Now my humble lab welcomes those rare green-glow Datron/Wavetek magical pieces. No, not another 8.5-digit Datron 1281...
![Tongue :P](https://www.eevblog.com/forum/Smileys/default/xtongue.gif.pagespeed.ic.J5mTe0A2NA.png)
We talking AC-nuttery this time, time to open new pandora box for me. Yes, it's Wavetek 4920! And not just any, but military version of it, 4920M.
![Fighting :box:](https://www.eevblog.com/forum/Smileys/default/fighting0030.gif.pagespeed.ce.H3HVtgjLEV.gif)
What's different from "regular" 4920? From what I found out , M-version have next differences:
* Both N connectors for input, instead of N for WB and banana for regular
* No low mV ranges option
* More scarce menu system and few differences in features
I hence summon all Datron/Wavetek 4920 and 4920M owners to join me in this ACV-nuttery journey begin.. I know you folks are out there, hiding gems behind DC gear!
There was recent sale of 5pcs Wavetek/Datron 4920M. Instead of waiting and hoping that some voltnut from EEVBlog will snatch one and show us it's insides, I decided to close ebay shopping year 2016 for me with this last bit, which happened to have more recent Wavetek-only branded 4920M. Is it a bust for 592$ or a "winner-winner chicken dinner"? Well, in worst case it's just another box with LTZ1000 reference inside and nice glowing VFDs
![Evil >:D](https://www.eevblog.com/forum/Smileys/default/xevil.gif.pagespeed.ic.tdrs7Uj5gu.png)
After some waiting on GSP shipping and delivery (which is great btw, packing on GSP is top notch!) box just arrived today. Excited? Hell, yea.
Will it be another 220+ hours repair project, like rusty 3458A? Perhaps even more so, as I have not much experience in AC stuff, don't have any thermal converters, and only calibrated measurement piece of ACV/ACI I have is Keithley 2001 with Tek cal from 2014.
My 3458A had never ran SCAL, nor 2002's completed AC calibration. Anyhow, stay tuned, will be fun!
![Indifferent :=\](https://www.eevblog.com/forum/Smileys/default/indifferent0023.gif.pagespeed.ce.nyXMDasYXd.gif)
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/w4920m_face_1.jpg)
Break the rule "take it apart" and actually power this unknown black cat to see if she's alive.
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/w_vfd_1.jpg)
VFD is unusual nice and emerald green. I actually dig it, looks way better contrast than Keithley's/3458A. Big digits too! I think it's same exact front panel as used in other 1271/1281/4950 Datrons.
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/w_caldate_1.jpg)
Last cal January 2015? Really? Too good to be true, I say.
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/w_callabel_1.jpg)
And calibration sticker says 2009. Sticker on the rear tells to replace battery in 2012, so it's 4 years overdue or someone did not bother to update sticker?
Running internal self-test reveals only one error: 4053, WB calibration validity..
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/w_diagfail_1.jpg)
No other issues reported. Running WB Wlinearity self-cal (lucky me, it's the only calibration available which does not require fancy AC sources and gear).
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/w_wbvcal_1.jpg)
After ~10 minutes, self-test pass without single error..
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/w_calpass_1.jpg)
Is it like a fairy-tale and one of those repairs where nothing was broken?
Only one way to find out, connect ACV input and see what's out there.
* Set 5.66ACV 50Z on
my trusty HP 3245A source, which gives pretty close to 2V with 50ohm load. Frequency for test is 100e3 Hz
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/hp_w_1.jpg)
2.122V? huh?
![Huh? ???](https://www.eevblog.com/forum/Smileys/default/xhuh.gif.pagespeed.ic.6Nvt7O8a11.png)
What HP 3458A has to say about it?
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/hp_hp_1.jpg)
1.9984V! But we never calibrated HP DMM for AC.
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/hp_kei_1.jpg)
1.9962V from Keithley... Now i'm sorta believe those two folks more, not the Wavetek... Uh, oh..
![Scared :scared:](https://www.eevblog.com/forum/Smileys/default/scared.gif.pagespeed.ce.oZptHNcbsD.gif)
I ran manual step tests via Pathway section as well.
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/w_pathway_1.jpg)
All steps pass with range stated in service manuals (Thanks to ManateeMafia for scans!), except one :
Test 4035 (PA22) : AC RMS Conversion - Linearity (10V)
Expected in manual result: 2.350 < x < 2.450 V
Unit reported : 0.242792
This one sounds somewhat important don't you think?
So I tested various input signals 1kHz from
Time Electronics 9823 calibrator on various ranges.
2V on 10V range gives 2.007988V (K2001 reports 2.00053)
same 2V on 30V range gives 3.30198V. What?
![WTF? :wtf:](https://www.eevblog.com/forum/Smileys/default/wtf2.gif.pagespeed.ce.pxLiY5pjs4.gif)
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/test_2v_30v_1.jpg)
Similar problem on 200mV range
![Rant :rant:](https://www.eevblog.com/forum/Smileys/default/rant.gif.pagespeed.ce.koOB_HE-VX.gif)
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/test_200mv_3v_1.jpg)
Few more steps:
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/test_10v_10v_1.jpg)
![](https://doc.xdevs.com/doc/Wavetek/4920M/img/test3_1.jpg)
Next step - you already know it
![Broken! :-BROKE](https://www.eevblog.com/forum/Smileys/default/smiliey_scope_broke.gif.pagespeed.ce.z9RuKVWKjY.gif)