Fluke 332D repair

[Rax]

In my thirst to accrue more reference at bench - metrological "agreement," anyone?... - and being lucky to live in Southern California (there's an orphaned instrument at every street corner), I got a 332D for very little money.

The only real issue with it being - the range indicator LEDs were kaput. Upon opening the unit - how interestingly packaged it is, with a hot, and insulated chassis, detachable window to make adjustments (insulated driver!), and a bunch of other quirky design decisions - the A5A6 module returns a toasty R3 (measuring just about 50ohms...). Out it goes, annd in goes a rugged 3.3kohm (closest I could find at 2W), though not WW as I like my rugged resistors. But it'll funnel about 17mA to these LEDs I'm fixing but a bit of a longer life (assuming vanilla 5mm red LED wants 20mA...).

Most of the work was mechanical. The LEDs I have - as most (all?) current production ones have a ridge on the bottom, which the mount for this unit wouldn't allow. I had to chisel the base a bit to remove that.

Pics enclosed. Nice to see this running happy!

[Rax]

Pics of the whole unit. How much brighter the current production LEDs are, even at a diminished current... (though I should really check that, innit?...  ).

[Rax]

one more pic

[Rax]

Word of warning - in these units (age, maker, etc.) I strongly feel all carbon comp resistors over 1W inclusively need to be replaced with stiff wirewound ones. They're not cheap, but the units deserve them in strides, and they'll last forever. Then there's obviously electrolytic caps that are well past their lifecycle. But I came to think the power carbon comp - which I feel should have never been a duty for them - are even more liable for catastrophic failures.

[Dr. Frank]

Congratulations, RAX!
Unit looks nice and seems to be one of the younger ones.
Does it work in all ranges?

I would be interested to see close ups of the reference board, the chopper board, and the pre regulator board, thank you!

Frank

[Rax]

Congratulations, RAX!
Unit looks nice and seems to be one of the younger ones.
Does it work in all ranges?

I would be interested to see close ups of the reference board, the chopper board, and the pre regulator board, thank you!

Frank

Thank you, Frank! I'll never get tired of the satisfaction of restoring an instrument (or anything vintage and electronic, really...)  Much more beautification left, including removing stickers, which I don't like to keep. In fact, I like to maintain this type of work at the same esthetic standards as my audiophile restorations (McIntosh, Fisher, HH Scott, etc.). Oops, I hope I didn't use no obscene language for this community!!... 

I don't see anything wrong with it this far (once the the LEDs were fixed). At 10V, it's somewhere around 8-6ppm off agreement with my P6048 (completely preliminary observations), though it's nowhere nearly as stable as my F5440A, from what I'm seeing. I could live with it, though, and it's a very clean, handsome, and very well built unit.

What's worrisome and I feel I need to address pretty quickly - to prevent actual damage to it should some of these fails before being preventatively replaced - is addressing the toasty 1W and 2W resistors, and then replace the not-so-toasty ones too.

[Rax]

The further good news is that one specific setting in a specific range (for instance, 10V in the 100V range as opposed to the same in the 10V range) is very consistent (apparently, to <1ppm,meaning the "single digit ppm" is repeatable, say, from day to day). If I cross between ranges for the same output, not so much. Not far off, but not quite the same. I need to do some diligent readings to say more specific things than that.

The bad news is that levels out over about 810V trips the 1000V protection setting. Hmm.   Not at all, just a bad case of RFM-tites... I haven't been paying attention to the vernier adjustment. Everything seems to work as designed.

[Rax]

I would be interested to see close ups of the reference board, the chopper board, and the pre regulator board, thank you!
Frank

Frank - I have some replacement resistors to be delivered before the weekend, and so I'll open the unit back up at the same time. Please do remind me if you find a chance this weekend to take some shots.

[Rax]

At 10V, it's somewhere around 8-6ppm off agreement with my P6048 (completely preliminary observations)

I'm seeing it drawing closer to agreement with the P6048 with more time passing (the "30 day bakeout?..." as bdunham7 put it artfully) and it's now pretty stable within relatively long integrations (20s is my default) at less than 5ppm off (@ around 27C). Please take with a grain of salt and read it as part of a repair and assessment of the condition of the unit.
______________________________
The next morning, at 25.7C, I am seeing at a very slivery 1.3ppm off... Not sure if it's an intersection of tempcos, or the positive result of a "bakeout..."

[Rax]

Well, maybe I shouldn't really be surprised. It's been hovering around the 10.0000000V on the P6048 for a while now. Typically +-.25ppm to maybe +-.5ppm off of the nominal 10V. Pretty mind blowing, and which I didn't really expect.

But again, if I dial in 10V on a different range, I'm nowhere near that kind of agreement. Which tells me the last adjustment of this instrument was primarily done at the 10V point on the 100V range. I welcome other thoughts.

Very, very, very satisfying. I've been in the restoration "business" (= invested hobby) for a good number of years now, and there's a lot to be said about "reforming" caps (by which I mean running the unit a generous amount of time to allow the wet caps - those not replaced, and most should, depending on age of unit ad other considerations - to regain their fitness), expelling moisture from units that sat around for a long time, etc. All units just want to be run with some frequency through their lifecycle to maintain good performance. There's no exception to this rule.

On the repair side - or maybe, long term service endurance - I receive parts to replace most power resistors today. It's just dutiful care for an exceptional instrument which, as they tend to, comfortably exceeds its spec. Another aspect I should mention is that, due to where I live (Southern California) I think I'm extremely lucky to run into very well cared for units. The incredible wealth of labs around here is amazing.

[Rax]

I would be interested to see close ups of the reference board, the chopper board, and the pre regulator board, thank you!
Frank

A5A1 - Reference Board

[Rax]

A5A4 - Chopper Amplifier

[Rax]

A7A2 - Pre Regulator

[Rax]

I would be interested to see close ups of the reference board, the chopper board, and the pre regulator board, thank you!
Frank

Frank - I'd be happy to send you a full higher resolution set by email.

[Rax]

One challenge I had with this is I did not quite realize how gentle I need to be when removing the external case. Due to the age, the plastic spacers that make sure the internal enclosure and the external case are kept isolated and distanced enough become very brittle. So I think I broke a couple, and some others were probably missing from before I got this, so I have to improvise and used furniture felt pads - they're insulating and adhesive, so I think they'll do OK.

Also, pay attention to the hatch that covers the adjustment controls - this needs to come off before the external case is slid off of the unit.

[Rax]

The other issue I mentioned is the "toasty" carbon comp >1W resistors.

Here's an example of one that was a time bomb (IMHO). Enclosed is a pic including R1 and R4 - same value, but apparently, different levels of stress on the two resistors. R1 was the time bomb.

Also depicted is the rehauled board.

[Dr. Frank]

RAX, thank you for the heads-up about the pictures.
So you still have the old reference with the KLIXON oven and the T.I. chip inside.. I thought that later versions already featured the SZA263 as well.
Anyhow, that all looks quite well, so have fun with that unit.
For the linearity calibration of the 7 digits, I recommend to use the 3458A you are to borrow.. just modify the alignment procedure accordingly.

Frank

[Rax]

So you still have the old reference with the KLIXON oven and the T.I. chip inside.. I thought that later versions already featured the SZA263 as well.
Frank

I can post the serial number if it helps document this. I don't know a lot about the 332's history and versions, but would love to get the data on it.