HP 34401A not measuring after storage, for a moment

[m k]

The machine was on its side few months, power side down.

After turning it on it didn't measure DCV nor Ohms.
Switching front/rear didn't change anything.
Checking with other meter Ohms had no voltage.
Trying DCV with a resistor dropped reading down.

After a minute or so later everything was fine.
Still is.

What happened, a contact problem?

[AVGresponding]

Sticky COTOs? Lazy coils?

[Whitefoot]

Only a guess. Maybe the dielectric of an electrolytic capacitor needed some reforming. Leaving the meter on for a day or two would more thoroughly reform the cap.

[AVGresponding]

Only a guess. Maybe the dielectric of an electrolytic capacitor needed some reforming. Leaving the meter on for a day or two would more thoroughly reform the cap.

That shouldn't affect measurements. If there was a DC rail problem or noise on the signal path I'd expect an error code.

[m k]

This morning both meters, problem and checker, were 0.0 VDC.

The house have a tendency to drop certain phase when grid blinks.
Stove has a clock, it's fine, but it usually doesn't see the blinking.

Now checker meter is in Ohms and the problem one is VDC with manual range.

I've never experienced relays that are very intermittent.
But reed types are replaced shortly and older styles operated somehow, even filed.

After a second thought the storage is interrupted around a month ago.
No problems then.
Now temps are up and possibly moisture also.

[AVGresponding]

I'd check inputs and outputs of K101 and 103. It isn't uncommon for relays to fail; I've a Solartron 7150 with a failed relay in the input conditioning (contacts welded, like that when I got it), which causes the 2V range to overrange. I do have some replacements, but procrastination keeps me from getting a round tuit.

[factory]

Only a guess. Maybe the dielectric of an electrolytic capacitor needed some reforming. Leaving the meter on for a day or two would more thoroughly reform the cap.

That shouldn't affect measurements. If there was a DC rail problem or noise on the signal path I'd expect an error code.

Don't know what your experience has been like with these, but my older 34401A had some rails for the AC/frequency functions shorted by tants, no error codes are shown, unless you manually run the self test and that didn't tell me anything I didn't already know.

David

[m k]

Must try the self test.
(Done, no problems)

Before any inside checks I'd like to have a third situation.
Generally problematic relays(or caps) are nothing new, I predict I have few around problematic Fluke 8505A modules.

So the pair is moved to be aside and their functions swapped.
No idea what phase of electricity is where around the house, but missing manual range will reveal the blinked grid.

I remember reading that after longer storage session the machine must be on for several weeks before it's dried.
But I guess that's for least significant digits.

User guide states that high humidity affects only accuracy.
So I guess the machine must be dripping before anything major should happen.

User guide is also silent about the orientation of the machine.
Maybe I'll put it on its side after few non problematic days.

A side note about readings.
The other machine is Fluke 8860A and its reading is fluctuating few ticks when 34401A is dead steady.
But fluctuating is around a decade limit, so can be just bad luck compared to HP.

[m k]

HP has now been on its side for several days.
Grid also blinked one day.
HP doing Ohms didn't notice, but Fluke was back to auto range.
Nothing special after that.
Mode change every now and then, and some tapping and rocking.
No problems.

So the decision, I'll put it away for few months, original place, original position.
See you in a near future, stay tuned.

[m k]

Quick test, no problems.

One of those blue moon moments, it seems.