Without seeing the schematic, it's a hard call as to whether the TL074 would
be a good replacement. I haven't looked at the spec sheets of either unit,
but I do know the the TL074 is a JFET input amps, whereas the LM324 is not.
I assume the pinout is the same.. you will need to check that out.
Probably wouldn't hurt anything to try the substitution, but couldn't
guarantee they would work.
Is the CPU in the unit a programmed chip or does it have a PROM/EPROM/EEPROM
to store the code? If it's a programmed CPU, then you might surf around on
Google to see if there are any replacements available. The switches that
are used to set the time/date, etc, may be tarnished and not making contact.
Check all of the switches for good, solid (not intermittent) low-resistance
contact.
But, going back to the original problem, I would continue to look at the
areas that may be affected by the tarnishing of the contacts on IC's,
transistors, or any other components that may be socketed. Also, you
should look for components that are loose. Sometimes, the plating on the
leads of components comes off, and effectively breaks the connection. If
there are any suspect soldered connections like that, then do the obvious
and resolder them.
--
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
...
Yea, it does keep track of the time and date, but I can't actually set
these
parameters. Maybe I'll try replacing the ICs and go from there. The opamps
are LM324s. I've got a spare TL074 around - do you think this would be an
OK
replacement, or should I replace them with the originals?

Thanks again


"Tweetldee" wrote in message
...
If you plugged the 4016 in backwards, then it's probably damaged..
replace
it for sure. The 4066 can be used in place of the 4016, with better
performance in some applications.
As I said in an earier post, opamps usually don't run hot, or even warm.
If a new 4016 doesn't fix your problem, you might replace those opamps
and
see how it works.
Does the unit keep track of time and date? If yes, then you may have a
Y2K
issue with the date display, but I doubt that could be causing your
operational problem. Worst case, the date would be wrong, probably
jumping
back somewhere in the 1900's.
--
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
...
Once again, thanks for your reply.

I have no idea how long it has been dead. My brother in law got it for
free
(!) at a garage sale this summer, and was told that it was working.

I was messing around with it again tonite, and I noticed a gross
error.
Remember I said I pulled a 4066 out because the voltage readings were
way
off from the schem? Well, it wasn't a 4066, it was a 4016, and (this
is
the
embarrassing part) I had put it in backwards when I reinstalled it.
Anyway,
the good news is that (now that it is in the right way) the opamps are
running at a normal temperature (slightly warm). I'm wondering though,
if
that part isn't screwed (the 4016) because when I say the voltages are
off,
I mean the wrong polarity as well as the wrong voltage. Maybe I'll pop
a
new
one in and see what happens.

Here's another thought: this thing was designed in the 70's, so maybe
the
CPU has a Y2K problem. I found a site that mentioned that the time was
an
issue because of this for this unit, but it didn't describe the
symptoms
I've got.


"Tweetldee" wrote in message
...
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!!