FLUKE 332B/AF in the slaughterhouse

[Dr. Frank]

I bought this instrument years ago "for parts".
The high voltage pre-regulator was totally blown, power semiconductors unobtainium.

I tested many stability and accuracy parameters in 10V and 100V range, by using an external PSU instead.

Now it's rip-off time, as you can see.
I will keep the precision assemblies for re-use, the rest goes to the scrap yard

This B/AF version had been assembled late 1972, when Apollo 17 flew to the moon.

So the cable harness is over 40 years old, and several cable isolation are awfully sticky.
Obviously, the plasticiser comes out of the PVC isolation.

The switching assembly, carrying the high voltage of up to 1200V, is isolated from the front plate.
That includes the metal case, and the switch shafts.

[krivx]

Have you contacted the volt-nuts mailing list? You may be able to part it out for a decent profit.

[Dr. Frank]

The B/AF version, and its schematics equals the 335D, only without differential VM.

It's a sophisticated version, all PCBs are fully equipped with semiconductors, i.e. no mechanical relay chopper.

On its 15V reference PCB, it features the very first reference amplifier, Fluke presumably invented, and which all of its later references and calibrators are based upon. (SZA263, LTFLU).

This reference assembly, the black round part, consists of an oven from Klixon. Klixon brand still exists, but terminated such temperature stabilizers recently.
 
The oven is a PTC - characteristics heater element, stabilizing the temperature to 76°C.
If the 24V oven supply voltage is kept constant to +/- 10mV, the oven temperature is held constant to a few mK.

The reference amplifier obviously is produced by T.I., P/N: DH80417B, date code 7223.
It is put upside down into the oven part, and then the plastic cap fixes the whole assembly, P/N 4ST1-2 K2A.

The cap is quite thin, so the assembly is sensitive to air draught, several ten ppm fluctuation can be observed on the bench.
An additional poly styrene piece over the assembly improves stability greatly.

The reference amplifier is trimmed via Zener current to about +2ppm/K T.C. (without oven).

The 15V were stable after 3 minutes to 10ppm, and to < 1ppm after 6h warmup.

2h stability / noise is about 0.25ppm. (standard deviation)
That's at least 5 times worse than modern references, but exceptional for 1972, I think.

The instruments T.C. is specified 2ppm/K, ten times worse than later calibrators.

[Dr. Frank]

Here are the really good parts, I want to re-use.

The 332/335 can be understood as a big, inverting OpAmp.

The 15V reference creates 10µA, 100µA or 1mA constant currents by the trimmable, precision range resistors of 1.5M, 150k and 15k.

A chopper Op Amp with HV crowbar / driver stage produces the output voltage of up to 10V, 100V, or 1kV, determined by the sample string.
Very nice discrete chopper circuit, using 2 FETs already. 

The sample string is a 7 dial resistor chain, from 0.1 Ohm resistors on the lowest and 100k resistors on the highest dial.
That gives 1.111111MOhm max, 100 mOhm resolution.

Each of the first three stages of the sample string can be trimmed to < 1ppm linearity.

The range resistors and the complete sample string resistors are matched to the same T.C., so that the gain shift over temperature of the whole amplifier is very low.

See series numbers on the individual resistors, and the matching label "62" on both , range resistor and sample string PCBs. 

[Dr. Frank]

Well, I will just keep the reference and those two resistor PCBs.

Complemented with an LM399H assembly and a 7652 chopper they will make a handy 0..10V reference.

Adding my current source circuit (I have published here, elsewhere) will give an ultra stable constant current generator, adjustable to 7 digits resolution, and 6 ranges from 10.000000 µA to 1000.0000 mA.

Will be very similar to Krohn Hite CR 106 current source.

I think, the rest of that 332B is of no use for anybody.

Frank

[TerraHertz]

Oh, what a pity. I have a Fluke 332A, that's been sitting on a shelf non-functional for years due to a bad mechanical chopper. The contact points are tiny gold wires, and they'd worn enough to drift the sample phasing out of the required timing window, which meant no gain in the output voltage control loop.

With the chopper cover removed, it looked like it would be fixable by bending the contacts, but I couldn't figure out (in the time I had then) how to do it while observing the result, to get it right.

Still hoping to get that unit going again someday. While it worked it was very nice. I happened to be watching the output voltage on a HP 3456A DMM when it went bad, and seeing the previously highly accurate thing start to drift off was sad.

[Dr. Frank]

Oh, what a pity. I have a Fluke 332A, that's been sitting on a shelf non-functional for years due to a bad mechanical chopper. The contact points are tiny gold wires, and they'd worn enough to drift the sample phasing out of the required timing window, which meant no gain in the output voltage control loop.

