Data Precision 8200 calibrator - repair and other fun stuff

[Rax]

Hi all,
I was very lucky to score one of these calibrators during the slow days of holidays - I'm more convinced every year that's a very good time to be combing through listings and get good deals - and, as they seem to typically need, the only real issue was a complete restoration of the switches. All of these seem to look like they've been immersed for years in households of heavy smokers or something, as the grime on those switches is just incredible.

Enclosed pics depict some of this work, though not the perfect cleanliness of the finished product after I switched to using an eraser. I simply forgot that I used to do this (I even have an electric eraser and a full set of tips...) - I guess sometimes one forgets their own figured out methods. In any case, with the eraser, the circular concentric lines are gone too and the tin surface is perfectly clean and shiny. I used IPA and ammonia alternatively to clean this, before the eraser, with a good wash of IPA wrapping it up every time, so if there's anything left from the eraser, it'd be removed.

I'd be interested in hearing some overall thoughts on this calibrator. My units are up to 6.5 digits, so this seems to be perfectly adequate. This far, everything I measured generated by this unit has been absolutely perfect to all digits (by instruments' agreement). I may bite the bullet, and, when everything is confirmed working, have this calibrated (meaning, verification) and tagged as such for high confidence provisions.

One thing I'm not really sure of is its 100mV output. I don't seem to measure it at the front terminals - but some sources seem to indicate that should only come out at the back. If that's the case, does anyone have some info how to achieve this? Is there some proprietary cable? I am not sure what needs to be connected to the "J301" and/or "J302" ports at the back of the unit.

Thank you for your input in advance.

[jwet]

Don't know what you paid but that's a great score- first class calibrator.  Basic spec is 10 ppm and 1 ppm/C drift which is 5 digits worst case.  You generally want a standard to be 10x of your DUT so you're probably shy of 6-1/2 digits technically.  I wouldn't hesitate to send it to a cal lab once you've got basic operation- see if they can give you actual readings rather than just running the standard cal.

The 100 mV output is indeed only available on the back.  Its kind of an unbuffered output vs the front panel kelvin 4 wire stuff- two wire only and 100 ohm output Z.  Don't know why its done this way.

You might add some anticorrosion lubricant to the switches on reassembly- Boeshield T-9 or Deoxit D5.  Most common alcohols are 91 or 99% with the rest being water.

Have fun.

[Rax]

Don't know what you paid but that's a great score- first class calibrator.  Basic spec is 10 ppm and 1 ppm/C drift which is 5 digits worst case.  You generally want a standard to be 10x of your DUT so you're probably shy of 6-1/2 digits technically.  I wouldn't hesitate to send it to a cal lab once you've got basic operation- see if they can give you actual readings rather than just running the standard cal.

The 100 mV output is indeed only available on the back.  Its kind of an unbuffered output vs the front panel kelvin 4 wire stuff- two wire only and 100 ohm output Z.  Don't know why its done this way.

You might add some anticorrosion lubricant to the switches on reassembly- Boeshield T-9 or Deoxit D5.  Most common alcohols are 91 or 99% with the rest being water.

Have fun.

Thank you, jwet.

I actually forgot to mention that I did indeed recondition the contacts with Deoxit. To do that, I used cotton swabs just to keep the Deoxit on the metal surface only. The switches work great now (I still have to do the +/0/- and the range... which are working fairly OK but I can't resist!).

[Conrad Hoffman]

It's a great unit. Those switches are the weak point and I didn't know you could get them apart for cleaning. Mine are terrible and no amount of soaking or Deoxit has gotten them back to reliable. Still, whatever the display says, is correct, even if you have to fiddle the switches a bit to get there. The reference is a LM399. I suspect a cal house would charge an arm and leg to properly calibrate it, as all the (clever) octal? ranges need to be adjusted. You'd be way better off to find a good KVD and reference, and do it yourself. Does yours have the HV or GPIB options?

