Fluke 332D DC Voltage Standard Restoration

[TERRA Operative]

So I got me an old Fluke 332D.
Paid 10,000yen (about US$90) all up including shipping for it, and it was listed as kind of working but intermittently doing weird things with the output, something that screamed 'dirty contacts' to me seeing as this thing is full of rotary switches.

Got it home and it fired up fine. a bit scratchy on the dials here and there, so I spent some time on the lower dials with the deoxit and a light scrub with the fiberglass pen on the switch contacts and deoxit fader in the two pots. Still have to tackle the voltage selector switches.

The output is a little out, but I'll have to get my hands on an 8.5 digit multimeter to really dial it in, my best multimeter is a 6.5 digit Keysight 34461A.

I've also read that the caps in these tend to go bad, so I took inventory and made a full list on the Mouser website of caps to replace.
I won't be touching the tantalums as they are dry slug axial and are very reliable and generally fine unless obviously bad (and they are uber expensive to buy these days), but I did find all the 30D series electro caps to match perfectly (with only a little increase in rated voltage here and there). All the other standard electro caps will be replaced with Vishay axial, using the high temp and lower ESR versions where possible.

Also, what should be the Y caps on the input aren't marked with any specifications, so they will be replaced with new caps of the correct rating, along with a new mains cord so it's all shiny (The brass contacts are a bit tarnished and I have a limitless supply of mains cords).

The only thing I'm a little stuck on is the main filter capacitors.
They are 125uF, 450V Sprague caps, part number 106336 and have a really funky 5 pin footprint that no other modern caps use.
I don't know if they even need to be replaced, but if I do need to, I could either solder in some standard radial caps and just bend the leads a bit to match, or make a secondary board to piggy-back the new caps on and use jumper wires to attach it to the main PCB.

Last pic is of this type of cap.
Any thoughts?

[tggzzz]

The only thing I'm a little stuck on is the main filter capacitors.
They are 125uF, 450V Sprague caps, part number 106336 and have a really funky 5 pin footprint that no other modern caps use.
I don't know if they even need to be replaced, but if I do need to, I could either solder in some standard radial caps and just bend the leads a bit to match, or make a secondary board to piggy-back the new caps on and use jumper wires to attach it to the main PCB.

Last pic is of this type of cap.
Any thoughts?

They can be awkward to remove; care is required,

The best way is to make a secondary PCB for the new caps. One technique to avoid jumper wires is to

• measure the width of the existing lugs and diameter of holes in the existing PCB
• on the secondary PCB, put two holes slightly smaller than that distance apart
• solder a bog-standard 0.1" header into the two holes, then insert the two headers into one of the PCB holes, and solder

Ensure gaps between tracks on the secondary PCB are sufficient to avoid HV breakdown!

[Edwin G. Pettis]

I have the 332B and I had to go through and replace virtually all of the caps, many had leaked.  Those large Sprague caps can be replaced with newer radial caps but be aware that (at least in the B model) they used the cans as part of the interconnect circuits, you will have to put shorts in place of the cans or you will have open circuits.  Not difficult to see where to put the wire shorts in on the PCB.  No modifications to the PCB were needed.

[TERRA Operative]

Yeah I thought that might be a thing to watch for, but I just took a look and it seems like I'm safe, they aren't using the case of the cap as an interconnect on this one.

One thing I'll have to figure out is how I'll fix an adapter board in place so it doesn't stress the PCB etc.
I think I'll have to squint at it intently for a bit and maybe frown a little too until I come up with an idea.

The problem is, it's so clean inside that I want to try to keep it looking as untouched as possible.


Maayybbeee I could restuff those caps, but maybe I can't be bothered..... hmmm.

[bitseeker]

Yeah, apart from the bit of corrosion on the controls, it's immaculate inside. Nice find, TO.

[TERRA Operative]

Ok, I think I have a plan for those big capacitors.

I think I'll use something like this to restuff them: https://www.mouser.jp/ProductDetail/871-B43547A5157M000
I'll 3D print some spacer rings to hold the new capacitor inside the shell of the old too, then wire the new capacitor to the old capacitor pins, matching their original footprint configuration.
Then I'll put a little label on the top with the details of the change, and reuse the cardboard insulator tube thingos as fitted from factory to make it all look original.

I think it's the easiest way to mount the new caps, and will look completely original too.

[TERRA Operative]

So, got all the capacitors ordered from Mouser, not so cheap those axial caps....    I'd have saved a few bucks if they were radial, but it is what it is...

Also, I started cutting the big PSU caps open to stuff the new caps inside when they arrive and found the blade in my pipe cutter is completely blunt and chewed up somehow. I can't remember what I would have cut to make it so bad but I'll have a new blade soon.

[Zucca]

Love it, congratulations TERRA!

[TERRA Operative]

Gots me a new blade for the pipe cutter and cut open the caps, made a good job of it too.

