Restoration : Wavetek 4920/4920M teardown, repair and usage cases, come join!

[acbern]

Same seller? I see same thing. But that's expected, as flatness and other special cal constants are lost too.

No, thats not expected. You calibrate 50kHz, 200kHz, 500kHz and 1MHz, and inbetween it should be flat. Mine is not. So something else is wrong too. If you have that issue as well, then you should not go to a CAL lab yet. So I recommend you calibrate based on your K2001, and then apply test signals between calibrated spot frequencies, just to check.

[zlymex]

One of my Chinese friends also bought one from the same seller(the $481 one). He hasn't got it yet but seeing from the photo of the transshipment the unit is a 4920 instead of 4920M

[TiN]

pelule
You are the man. Thanks.
I rehosted all files on 4920M article (in works).

zlymex

He hasn't got it yet but seeing from the photo of the transshipment the unit is a 4920 instead of 4920M

Maybe his got millivolt option then?
Invite your friend to join us here  EEVBlog metrology section would not be even remotely as good without your contributions 

acbern
Ok, I'll check more in details with some python snake help.
Perhaps 10Hz - 1MHz in 10kHz steps on 1V,3V,10V ranges would suffice?

[acbern]

TiN,
actually if you want to make that many steps, thats fine, but for starting, 50k or 100k steps is probably more than enough. I see this when calibrating at the 4 given steps (10V; 50, 200, 500, 1000kHz) and testing inbetween (1kHz, 100kHz)... So even works with just a few manual checks, even no SW needed initially.

[pelule]

The 4920M vol 1 and 2 are on KO4BB but not the others. Maybe have another go with those, anyway thanks for sharing.

Uuups. I have checked KO4BB first, but didn't found them. Anyway, a 2nd place is better than none.

[zlymex]

Uuups. I have checked KO4BB first, but didn't found them.

The 4920 manuals are not under Datron or Wavetek sub-directory, have to search.......

[zlymex]

zlymex

He hasn't got it yet but seeing from the photo of the transshipment the unit is a 4920 instead of 4920M

Maybe his got millivolt option then?
Invite your friend to join us here  EEVBlog metrology section would not be even remotely as good without your contributions 

Thanks TiN. 4920(without M) probably got the millivolt option, he is even glad when he knows the non-M version. Some of my friends visit EEVBLOG often, but they seldom/never speak here probably because of the language.

[acbern]

It turns out the 4920 had not only lost its special cal constants but also all of its normal routine calibration parameters (even though the battery was good, maybe someone deleted it actively). That looks as if it explains the deviations at different frequencies. So doing routine cal and then special call seems to result in correct behaviour.
What is strange though is that in the 30V and 100V range, where the 1MHz routine cal is made at 20V only (not its maximum, due to limitations of calibrators), I need to use SET to set the voltage to 20V, otherwise it calibrates at erroneous voltages. This however is not in the documentation, and the other levels (e.g. in the 30V range at 10V and 30V 1kHz) are recognized automatically. Can anybody confirm?

[TiN]

That what I was referring to, all constants are lost, so full special+normal recalibration is required. I don't have source capable to generate 20V 1MHz, but I'd expect your assumption is correct, based on manual description of calibration procedures and function.

[TiN]

Today's haul. Guess what will be happening this weekend?



Also spot the special type of the part on the photo for the free bonus!

[Vgkid]

I'm curious to know, what you use that oled display for.

[Dr. Frank]

Today's haul. Guess what will be happening this weekend?

I already know, what's going to happen, so I'm out of this contest..

But that RF connector stuff looks like mine, when I'm doing precise AC/DC transfers. 

Frank

[TiN]

Dr.Frank

The only catch though, that there will be no AC/DC transfers happening, as there is no TVC's anywhere near my reach.
It will be AC/AC stuff purely. More to come soon

Vgkid
I'm curious about that too. Saw it on the shelf during check-out, couldn't resist not to grab one.

I'll cut the suspense on the special type - it's those red capacitors, Wima MKC. Didn't expect to see them in stock, I heard polycarbonate film caps are out of production long ago. So to feed the greed, bought 10pcs to collect dust on my shelves

[lowimpedance]

Sorry for the thread spam...but..
 Everyone should have a stash of carbs in the cupboard  .
Quick peek at some well aged ones in my pile (not stale yet i don't think !).
And a bonus pic of a 'fat' styrene next to a carb   (also need a good styrene stash to share the dust too!)

[TiN]

We want to know the story behind metal box with array of switches 

[lowimpedance]

Ahh.... some things are best kept secret 

[TiN]

Time to hit the road. Mobile calibration lab, lol. 3458 and 4920 are about to see some 360km/h train love. 36kg , just below 40kg limit .



Maybe USA has ebay, but Taiwan have it's pros too, it's small and no need airplanes to visit other city.

I hope I'll be allowed to take few photos of calibration mayhem planned to happen

[TiN]

Phew, 4920M is back home now...



mini Cal-fest TW was a blast, very happy with this weekend. Spent 20 hours or so cooking python snakes, talking to calibrators and Fluke AVMS, and learning 4920M cal quirks.
I now sorta understand why Tektronix wanted 7000$ for 4920M cal.

Did not had enough time to run WB cal or extra steps, so I'll still have to calibrate few things, but I can do those at home using my 3245A and 3458A w/Swerlein's algorithm for precise AC.
Most difficult high voltage ranges are calibrated now. I ran both low-level calibration and user calibration as you may remember, cal rom was erased in this unit.

I'll post more info once I get everything prettified.

Btw, 4920 is very capable instrument. During second user-cal check, I was watching for readings, they match well <10ppm on each range/freq (1kHz,1MHz) to 5790A. So these old gems are truly capable.

[lukier]

Did not had enough time to run WB cal or extra steps, so I'll still have to calibrate few things, but I can do those at home using my 3245A and 3458A w/Swerlein's algorithm for precise AC.

I googled Swerlein's algorithm, read the paper and googled if he published some other interesting papers, but found much darker history instead:

http://www.thedenverchannel.com/news/homeowner-arrested-after-explosives-found-in-longmont
http://www.dailycamera.com/ci_16600312

[pelule]

Here are some "Swerlein's algorithm" documents. It may help.

[Dr. Frank]

I've salvaged the Swerlein program, an executable file, and already sent TiN.
Whoever else is interested, may contact me
Frank

[plesa]

Here are some "Swerlein's algorithm" documents. It may help.

Thanks for sharing. Is there any reason why this algorithm is not part of firmware 3458A?

[TiN]

I think 4920 are underrated instruments. During calibration readings to 5790A were more close (<10ppm usually) than I expected. 

[Vgkid]

Good job on the fix, how long did it take for you to cal the 4920?
One of the local labs has a 792A, and a 5790A.

[TiN]

Well, its a difficult question.
Techically calibration is ~30min for user calibration and about 2 hours for manufacturing one, however this is with automated setup with Python snakes and using 5720+5790A. If one after best accuracy, TVC or 792A would make things much slower with nV-meter. I'd plan for at least 2 full days, if you have working software to do all steps.
Also its picky so some steps may not pass, few multiple runs would be needed.

You also need 5700/5720 and 5725 booster to calibrate 300V and 1kV ranges, as base 57xx cannot go >219.9999V for >1kHz. On positive side, you can leave those ranges out , as calibration steps are per range/freq.

I heard there may be software available somewhen next year to do such 4920 cal