Fluke 382A Voltage/Current Calibrator Repair

[timb]

Last week I picked up a “non-working” Fluke 382A Voltage/Current Calibrator for a decent price on eBay. Once it arrived and I nearly broke my back getting it unpacked and upstairs, I plugged it in to see just how non-working it really was. The meter pegs off the scale and I get 120VDC on the output. Yup, she’s broken! So, I picked up the service manual from Artek and started debugging.

Specifications (Service Manual)



(Sorry for the lesser quality on some of these pictures; this thing is so big I can’t fit it on my bench, so it’s resting on a bed in the guest room where the lighting is shit.)

Factory Calibration Sticker


Front Panel


Top


Details Inside




Rear (Back Panel Flipped Up)


Bottom

[timb]

So, I started out by going through the troubleshooting tables in the manual. For loss of regulation, they recommend checking R723 on the Main Amplifier board. According to the parts list, that should be a 100 Ohm 1/2W resistor. Measuring what was on the board came out to about 5.7K! Ahah, there’s my problem, right? I soldered on a 100R, popped the card back in, flipped it on and… POP!

The resistor literally exploded. At this point I looked at the banding on the resistor I took off…4.7K! WTF? So, the schematic and parts list is clearly not correct. I found a picture of another amp board on eBay with a 2.2K R723, so I’m not sure what’s going on there. I did try a large wattage 2.2K I had, but it starts overheating after a few seconds.

So I’m putting the original resistor back in for now so I can start measuring some voltage rails.

[tautech]

Looks like a beautiful thing. 
Good luck with her.
Keep the photos coming.
Can you post some specs in the OP?

[timb]

Looks like a beautiful thing. 
Good luck with her.
Keep the photos coming.
Can you post some specs in the OP?

Thanks! Specs added to the OP as requested. One thing I love about this is the modular form factor. The cards literally pop right out. Apparently the unit originally included some sort of adapter that let you run the cards outside of the unit for troubleshooting purposes. I wish I could find one, but I may end up having to make a board up that lets me extend all the connections to another board with that style edge connector on it.

[timb]

The ovenized current and voltage reference card:



The DC-AC Chopper card; look at that huge can:

[tautech]

Looks like a beautiful thing. 
Good luck with her.
Keep the photos coming.
Can you post some specs in the OP?

Thanks! Specs added to the OP as requested. One thing I love about this is the modular form factor. The cards literally pop right out. Apparently the unit originally included some sort of adapter that let you run the cards outside of the unit for troubleshooting purposes. I wish I could find one, but I may end up having to make a board up that lets me extend all the connections to another board with that style edge connector on it.

Simple enough to etch a strip of PCB to match the edge connector, but sometimes finding the matching socket can be a problem. IME on older stuff they are 0.1 or 0.150 inch pitch.
Get as wide as you can and cut to width, pull un-needed connectors etc.
PC IDE ribbon cable is great for connection if the voltages are not excessive.

[timb]

Yeah, matching the socket will be the challenge. I had a look around Digikey and can't find anything with that matches. So I'll either do like you said and get wider, or simply take the contacts out of an old ISA socket and solder them down with the correct spacing to two boards, which I can bolt together using some plastic as spacers, effectively creating my own ghetto socket. (I've done this before, works great!)

In other news, I found an entire set of boards from a working pull for $30 on eBay! Of course I bought them; at worst I'll have a nice supply of spare parts, as I plan on fully restoring this to original condition and keeping it as a transfer standard.

I found a label on the side showing the original factory calibration:



This thing is 5 months (to the day) older than I am!

Here's a picture with the back panel open, showing the rectifier assembly (black cage in the center) and SCR relay (center right), main pass element (far right, large heatsink) and finally, several resistors with a small lightbulb underneath [which I assume is to heat them] (far left):



Then we have a view from the bottom of the unit, look at that huge ass transformer in the center (which has to weigh at least 30 of the total 50lbs of the unit):



That loomed wiring is really a work of art. (That's one reason I've been restoring old Power Designs supplies lately; so much great craftsmanship went into these older bits of test gear.)

Sent from my Smartphone

[timb]

So, that set of "working pull" cards from eBay got in yesterday...



They all looked good, until I got to the most important card of all, the Main Reference. Looks like something very, very bad happened to a resistor next to the oven. *Sighs* Working pull my ass!











Hopefully the oven card from my unit isn't the problem; I'll install these today and see what happens!


Sent from my Smartphone

[rastro]

Really great pictures.  The unit looks in excellent shape - nice catch.

[PaulAm]

These are great pieces of gear.  I picked up a 332B described as not working and the only problem was the voltage limit control was turned all the way counterclockwise to trip at a very low voltage.  Mine had the extender included.   You can find NOS connectors on ebay for cheap if you look for a while.

I have a translation of a German page, I think, for a chopper board replacement.

[SeanB]

On that board go hunt the shorted tantalum cap...........

[timb]

On that board go hunt the shorted tantalum cap...........

Ding ding ding! C102 is shorted like Gary Coleman with no legs!

Found it this morning after mulling over the schematics.

Still haven't had a chance to plug the new set of boards (sans Main Ref, still not sure of the extent of damage on it) in yet.

I need to verify all the transformer tap voltages with no boards installed first, to make sure I don't blow this new set of cards.

I'm also waiting for a set of neon bulbs to come in, but I'm not sure how critical they are? (They're wired in series across the transformer secondary, to protect the SCR according to the manual.)


Sent from my Smartphone

[timb]

These are great pieces of gear.  I picked up a 332B described as not working and the only problem was the voltage limit control was turned all the way counterclockwise to trip at a very low voltage.  Mine had the extender included.   You can find NOS connectors on ebay for cheap if you look for a while.

I have a translation of a German page, I think, for a chopper board replacement.

Interesting, I'll keep an eye out on eBay for that connector.

Have a link to that German translation? Sounds neat! (This chopper board produces a very audible 60Hz hum.)


Sent from my Smartphone

[PaulAm]

OK, I dug around and I originally ran across the link in a thread right here on eevblog.  Here's the thread with the link to Friedrich Metrology:
     https://www.eevblog.com/forum/testgear/fluke-332baf-in-the-slaughterhouse/
Thanks to Dr Frank for that link

The page is in German, but Google translate does a pretty fair job.