With the chopper cover removed, it looked like it would be fixable by bending the contacts, but I couldn't figure out (in the time I had then) how to do it while observing the result, to get it right.

Still hoping to get that unit going again someday. While it worked it was very nice. I happened to be watching the output voltage on a HP 3456A DMM when it went bad, and seeing the previously highly accurate thing start to drift off was sad.

Yes, the 332/335 are quite nice.
The mechanical chopper can be replaced by a much better, modern circuit .. see here:

http://www.friedrich-messtechnik.de/cms/index.php?option=com_content&task=blogcategory&id=9&Itemid=14

Description is in German only, and just click on the photos, the explicit links do not work anymore.
That guy has tested the replacement, obviously. He also sells an LTZ1000 based, completely  ovenized 10V reference, which is traceable to our German PTB.. so he seems to be a metrology wizard... 

His chopper replacement should even be better than the original Fluke FET chopper, I have shown here.

If you can redo the layout (without those bugs), and etch the PCB, that would revive your calibrator.

Frank

[Vgkid]

Thanks for the post Dr. Frank.

[TerraHertz]

Yes, the 332/335 are quite nice.
The mechanical chopper can be replaced by a much better, modern circuit .. see here:

http://www.friedrich-messtechnik.de/cms/index.php?option=com_content&task=blogcategory&id=9&Itemid=14

Description is in German only, and just click on the photos, the explicit links do not work anymore.

Thanks, interesting! Via google-translate the text is clear, and I've screen-cap'd the illustrations. (Why do people do that 'you can't save-as my pics' thing?)

His chopper replacement should even be better than the original Fluke FET chopper, I have shown here.
If you can redo the layout (without those bugs), and etch the PCB, that would revive your calibrator.

For simple, one-off circuits like that, kynar point-to-point wiring on fiberglass perf-board is easy and works fine. The one construction problem is the weird board connector. I don't want to cut up the existing board, but if I can find another with the same connector I can cut and graft the entire thing to some perf-board.

Another nuisance is that in my unit the 'included' card extender is missing. So are the internal top and bottom shield plates, but they are easy to make - just flat sheets of aluminum with some holes.
I bought it on ebay years ago, cheap as it was listed as dead. Problem was a bad electro, easily fixed. But whoever had previously tried to fix it was a bastard, and had not bothered to replace the internal covers and extender.

I have an original manual with schematic, so this upgrade idea is very attractive.

Pics:

[TerraHertz]

Hmm... So you are not going to keep the chopper PCB?
It looks like it has the exact same edge connector mechanicals as my 332A chopper board.
I wonder if it's actually electrically compatible?
See pic of my dead one, with the schematic.

At the worst case, I could use the edge of the card with the contacts, together with the circuit from that site.

Do you feel like selling it? Or better still, donating it? I'd pay postage.

Edit: I just noticed the card # is '404'. How ironic.

[Dr. Frank]

Hmm... So you are not going to keep the chopper PCB?
It looks like it has the exact same edge connector mechanicals as my 332A chopper board.
I wonder if it's actually electrically compatible?
See pic of my dead one, with the schematic.

At the worst case, I could use the edge of the card with the contacts, together with the circuit from that site.

Do you feel like selling it? Or better still, donating it? I'd pay postage.

Edit: I just noticed the card # is '404'. How ironic.

It seems, sending that PCB to Australia would not be that expensive and not complicated.. dunno about customs declaration.

The chopper should be a plug-in replacement, I assume... will verify that.. perhaps those three zero trimmers have to be adapted.

As your 332A has those just beautiful drum dials, it would be a pity not to make a transplant...

Frank

[TerraHertz]

It seems, sending that PCB to Australia would not be that expensive and not complicated.. dunno about customs declaration.

The last thing I bought from Germany was a manual, and that was no problem. I'll happily pay for a pack and post. Customs - usually post offices have small stick-on declarations. "Vintage circuit board" or something like that. I'll PM you my postal address and email.

The chopper should be a plug-in replacement, I assume... will verify that.. perhaps those three zero trimmers have to be adapted.

I found a 332B manual here: http://www.liberatedmanuals.com/TM-9-4931-383-14-1.pdf   (21MB)
A quick compare of the chopper amplifier in that to my 332A schematic (see scan) - they possibly are pin compatible.
The 332B manual also includes a mechanical chopper the same as my board - looks like it's an option.

As your 332A has those just beautiful drum dials, it would be a pity not to make a transplant...

It's certainly a stroke of luck for me!

