Author Topic: DATEL Voltage Calibrator DVC 8500, Repair [SUCCESS] (Read 25951 times)

HighVoltage · « **on:** May 06, 2016, 07:54:40 pm »

I bought this broken DATEL Voltage Calibrator DVC 8500 and just received it.
Starting this thread before I start the repair.

This seems to be a very nice little calibrator with good specs:
+/- 19.999 V
+/- 25ppm accuracy

First thing to notice is a broken mains cable, it is like falling apart to dust.
May be I will upgrade it to a real mains connector.

I did find a nice Datasheet, even with calibration instructions, here:
http://www.calibratorsinc.com/images/DVC-8500_DATA_SHEET.pdf

The lever switches are moving with difficulties.
Does anyone here have experience with these lever switches.
I don't think they can be taken apart.
May be I can clean/grease them from the front, hmm ... will be interesting.

I first need to get a tiny torx to open it.

HighVoltage · « **Reply #1 on:** May 07, 2016, 11:42:37 am »

Ok, next step in repair....
Installed a 3 pin mains connector with capacitor across the mains and a new fuse holder.
This looks much better already.
Now comes the electrical output testing.

HighVoltage · « **Reply #2 on:** May 07, 2016, 12:51:37 pm »

The output voltage was all over the place and not even one one value was correct.
Obviously the switches got corroded or contaminated or just old.

So, I drowned the complete front end of the calibrator in to pure alcohol and moved the switches probably a hundred times each.
A lot of dirt came out to to the front.
Then I had the alcohol evaporate in an oven for a few minutes at 50 degree C

And then I filled the switches with my trusted "super contact cleaner, with poly phenyl ether" and moved the switches another hundred times each - at least. Then I took compressed air and blew the access lubricant out.

And ... look at this...
All values are working perfectly.
It looks like I do not even need to do a calibration.

But I might have to exchange the potentiometer since it jumps the values a little. But this is an odd little 50k Pot with a tiny shaft.
Ok, time to take some measurements and histogram for each value, to see how stable it is.

Too bad there is no full schematics available for this little unit.
It has a 10.000 V Ref output in the back.
I will take some statistics measurements there as well.

Kleinstein · « **Reply #3 on:** May 07, 2016, 04:32:44 pm »

The circuit does not look that complicated. So reverse engineering should be possible, if really needed.
The transformer looks quite large for just a calibrator.

HighVoltage · « **Reply #4 on:** May 07, 2016, 05:57:02 pm »

Quote from: Kleinstein on May 07, 2016, 04:32:44 pm

The transformer looks quite large for just a calibrator.

Very true, especially since I am using a 100mA Fast fuse and it holds perfectly.
I will make some measurements on the transformer output to see what the real power is.

The potentiometer needs to be exchanged for sure.
But besides this, it works perfectly.
I have it hooked up to my 34461A and will collect output data over night with histogram

HighVoltage · « **Reply #5 on:** May 08, 2016, 10:24:21 am »

kept the calibrator on over night and this is the result.
It was sitting on the bench without housing.

The 34401A shows 20.000V and does not move at all.
The temperature changed by about 3 degrees during the night.

This is not a bad result for such a small calibrator that is so old.

HighVoltage · « **Reply #6 on:** May 08, 2016, 03:22:08 pm »

All back together. Installed new foam for the front bezel to not be loose towards the panel.
Looks really good and works extremely well.

Tested in all ranges and all of them agree with my trusted Agilent 34410A.
It is a really nice LM399 based reference.
I will keep it running for a while and take some long term stability readings.

Anyone interested in such a small calibrator, I can only highly recommend getting one.
They are cheap when broken and easily repaired.

dom0 · « **Reply #7 on:** May 08, 2016, 06:29:54 pm »

Quote from: HighVoltage on May 07, 2016, 05:57:02 pm

Quote from: Kleinstein on May 07, 2016, 04:32:44 pm
The transformer looks quite large for just a calibrator.

Very true, especially since I am using a 100mA Fast fuse and it holds perfectly.
I will make some measurements on the transformer output to see what the real power is.

They specify 10 watts (a bit much, probably only needs a fraction of that). Due to the compact assembly it might be that they used a larger core than necessary and a lower flux than possible to reduce heating of the transformer and stray fields.

HighVoltage · « **Reply #8 on:** June 17, 2016, 03:37:13 pm »

I just bought another one of these little calibrators.
This one was sold as dead for $50, so a real bargain if I get it repaired.

