Like most DVM's, there is a relay between the terminals on the
front panel, and the internal circuitry. If that relay is not
closing... for whatever reason... you would have behavior like
you are describing.
I have found lots of relay failures on the sorts of reed relays
that are used in the 3456 and 3455. I would suggest looking
there.
-Chuck Harris
Bob Albert via groups.io wrote:
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How do I know if the tests fail?? It just presents the test number and that changes each time I press TEST.
My level of hope has been raised.? I think this is repairable.? Yes, Inguard to Ourguard communication seems to be the clue.? When I put a signal in it does not change ranges.? The Auto range takes it to the lowest range every time, regardless.
Bob On Wednesday, April 1, 2020, 11:18:39 AM PDT, Orin Eman <orin.eman@...> wrote:
Figure 8-H-1 in my manual shows where the assemblies and test points are.
Do all the tests 11 down to 0 fail?
I'd do the cal constant tests (Section 8-B-11), monitoring A10 TP4 () to see if the right voltages are getting to the AtoD.? Table 8-B-5 has the voltages to look for.? The procedure is a little tricky, but you are looking to see if A10 TP4 gets different voltages as you step through the constants at this stage.
If these voltages look reasonable, I'd look at the inguard to outguard communication - there are test points on A3 in the outguard section.
On Wed, Apr 1, 2020 at 10:36 AM Bob Albert via groups.io <bob91343@...> wrote:
Well Chuck, I don't know what to do next with this beast.? It acts as though it works but the display gives nothing useful.? Yet the display electronics seem to be working okay.
If I put a signal in, it ignores it.? Open or short on Ohms, voltage or no on volts, gives zeros and no autorange activity.? So perhaps it's an input circuit issue.? In Test I get error 11.? I press test repeatedly and it gives error numbers 10, 9, etc down to 0.
The manual sucks.? It tells me to look on module such and such but nowhere does it seem to show me which module is where.
Bob
On Wednesday, April 1, 2020, 10:22:56 AM PDT, Chuck Harris <cfharris@...> wrote:
Hi Bob,
I don't see how you can come to that conclusion.
The 3455A is highly reparable, and should be well
within your abilities.? Lots of people have fixed
their own successfully.
What you won't be able to do is send its calibration
module out for calibration.? You will have to do that
yourself.? But, it is not any more difficult to
calibrate than the 3456A.
It is not my meter of choice, as I greatly prefer
the 3456A, but for many, it is a useful addition to
their labs.
-Chuck Harris
Bob Albert via groups.io wrote:
? I don't see a whole lot of encouragement here regarding the possibility of getting my 3455A working.? Maybe I will just put it aside and wait for a scrap unit to swap out boards or parts.? My 3456A still works so I am grateful for that.
Bob
? ? On Wednesday, April 1, 2020, 06:40:17 AM PDT, Chuck Harris <cfharris@...> wrote:
? The 3455A was a dinosaur when it was first released.
The 3455A and 3456A were sold side by side, with the
3455A being about twice as expensive as the much more
capable 3456A.? The 3455A's interesting feature was
it was supposed to be cheap to calibrate.? All you
had to do to do a complete calibration was to unplug
the module in the back panel, and replace it with a
recently calibrated module.? The idea was you could
order up a calibration by mail, and return your old
calibration module as a core... never having to send
the full meter in for calibration.
Interesting idea, but surely not worth twice the price
of a 3456A.
I say it was a dinosaur, because it used all small
scale logic rather than large highly capable hybrid
circuitry, like the 3456A.? It should be much easier
to repair, but it should also be much less reliable.
And, that is my experience with the two units.
-Chuck Harris
paul swedberg wrote:
With respect to the 3455 and 3456 the difference is night and day. I have
numbers of 3456s and was given a seriously troubled 3455. Quite a
interesting meter.
Replaced at least 11 actually malfunctioning chips on the logic board. The
logics simple so easy to verify the chips were bad. No shot gunning
involved. Never really did get it working but ended up with a different
3455 that needed help and the AC board and it is in fine shape. With
respect to the old 3455 it has both a logic and voltmeter issue. The 3455
uses an unusual processor and teh DVM uses the same proc and a masked eprom
that is known to go bad. It acts as a state machine.
The 3456s are losing there eproms and copies can be found on the net. Thank
heavens.
Regards
Paul
WB8TSL