Now I just gotta get my 3D printer online and start printing the 3 sabots to hold the new caps centrally inside.

[drknob]

Check this source: https://hayseedhamfest.com/
They'll do custom caps.

[TERRA Operative]

I replaced all the capacitors in the unit now, pretty painless with all the removable cards, I didn't even have to remove the HV motherboard to replace the caps there either.


I ended up gutting the old big PSU filter caps and 3D printing a sabot to hold the new ones centrally inside.
They slip in just nice and with a little bit of aluminium tape to seal the cans back up and a label on top, they'll work nicely I think.

[Zucca]

and you didn't fire up the beast? 

[TERRA Operative]

Gotta keep you guys wanting more!

Actually, I had to go to work, but I will fire it up real soon.

[TERRA Operative]

Ok, so I'm starting to play around with tweaking dials and getting this thing working right and I have realised that the extender board is missing....
Looks like I need the PCB pins and an edge connector which are both obsolete... yay..

Does anyone have a 332(x) parts unit they can sell me some bits from by chance?


I found this info, but it'll be a long shot to find anything on the ebay/etc....
Details of part numbers:
https://www.eevblog.com/forum/testgear/fluke-332baf-in-the-slaughterhouse/msg761177/#msg761177

Pic of a home-made extender card, showing the pins and edge connector:
https://www.eevblog.com/forum/testgear/fluke-332baf-in-the-slaughterhouse/msg445755/#msg445755



I also found this which looks interesting...:
https://www.eevblog.com/forum/testgear/fluke-332a-adjustmentverification/msg685631/#msg685631

[TERRA Operative]

Alrighty, got all the capacitors replaced and no output.... 

After some poking around, I found a bunch of out of spec carbon composite resistors inside and a busted Zener on the Aux PSU board. It's the precision 6.3V one in position CR6. I'll replace it with a 1N4735 zener for testing then swap to a super low temp coefficient 1N829A once it's working.

I think I'll rip out all the carbon composite resistors and replace them all with metal film resistors too (I can get Japanese 1% tolerance, 50ppm metal film resistors for a good price).
I figure if some are bad (6 out of 14 are bad on the Aux PSU board alone), I may as well replace them all to be sure they are all good so I don't end up chasing my tail then replacing them later anyway.

The resistance checks in the service manual at the start of the troubleshooting section indicate there is a problem with the Aux PSU board, so replacing these bits might just get it working enough to test the rest of the unit...



Also, I am restoring and upgrading my variac to allow me to test stuff more easily. Prompted by the need to use one for some of the tests on this 332D.
It got a full disassembly, a sandblast and repaint in hammer finish paint, then a 3D printed box with a good amount of plugs and sockets to make it's use much easier than the old basic binding posts that were on it.
Just sent an email off to the manufacturer to see if I can get new handles and a dial faceplate. Fingers crossed as I had luck a while back sourcing spare carbon brushes from them.



Next step is to hit Akihabara tomorrow for resistors and diodes, then it's time to give the desoldering gun a good workout. 

[TERRA Operative]

Well, I'm going to have to have a sit down chat with my 2 year old son.... I caught him poking around in the 332D and after telling him 'no!' and giving him a Tek scope to tweak dials on instead, I didn't think much more of it.

Turns out he broke a wire on the power switch..... 
No big deal in the end, it was a quick repair.
I wish I saw it before I started replacing resistors though, I planned on testing the unit before and after and assumed I tweaked something during the capacitor replacement, so went ahead replacing ALL the things! to eliminate as much as possible. I didn't count on a simple broken wire.... 

So now I have almost all the carbon composite resistors replaced, just a few to go.
It turns out at least a third are out of spec, so not a complete waste of time...
I just have to source two more. The store in Akihabara didn't have a 2.7\$\Omega\$ 1/2W resistor in the type I wanted, and no-one seems to make a 1.1\$\Omega\$ resistor in the specs I want too. Digikey only list them in 5% tolerance 350ppm or so.

I'll probably stick a much more common 1.2\$\Omega\$ resistor in, unless someone tells me it's a bad idea?....
The resistor in question is R20 to the far center-right of the first schematic shown below, feeding into the second schematic.

[tggzzz]

Well, I'm going to have to have a sit down chat with my 2 year old son.... I caught him poking around in the 332D and after telling him 'no!' and giving him a Tek scope to tweak dials on instead, I didn't think much more of it.

I used two techniques to teach my daughter that electricity can bite.

The first was to give her a "lightning strike" from an old piezoelectric Zerostat used to dissipate dust-attracting static electricity from vinyl LPs.

The second was to have her touch an electric fence. Before doing that I made sure she knew to touch it with the back of her hand so there was no chance muscles would contract and grip it. I also demonstrated how to do it.

In her early teens, we backpacked around India without knowing where we were going to sleep at night, and before driving a car she was making forced landings as a solo pilot.

In other words, I showed her how to recognise danger and avoid the consequences.