Yes, I really love those clunky but pretty controls.

[CaptnYellowShirt]

Thanks for the great write up and pictures! 

[SoundTech-LG]

The 332B/AF must be a bit later version of the 341A/343A. Very similar circuitry. The voltage ref. ckt. using an op amp, where the 341A/341B Vref uses discretes. Interesting to see the development changes. My 341A had a bad 2N3904 in the vref ckt., all cal'd up and running fine now.

[guido]

Hi all!

My first post here! I've been watching Dave's videos and reading the forum for a while now. When i saw this post, i registered and contacted Frank to see if i could get a connector set. I've got a 335D with a bad null meter and i would like to make myself an extender card. Instead of only the connectors, i've got all of the remains coming my way    I don't live close, but by a stroke of luck i've got a collegue that lives close in the Frankfurt area. I'll get it next week, after the carnaval holiday.

Here are some pictures of my 335D. In the voltmeter section, there is a transformer missing. This is present now after i got it from a scrapyard 335D from the states. But the nullmeter still doesn't work. When measuring V or I from the calibrator output, the meter is fine. The calibrator part itself also works fine, allthough i should check all of the parts.

So a big Thank You to Frank 

[Dr. Frank]

I just wanted to add the stability measurements, I have done on the Reference Amplifier assembly.

After turning on, the reference voltage shoots over, caused by a hysteresis effect in the RefAmp (not displayed here).

The assembly afterwards needs around 6h to stabilize to 1 ppm, see fig. 1.

Measuring the 2h stability between  25200 .. 32400 sec , yields 0.25 ppm of noise / instabilities (standard deviation).

The T.C. of the RefAmp can be determined  by fig. 2.

After switching off the oven at 76°C, the reference voltage decreases from 15.00015V to 14.99844V at 21°C, giving around 2ppm/K T.C. of the non heated RefAmp.
 

[Dr. Frank]

In the last part, I'd like to show the overall stability of the 332B/AF versus the HP3458A.

After 12h of warmup, and with ambient temperature stable to +/- 0.3°C, the 10V output from the 332B/AF is stable to +4 .. -2ppm.
Many disturbances can be observed, their root cause is not obvious.

The 2h stability/noise, measured between 39600 and 45800 sec, yields around 0.43ppm (standard deviation).

The successor, Fluke 5440B/5442A is about 10 times more stable and less noisy, i.e. 0.04ppm stdev over 2h.
(That's also a reason, why I tore this 332B apart)

Here's an updated list of reference sources, DVM and calibrators, regarding their stabilities and their known oven temperatures.
The Fluke 8508A should be built similar to the Datron 1281.

The only device, which oven temperature is not exactly known yet, is Keithley 2002.
I hope, TiN is able to measure the temperature on his device soon.

Frank

[classicTEK]

Does anyone have the full size images from the german website and the chopper?

Cheers,

David

[guido]

pm sent 

[guido]

So i made the extender with connectors from the parts from Frank's 332B:



Trying to fix the null detector metering:



I replaced some parts (bad cap) and tried to get it working. But the meter would go all over the place when used as volt or diff meter. Only monitoring the 335 V and I worked fine. Probed and tested a lot of parts, no luck. Put it aside a few times (a 2465 came along  ) and tonight i gave it another try. So i fiddled a bit again (taking out some components to test them) and got it working. Great, put it all back together and..... bad again. 

Then i finally got a bright idea and had a close look at the connectors on the pcb. And sure enough, one of them had two bad soldering joints, just noticable. Turnes out to be the one (16) for the connection to the sensitivity switch/resistors in the feedback loop of the amp 

So next is a good clean of the two pcb's i had my hands on and then check against my meters. It probably needs some tweaking. The voltage trip doesn't seem to work in the 10V range, but i probably won't bother.

The remains of the 332 now live in a shoe-box 

[casinada]

I have a Fluke 3330B sitting under my desk I got not working (from ebay). Finally I opened it over the weekend and found a blown resistor (R1=68 ohm 2w) on the preregulator board and a few flaky capacitors on some of the boards. It seems to be vintage 1982-1984, It doesn't produce any output voltage or current. The only voltage I measured internally is the test pins on the reference board = 10.000 (fluke 289).
It seems to be very difficult to work on this heavy unit without an extender board. Does anybody have some spares so I can make an extender board?
I would really appreciate and compensate anybody willing to help me
My chopper board is the newer vintage and all solid state. It was very hard to take the preregulator board out of the connector
Here are some pictures:

[TerraHertz]

I'd like to thank Dr.Frank for sending me the solid state comparator board, to replace my mechanical chopper based one that died in my 332A.