[Rax]

It's a great unit. Those switches are the weak point and I didn't know you could get them apart for cleaning. Mine are terrible and no amount of soaking or Deoxit has gotten them back to reliable. Still, whatever the display says, is correct, even if you have to fiddle the switches a bit to get there. The reference is a LM399. I suspect a cal house would charge an arm and leg to properly calibrate it, as all the (clever) octal? ranges need to be adjusted. You'd be way better off to find a good KVD and reference, and do it yourself. Does yours have the HV or GPIB options?

I highly recommend doing the switches - not a difficult job and shouldn't take long (there are some youtube videos on this). Getting to them is pretty straight forward and even the switches are pretty clearly intended to offer the possibility of servicing (which, really, applies to the entire unit). Once done, all switches will operate flawlessly and done with care - for instance, I've obstructed the adjustment holes through the shielding inside to protect the reference circuitry during the work - nothing else should be disturbed.

I'd probably just have a cal house check their performance, not adjust them - I am in Southern California and, with all the wealth of them around, I am not aware of any here willing to adjust something like this. But checking and possibly providing long form data paperwork for not much $ is possible. As the unit seems to close or dead on, I think I'd be willing to risk it.

That said, if anyone in this community is near me and would have what it takes to adjust this to calibrated state, please do let me know.

[Rax]

Does yours have the HV or GPIB options?

The sticker in the back is a bit hard to read, but it seems to say the "100V" and "HV1" options are present. That said, I am getting 100V out of this, but not HV (as expected if that board's not in, I see "Error" on the display if I switch to the corresponding mode). GPIB option is present.

[Conrad Hoffman]

Yes, mine has 100V but no 1000 and no GPIB. Note this was sold as Data Precision 8200 and also Analogic AN3200 (mine). Not sure if there are any significant differences.

[Rax]

You'd be way better off to find a good KVD and reference, and do it yourself.

So, is a preferred adjustment method for a unit like this? It seems to be what the SM indicates. I am unsure what the possibilities are in my neck of the woods - whether it's more likely to find a high end reference AND a KVD, or other options (?). Still looking for anyone with the right equipment (high end voltage standard, KVD, 8.5 digit calibrated DMM, etc.) in Southern California to assist with this, but hopeful some options will emerge.

[Conrad Hoffman]

Anybody with an 8.5 digit meter can set this up. The problem is it's the sort of manual thing that cal labs do less and less of, and probably charge more and more for. Certainly call around and get some quotes. My experience with a sample of one is that the unit handily beats its specs over quite a few years. It's old, so things have drifted and settled about as much as they're going to.

[Rax]

Anybody with an 8.5 digit meter can set this up. The problem is it's the sort of manual thing that cal labs do less and less of, and probably charge more and more for. Certainly call around and get some quotes. My experience with a sample of one is that the unit handily beats its specs over quite a few years. It's old, so things have drifted and settled about as much as they're going to.

I've called around last year - maybe I'll give it another shot now - but I was unable to find even one facility willing to calibrate AND adjust an older unit such as this. They're willing to take it through verification, but not adjustment. If anyone's in my neck of the woods and knows differently, please pitch in.
My current solution is to have it adjusted as close as possible within a community member's bench, and then possibly bite the bullet and have it verified and hopefully stickered.
And so I just had my ol' 8502A gone through this treatment - you know who you are! And thank you!! - and it seems to be very, very close (or dead on in some ranges and values, such as 10.00000V) - to the 8200. Which confirms both the quality of the treatment and the excellent condition of the 8200. Though I still have to verify the 100mV is present at the back.

[branadic]

Sorry for highjacking the thread.
I eventually received a Data Precision 8200 branded as Analogic AN3200. Overall, the unit is in good shape and working. However, it needed a bit of a clean and adjustment to bring it back into spec.
The encoder disks of the conductive encoders were slightly tarnished but some polishing and bending of the fingers brought them back to operation. Different to videos on YT



the metal plates that hold the encoder together don't have the notches that are bend over, but rather have a dent to hold them in place.