[TERRA Operative]

Yep, I'm making sure he plays safe. He knows his boundaries, he just likes to push them.
No access to energized equipment of any type though, he's gotta be older for that. For now he just pushes buttons and turns dials and sometimes doesn't break stuff.

[tggzzz]

Yep, I'm making sure he plays safe. He knows his boundaries, he just likes to push them.
No access to energized equipment of any type though, he's gotta be older for that. For now he just pushes buttons and turns dials and sometimes doesn't break stuff.

You want to encourage safe exploration; you will never ever get the balance completely right!

It does no harm for him to realise that safety boundaries are there for good reasons, and that violating them can have unpleasant consequences.

Early teens is a good time for people to read Tom Godwin's classic short story "The Cold Equations", https://photos.state.gov/libraries/hochiminh/646441/vantt/The%20Cold%20Equations.pdf

[TERRA Operative]

Alright, this one has fermented on the to-do pile long enough, so time to get back into it.

All carbon resistors and capacitors are replaced, so that's looking good now.

My next problem is that the service manual is a little self-referential in that I apparently need another one of these units to properly test/calibrate this unit..... hmm.
Also, I apparently need a differential voltmeter, anyone know if my Keysight 34461A 6-1/2 digit multimeter is a good enough replacement, or should I look at getting a proper differential voltmeter? (which means a whole nother project too....  )

So next step is to run it through the tests in the service manual as far as I can with the gear I have here to see how it looks and see what dials I have to tweak. I had better get my lucky socks out and practice holding my tongue in just the right position.

[Dr. Frank]

Hello,
all linearity calibration, and also the range calibrations are done by differential method, which is not necessary, if you get access to a higher precision DMM, like 3458A, 8508A, or so. Therefore, Null Detector is also not necessary. The 34461A anhow would be ok as a Null detector in the standard setup, instead of the 845AR, but not for the 1kV range, as that would exceed the common mode voltage limit.

The linearity calibration requires a DMM with at least 0.1ppm linearity, that is 1µV on 10V scale, so your 34461A with 2ppm linearity is not enough.

The absolute calibration for 10, 100V and 1kV can be done in good precision with these mentioned 8.5 digit DMMs directly, but the 3458A has a very bad 1kV spec., so you would need another one, or a 752A.

Frank

[TERRA Operative]

Hmmmmm, I'll have to track down a better meter somewhere.
I might just do my best with the 34461A to at least see if I can get it in the ballpark (With all the replacements I've done, it's not like I'll make it worse than it is now...) and if it checks out, then I can find a better meter to give it a real adjustment.

[valley001]

It is good to see you have not given up hope on this. 

I have been working with my 332D for some time, and I believe I tracked most of its issues.  The most recent problem was intermittent failure of the chopper (solid state version) to function correctly.  It would work and then quit, with the voltage output becoming screwy.  In an attempt to readjust the chopper (per 4-65 in the manual) barely touching R43 would result in the output suddenly becoming stable.  I guess that pot is on its way out perhaps.

When working I can get 1.000000 volt output within a few counts on my 3456A (dithers between 1.000001 and .999999), which is still a bit out of spec if my understanding of the manual is correct. 

[Dr. Frank]

When working I can get 1.000000 volt output within a few counts on my 3456A (dithers between 1.000001 and .999999), which is still a bit out of spec if my understanding of the manual is correct.

Which manual do you mean, that of the 3456A, or the 332D ?

The Fluke 332D specification indicates 10 ppm setting + 10µV for the 10V range, plus 20µV_rms of noise,  therefore your observed +/- 1µV is unbelievably better than that. The 3456A specification might even be worse, 8ppm @ 24h, 23ppm @ 90d,  so everything is well inside any spec, I think.

Frank

[valley001]

Hello Dr. Frank,

I was referring to the 332D manual but I still do not fully comprehend how these specifications work in terms of output accuracy vs stability,  I need to study them more.  Are you saying that at 1.000000 setting one could observe fluctuation of 1.000005-.999995 and that would be in spec for the 332D? 

I have not calibrated my unit I am simply running it and observing how stable the output is over a period of time.  My 3456A is in calibration and after warm up I can set the dials on the 332D to achieve a 1.000000 volt output (1.000001-.999999 observed) but I have to set the 332D at .999876 or so on my un calibrated 332D.   I do not have access to a 8.5 digit meter for calibration. 

When working I can get 1.000000 volt output within a few counts on my 3456A (dithers between 1.000001 and .999999), which is still a bit out of spec if my understanding of the manual is correct.

Which manual do you mean, that of the 3456A, or the 332D ?

The Fluke 332D specification indicates 10 ppm setting + 10µV for the 10V range, plus 20µV_rms of noise,  therefore your observed +/- 1µV is unbelievably better than that. The 3456A specification might even be worse, 8ppm @ 24h, 23ppm @ 90d,  so everything is well inside any spec, I think.

Frank