of the board.

Thanks again, and keep those suggestions comin'


"Tweetldee" wrote in message
...
You don't need to worry about the tarnish on the soldered component
leads..
just the socketed components, such as ICs and transistors. If there are
any
connectors that appear to be tarnished, then you should clean those as
well.
BTW, have you checked the power supply output(s) with your multimeter?
If
the supply voltages aren't correct, then you can't expect the rest of
the
circuit to operate properly. How abot ripple on the PS lines? If
there's
a
lot of ripple, then there will be all sorts of chaos in the circuit.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in
the
address)

Never take a laxative and a sleeping pill at the same time!!
"tempus fugit" wrote in message
...
Thanks again.
Unforunately, I don't think I can scan the schem (it's huge for one
thing).
As for the voltages, they don't match up with what's indicated on the
schem
in a lot of places (even when I had most of it working), so I don't
know
which to trust. I'll try removing the tarnish and checking for
continuity
though.
Thanks


"Tweetldee" wrote in message
...
"tempus fugit" wrote in message
...
Thanks tweet.

The black stuff is actually on quite a few of the components -
diode
leads,
resistors, ICs, etc. I never really looked too close at it, but it
almost
looks like black paint.
The opamps are HOT. They start out cold, and after about 2 minutes
are
too
hot to touch. I have the original schematic, as well as the
manual,
but
have noticed some errors on the schem (or the circuit board, I
don't
know
which). One thing that I have noticed on a lot of components
(mostly
xsistors) is odd voltage readings. There might be 5v on one side
of
a
bias
resistor, and 0.3v on the other (xsistor) side, but the xsistor
checks
out
OK with a diode test (i.e., not leaky or shorted).

Thanks



From your description, I'd guess that your problem is
intermittent,
and
may
be easily repairable.
When you say that there is "black stuff" on the pins of the
4066,
is
it
just
tarnish or something else? If it's tarnish, then that could be
the
majority
of your problems. I assume that the ICs are socketed. If so,
you
can
use
any of a few methods to clean the tarnish off the pins. The
quickest
is
Tarn-X, but you have to rinse them very well afterwards with
clean
water.
Don't leave *any* Tarn-X residue on the pins, since it is
corrosive.
Another cleaning method is with a rubber pencil eraser. Be
careful
with
this, since it is easy to bend/break the pins.
What condition are the IC sockets in? They may need to be
cleaned
or
replaced if they are in bad condition.
How hot are the opamps? Are they just warm or really hot? If
they're
just
warm, it may be normal, depending on the circuit. Opamps
usually
are
low-level components... that is, they don't handle any
appreciable
power,
and usually run pretty cool.
Is the schematic of the unit available on the web anywhere, or
can
you
post
it to the binaries NG? Might help with some suggestions to help
you.
--
Tweetldee


Undoubtedly, the "black stuff" that you see on the leads is tarnish.
It's
not dangerous to the components, but if it's interfering with mating
of
component contacts, it will certainly prevent the circuit from
operating
correctly. This could be the problem with the opamps.
There's something seriously out of whack if the opamps are too hot
to
touch.. Don't allow it to run for more than just a few seconds
until
you
get it fixed.. the opamps will be destroyed, if they are not
defective
already.
I can't tell a thing from your voltage measurements without seeing
the
schematic along with the voltages. It certainly would be a big
help
if
you
could scan the schematic and post it somewhere. Without it, it's
pretty
much a waste of time here.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters
in
the
address)

Never take a laxative and a sleeping pill at the same time!!