The unit has the LM299 installed. It comes with the GPIB interface, is missing the 1000 V option, but doesn't throw out an error when the switch is set to the 1000 V position. Also, the unit resets the voltage setting if the polarity switch is changed in position, which is a bit unfamiliar to work with.

It won't win a design award and is rather ugly looking to be honest. However, it works a treat.
So the question arises, can it be improved (noisewise) by some component upgrades? The 20 bit DAC is pretty simplistic and there are some circuit design choices that I would have probably done different. One of which is, the reference voltage is divided first to be then amplified again, but also the way the divider and its adjustment is implemented.
Upgrading the unit with a lower noise ADR1399 would also require replacing Z6 (AD517, TO99 package). The lower noise OP(A)27 comes into mind. This however also requires adjustment of R7/R8/R9/R10/R12. Replacing Z14-Z19 would probably be a good idea too, to decrease noise. Are there other suggestions?

http://www.ko4bb.com/manuals/2.205.134.124/8200_20_BIT_DAC_A1_PN_60-1090_REV_0AD_Schematic.jpg

-branadic-

[Kleinstein]

The OP27 would not be a good replacement for most of the OP-amps: with the higher speed there is a chance it would oscillate. A more suitable replacement would be more like OP177 and similar low bias precision OP-amps of comparable speed.
Even for Z, some 5 K input impedance are a bit on the high side for an OP27 with little advantage over an OP07.
For the overall noise Z14 and Z19 also contribute comparable (depending on the DAC setting more or less).

The capacitor C19 likely has to go with a new OP-amp for Z6.
The ADR1399 of cause needs the RC for damping.
If the voltage is not too different, one may get away with the same old R8.

The system with divide first and than using a tap of the precision resistor chain is not that bad. The extra divider has not that much effect (only goes from some 7 V to 6 v)  and the resistor chain for the gain is anyway there for the DAC.

I don't see decoupling capacitors for the 4051 and 4094. One could consider to add some and a few ohm series resistor to the emitter of Q11.

For the current shunts / resistors one could think about adding some protection - though this may not be easy.

The question is if a new ADR1399 is really that much better than a well aged LM299. It would be lower noise, but likely more drift for at least the first few years.

[JK21]

I have a DP8200. Few mechanical repairs (a few screws and bolts) were needed. However, I have replaced the 100mV output connector on the rear panel.
I didn't like the original connector design, because the connections of the divider resistors were always bent when the connector was plugged in.
I used an XLR connector with gold-plated contacts and a small hand-made auxiliary board. The leads to the contacts are made with short strands and the divider resistors are no longer mechanically stressed.
This also improved the divider ratio from 100.0060 to 100.0011.

[Rax]

I have a DP8200. Few mechanical repairs (a few screws and bolts) were needed. However, I have replaced the 100mV output connector on the rear panel.

Can anyone provide some indication as to why this design choice? And also, what exact connector or dongle was being used there.

[JK21]

And also, what exact connector or dongle was being used there.

Sorry, I can't remember where and what exact type I ordered. There are various manufacturers of XLR audio connectors.

[Rax]

Sorry, I meant the original design choice. Ultimately, why route the 100mV range all the way to the back and on a J301 connector? Can this be efficiently rerouted to the main posts up front?
I have never even seen how a jack and/or dongle for that looks like.

[JK21]

I have never even seen how a jack and/or dongle for that looks like.

My first reason to swap the connector.

[Rax]

100mV range is now back online.

The range and polarity switches were not addressed at the first go at the switching assembly - as at the time they seemed to be mostly working OK. But upon later examination, I couldn't output proper levels on the back. After fixing the range switch, proper levels are now present at the rear output. Before this repair, I had some intermittent activity of the relays when using that switch, and I don't think the 100mV relays were ever properly actuating.