My unit had been working prior to the chopper failure, but it did have some other issues.
One was that when I'd bought it (ebay, 'unknown condition') it turned out to be missing the inner chassis top and bottom covers.

The 332A case is constructed with three independent layers of electrical shielding:
1. Outer metal case and front panel, at mains ground.
2. A 'guard' shield layer, brought out to a front panel banana post. This shield is constructed by lining the outer case with PCB fiberglass, with an inner copper layer that is made electrically contiguous via wires soldered between each plane.
3. The main internal chassis, which for some reason I don't understand, is connected to the '+' output rather than the minus.

The inner chassis is supposed to have top and bottom metal covers, electrostatically shielding the circuit boards from the Guard layer. But some bozo in the instrument's past before it came to me, had lost them.
Replacing them had the slight complication that they needed insulating spacers to keep the inner chassis separated from the Guard layer. Also the sheets needed were bigger than any of the scrap aluminium I had lying around.
I'd never got around to making replacements.

Now I had a new comparator board I decided I should fix up all the other little problems too.
Starting with making those shields. That's done now. A bit rough, but should work. For spacers I used some things intended for supporting glass table tops. The side spacers which are present are teflon I think, but I'm not sure if that's really necessary. The inner chassis can be up to 1100V above ground (scary machine to work on!) so maybe those spacers should be ultra low leakage? It remains to be seen if the clear PVC spacers I used are adequate. If not, they'll be easy to replace.

While visually checking out the other boards before trying to power it up, I noticed a very singed area on the 'current limiter' PCB, with the component that had overheated now replaced with a wire link. What?!

Took me ages to find that in the schematics, since the relationship between schematic sheets and boards is a bit random.  Turns out the front panel used to have filament bulbs for the decimal points, but at some stage a mod changed them to LEDs. This burned resistor was the current source for all the bulbs. Now the individual LED current limit resistors are in the wiring loom, hence the wire link on the board.

That's where I was up to when distracted by other chores. Still haven't powered it up with the new board.
Planning to make an extender board with the spare pins and socket Dr.Frank sent me, before doing more on the unit.

Edit to add: Incidentally the messy felt pen writing on the inner chassis is not mine. Perhaps by the guy that lost the covers. It's on the list to clean off and redo neatly.

[guido]

It seems to be very difficult to work on this heavy unit without an extender board. Does anybody have some spares so I can make an extender board?

I can send you one of Frank's 332B pcb's and a connector if you are willing to pay for the shipment (from europe).
Getting the individual pins of the pcb would be your job (was a bit difficult with the pcb i choose, but it might vary).
I could cut a part of the pcb to make a smaller package, but i don't think it matters much. Sent me a p.m.

The null meter went bad again yesterday. Ah well. Maybe i'll give it another go, but not now.

[BU508A]

Hello,

a few weeks ago I scored a Fluke 3330B on ebay. The seller said, that the switch on the
very left side for selecting the voltage/current does not work in position "8".
It turns out, that the switch is working perfectly well but the relay K3 on the A4A10
ladder driver no. 1 is hanging. I got the relay out, hooked it up to an external power
supply and after some on/off switching it was working again. Now the 3330B was able again
to select all voltages between 0 and 1111.111V. The current mode I did not check yet.

Then I set it to 1mV and checked with my 34401A and saw some dancing in the 10µV range.

I looked into the schematics and checked the voltage reference board. All voltages stood stand
still perfectly, so I checked the following chopper amplifier and differential amplifier.
On both boards were several electrolytic caps and one tantalum. I changed them all and the
dancing was gone, except for a +/- 1µV (the 3330B was working then for several hours).

To me this seems to be pretty good :-)

But this brings me to this: while fiddling with the cards in the 3330B I learned,
that there is something like an extender or riser board. But those boards seems to be
pretty hard to find, so I found this:

So i made the extender with connectors from the parts from Frank's 332B:

Does anybody know what's the name of these golden connectors (brand, name etc.) and probably where to buy?
I would like to build a riser board of my own, so that measuring will be much easier.

Every hint which may come will be helpful and really appreciated.

Thanks a lot.

Btw, I found also this very nice website with another 3330B repair attempt:
http://www.spurtikus.de/basteln/repair/fluke_3330b/index.html

The site is in german but the pictures are really nice.

[pelule]

I am also searching for that connectors to build my own extender card.

Got my Fluke 3330B in March last years for a really low price. I is meanwhile cleaned and now working pretty fine inside the specs after replacing some CAPs.
But I still have the plan to "pimp" it on the chopper (reduce short term drift) and reference (reduced long term drift).