HP 3455A 'special' parts?

[GregDunn]

Back in the days when I was doing test/evaluation at my job, we had a pile of HP test gear all connected to our 9825A controller.  The centerpiece was a big new 3455A which was a pleasure to use.  Given that they seem to be relatively available, I'm thinking about buying one for my lab.  Partly sentimental reasons, sure - but it was such a nice meter and I really would like to add one as the centerpiece to the bench.  Literally - I know how big they are.

I've read all the repair threads here, and it looks like most of the issues are relatively straightforward to repair.  The manual only shows a couple of possibly unobtainium parts - the processors and transformer(s).  But it doesn't seem as though those are items which fail on your average 3455A.  Yes, maybe it will take a while to go through all the troubleshooting steps, but it is mostly op amps, 7400 and CMOS, which are available.  Plenty of them, though, for sure.   

I'll pop for a working unit if possible, but it doesn't seem that even a typical repair is that bad.  Are these units likely to be sold with missing boards?  What else do I need to be aware of before buying one?

Thanks for any suggestions.

[Tim T]

Most ebay sellers only check for power up without going to trouble of plugging in and shorting some leads or applying to a power supply or battery or resistor. So most likely the only photo will be of DCv noise. Just now fired up my 3455A with no leads and it starts out at about 1.5v  and drops to 500mV after 5-10 seconds, 400mV after a minute then 250mV after several minutes. Not much here, but hope it helps,

Bought this 3455A about a year ago with only a photo consistent with above. In a way was hoping for a repair project, had the lousy good luck of a fully operating unit at least as good if not better than all my other DMMs though due to size it also excels as a table - hmmm - might be on to something here - a few legs and a Plexiglas top and this will be an at least  $1500 piece of techno art.

tim

[GregDunn]

If I understand correctly, even displaying DCV noise digits means that the display, inguard and outguard boards are talking to each other; I know the test function doesn't test ohms and ACV.  It might be giving poor readings, but that's still a hopeful condition.

I won't complain too loudly if the unit shows up in fully operable condition.  But as with other purchases, I intend to be as sure as possible that it does power up if I'm paying more than a few bucks for it.  Fingers crossed, so far I haven't gotten a lemon yet - expecting some refurb will be required does cut down on later disappointment.

Will the unit even power up if a board is missing?  I guess that's my greatest fear, knowing that some Fluke meters are known for being sold with missing boards.  I wouldn't consider an incomplete unit to be "operable" but the seller might be deceptive?
 

[Tim T]

By no means an expert, my understanding, somewhat confirmed by a quick look at the operating/service manual, is the 3455A did not offer plug in options while for Fluke bench meters of the day that was fairly common. So one reason for board pulling should not exist for the 3455A.

Perhaps I have been lucky, but not one of the 20 or so pieces of 20-40 year old mostly HP (a little bit of everything) and Fluke (primarily lower grade bench DMMs)  equipment obtained from US sources through on line auctions have been missing boards or parts. It might be that equipment of that era was made for and expected to be repaired at component level rather than swapping boards (along with the detailed manuals is why I like to use this old stuff as learning tools), and after years of service it eventually did fail or was obsoleted there was no value in trying to repair (or pay for calibration - hint here - look for a somewhat recently expired cal sticker) so it was tossed on a shelf intact rather than cannibalized.

tim

[pelule]

Having refurbished/repaired several of 3455A (and other vintage HP gear). Still have one 3455A in a very good condition.
Never the less I would recommend the 3456A (similar function, but more modern design)
In general you are correct:
If the tool has an operating display (shows measurements) the basic system operates.
Thus most "HP specific parts" are operating (at least for some time).
You have no evidence, the system has other issues, for example leakage or temperature depending problem.
Just 2 out of my list of 3455A problems:
- CPU failed after warm-up, operates if I cooled it - a very rare issue, but I had to replace the CPU (search the bay).
- switching FETs in the analog section failed after warm-up due to high leakage - need to be replaced
I recommend to request the seller to let the system run the selftest for at least 30 minutes and to report the result.
There is NO need for knowledge or specific equipment. Thus, if he does not accept - run away as fast as possible.
/PeLuLe

[pelule]

By no means an expert, my understanding, somewhat confirmed by a quick look at the operating/service manual, is the 3455A did not offer plug in options while for Fluke bench meters of the day that was fairly common. So one reason for board pulling should not exist for the 3455A.

That's not fully correct. The 3455A was available with 2 different AC/DC converters
- an Avarage AC/DC-Converter board
- an True RMS AC/DC-Converter board
That boards are part of the shielded analog part, thus not easey too remove. And if removed, the DC/Ohm still operates.
Mots critical here is the reference assembly, its is easy to remove and often used to build a DIY 10-V reference
I once had a 3455A with just a simple 10V Z-Diode instead of the reference assembly 
/PeLuLe

[Kosmic]

The fan in the 3455 might be a problem if it break. It use 3 phases voltage and not normal DC. Another good advantage for the 3456a which is fanless (in later version).

I had both for a while and decided to keep the 3456a. It was just rock solid while the 3455a was a little bit more volatile.

[GregDunn]

Thanks all - good info.  I fully understand that the 3456A is a better choice for use as a meter; I will hope for one of those at a reasonable price.  If I find only one at the upcoming hamfest, that may influence me; but that's just depends on what turns up - I know most of these will cost $$$ to ship, and putting one in my car to take home might (depending on the model or state of the equipment) save me some cash to do refurbishment with.  If I don't see one there (which is probably what will happen), online will be my next step and will give me many more options.  Appreciate the comments so far.

[pelule]

Just occured today at the German bay:
https://www.ebay.de/itm/HP3456A-Digital-Voltmeter-6-5-Stellen/283242734436?hash=item41f2952364:g:5fgAAOSwzINb3fNh:rk:3:pf:1
That's one of the newer (fan less) 3456A.
But shipment to the US may cost additional $100.
/PeLuLe

[GregDunn]

Excellent.  I'll keep watching if (as I rather expect) the hamfest comes up empty.  If I can't cart it home with me, I'm totally OK with reasonable packing/shipping charges - as long as the meter is in working condition and a fair deal to begin with.  I know how easily something that size could be wrecked in transit.  I also see units with $500-$800 prices PLUS hundreds of dollars for shipping, though; at those prices they should be working and freshly calibrated.   

[MLNL Laboratory]

The 3455A was sort of an orphan, really just the next generation past the long-lived 3450B but adding early processor technology to the mix.  The 3456A ended up being a lot more popular. 3456A's sell on Evilbay in the $80-125 range these days, and good working ones are worth every penny of that.

-MLNL-