And ... the only problem it had was a broken mains cable.
I will also install a mains connector on this one.
But I probably need to attach a big warning label for 120V only, since this one came from the USA

Here are some pictures.
This one looks newer than the previous one.

HighVoltage · « **Reply #9 on:** June 17, 2016, 03:38:50 pm »

And some more pictures.

When I am done with the repair, I want to run a few comparison test's between both of the calibrators.

dr.diesel · « **Reply #10 on:** July 13, 2016, 03:24:42 pm »

I scored one of these cheap on eBay as well not too long ago, power cord in the same condition! Neat little device, still on the bench awaiting repair.

HighVoltage · « **Reply #11 on:** July 13, 2016, 03:35:32 pm »

Great, that you got one, they are indeed neat little calibrators.

They really put attention to detail:
The white cable that runs to the front power switch is even shielded to the housing.

The second one I got is also working perfectly, just needs a little calibration and is warming up.
I also installed a plug in the back for the power cable and it works and looks really great.
A new fuse is also installed, with a 100 mA fast glass fuse.
Here is a picture of the mod:

dr.diesel · « **Reply #12 on:** July 13, 2016, 03:44:39 pm »

^ Nice mod.

From the date codes mine is from around 1988, hopefully nice and thoroughly aged by now.

dr.diesel · « **Reply #13 on:** July 13, 2016, 04:32:19 pm »

Ok, you inspired me. Cord replaced, but no other changes, so no contact cleaning, no calibration, factory caps etc.

It's now warming up (inside enclosure, front panel 2-wire test) and I'll trend it against my K7510 overnight.

dr.diesel · « **Reply #14 on:** July 14, 2016, 11:24:19 am »

The low spike at about 1700 was caused by a 3 degree F temp drop when storms rolled in last night.

8500 was set at 10v.

HighVoltage · « **Reply #15 on:** July 14, 2016, 11:58:56 am »

Nice that you got it to work.
Can your K7510 output the statistics of this plot?

When you wiggle the small levers just a little in different positions, is the reading stable?
I had to clean the switches in both of my units.

After I am done with the calibration, I will run both of them against my meters.
With your data in addition, we can get a good uncertainty of these calibrators.

dr.diesel · « **Reply #16 on:** July 14, 2016, 12:03:15 pm »

I'm going to clean it up, check/replace the caps etc, then I'll do a proper test with statistics.

dr.diesel · « **Reply #17 on:** July 14, 2016, 12:11:28 pm »

Ok, as arrived from eBay, only mod was the cord replacement.

HighVoltage · « **Reply #18 on:** July 14, 2016, 07:12:49 pm »

Your calibrator seems to be very stable.
It probably needs a little correction with the dial right in the middle.

Great screen shot of your Keithley 7510.
Very nice that you also get the Pk/Pk measurement in the statistics screen.
I am missing that on my Keysight meters.

HighVoltage · « **Reply #19 on:** July 17, 2016, 10:48:14 pm »

Here is a measurement of my 120V AC mains unit after about 4600 readings
At 10V setting of the DATEL calibrator I seeing about +/- 10 uV up and down
This unit is not fully calibrated, that is why the dial is turned a little clockwise to be at 10.000 V output

dr.diesel · « **Reply #20 on:** July 27, 2016, 07:28:08 pm »

Happen to find a schematic laying around the internet somewhere?

Mine has two 470uf 63v axial caps bodged in on the power supply side, wondering what the originals were?

dr.diesel · « **Reply #21 on:** July 28, 2016, 02:18:36 pm »

Either of your units happen to still have the original caps?

HighVoltage · « **Reply #22 on:** July 28, 2016, 02:58:49 pm »

Schematic is not available, as far as I have searched.
Your caps look original. Both of my units had the same bodged / extended wires on the negative side.
I will take another picture tonight.

Did you find good replacement caps?

dr.diesel · « **Reply #23 on:** July 28, 2016, 03:21:18 pm »

Wow, OK, that surprises me. My plan was to return it to factory condition for a thorough before modification test run, oh well.

Since I have two of these in my spare bin, think I'll use them:

https://www.digikey.com/product-search/en?keywords=565-4030-ND

Factory caps measured good at ~80mOhm.

HighVoltage · « **Reply #24 on:** July 28, 2016, 04:21:27 pm »

Your Digikey link does not work.

Here are two pictures of my first unit.
This is a 230V transformer EU edition.


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Author Topic: DATEL Voltage Calibrator DVC 8500, Repair [SUCCESS] (Read 25951 times)

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