Stepping back - I can't believe how much grime and crud were on all of these switches. The polarity switch seemed to have some sort of grease smeared all over the inner PCB. I just can't explain it. But it seems to be a widespread problem with all these calibrators, so I really think one of the best immediate improvements possible are cleaning and conditioning the switches. Once that's done, the unit seems to come back to operation that's very close, if not outright within spec.

[Kleinstein]

Some switches intentionally use some special grease. It protects against corrosion and reduces the wear / friction, so that a higher contact pressure can be used.  A switch designed to work greased may show quite some wear when used dry.

[srb1954]

I have a DP8200. Few mechanical repairs (a few screws and bolts) were needed. However, I have replaced the 100mV output connector on the rear panel.

Can anyone provide some indication as to why this design choice? And also, what exact connector or dongle was being used there.

It might be a low thermal EMF connector. With the 100mV range the LSD resolution would be 100nV so you would definitely have to worry about thermal EMF voltages if you wanted to get reliable measurements at that level of resolution.

Unfortunately the BOM in the service manual doesn't offer any information as to the manufacturer merely quoting the Analogic part number, 25-321036

[Rax]

Some switches intentionally use some special grease. It protects against corrosion and reduces the wear / friction, so that a higher contact pressure can be used.  A switch designed to work greased may show quite some wear when used dry.

That's a possibility, though given the distribution of that (all smeared on one side, mostly away from the contacts), it looks more like a spill of sorts - such as from maybe lubrication on the shaft or something like that. Also, that's the only switch showing that - the rest have only some sort of tar deposit - and I'm not entirely sure why that one switch only (the range switch) would have grease on it.
 
I hope I won't have to open this back up one more time to apply some grease, but I'm not very concerned. It just doesn't seem a very sensitive application. Before the cleanup, the switch was acting extremely sticky and was also downright defective regarding actuating the 100mV mode. I also can't imagine me, or any future user, would actually use this in an extremely high demand capacity (the switch being used hundreds of times a day) like a calibration shop would.

[Conrad Hoffman]

Those switches are just PCB with maybe some special tinning or plating. IMO, fragile enough that a grease is highly recommended. You can get various special Nye products at high cost, or maybe use common Superlube grease. I've talked to their app people and they say it's good as an electrical switch grease and generally safe for plastics. It's a PAO/mineral oil with a fumed silica thickener, plus 5 micron PTFE particles.

[Rax]

Those switches are just PCB with maybe some special tinning or plating. IMO, fragile enough that a grease is highly recommended. You can get various special Nye products at high cost, or maybe use common Superlube grease. I've talked to their app people and they say it's good as an electrical switch grease and generally safe for plastics. It's a PAO/mineral oil with a fumed silica thickener, plus 5 micron PTFE particles.

Well, that explains everything. The main failure mode of these units seems to be the aging of this grease - the "crud," and "tar," etc. I found on these switches was just that - grease that dried, or thickened and whatnot. It degrades so much that it starts both interfering with the electrical contact, and the mechanics of the movement of the switch.

The kind of thing I wish I'd figured at the beginning of this saga - I'd have a figured out a proper grease and have at hand before the surgery and would have applied it as the last step on my restoration work. Well, maybe I'll open this thing at some point later for the third time and go through the switches once more.

That said, I'm pretty sure this is good for a very long time as is. And it works 100% at this point. Happy camper here.

[Conrad Hoffman]

Possibly a squirt of Faderlube could be gotten in there without disassembly? It contains a light oil, which should be better than dry.

[Rax]

Possibly a squirt of Faderlube could be gotten in there without disassembly? It contains a light oil, which should be better than dry.

I did use Deoxit D5 on all contact surfaces of all switches - both PCB traces and the spring leafs - but I guess the difference from that to an actual viscous grease would be enhanced mechanical lubrication.

For now I'll just settle for the level of mechanical lubrication the Deoxit will provide (as a "surfactant" of sorts).