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

[Pipelie]

Thanks, this one is good, but it says 4920M in the code, not 4920.
Combined, LE dump.

It is from 4920, not 4920M. perhaps they share the same firmware. i don't know how to look into the firmware...
you are right, it's  the firmware of 4920M.
I got my unit (4920M) three years ago from eBay Australia.
I try to update 4920M's firmware to 4920 with new ROM. it is working,but revealed 4003 error. no further test for now.
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a couple days ago, I find some pictures of 4920, and notice there is difference in A-D ASSEMBLY between 4920 and 4920M.
turn out the 4920 I said before is actually 4920M, except the front panel.
 

[Pipelie]

here are some photos, you can see,  the front panel of unit say it's 4920, but the label on rear panel reveal 4920M.
 

[Pipelie]

and some photo of 4920, you can compare to the 4920M, as far as i can tell, there is difference in A-D ASSEMBLY.

[TiN]

These are photos of two different meters, right?

Two N connectors are M-version only AFAIK. Perhaps someone replaced front mylar from 4920 

[Pipelie]

These are photos of two difference meters, right?

Yes ,they are  photos of two difference meters.

and   photos I posted at 06:26:52 PM come from my friend, He have a Datron 4920.

[TiN]

Seems there is more to it than just WB/mV-option module, so adding mV-functionality (or WB to usual 4920) wouldn't be as straight-forward, as some hoped.
How is repair going for you?

I will be testing my 4920M soon, once 3458B arrives (enroute now). It's sitting cold all that time so far  .

[CalMachine]

What's weird is, the 4920M comes default with the wideband module (AFAIK), where as the 4920 has a discrete wideband module (the 4922).

[TiN]

Having bouncing around modules for wideband ain't reliable enough for military, man .
I wouldn't complain though, mV is easier to get by DIY means than shmick tested 50MHz TVC module..

[CalMachine]

Having bouncing around modules for wideband ain't reliable enough for military, man .
I wouldn't complain though, mV is easier to get by DIY means than shmick tested 50MHz TVC module..

Yeah, you've got a good point there.  and that image is awesome! hahaha


Aww snap! Those Navy Metcal stickers!  I see those on the regular, as the US Navy is one of our biggest customers.

[CalMachine]

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

I wonder who would be releasing such software 

I am attempting to try to write some code to utilize our 4920 and 4920M to get automated testing done.  This thread has definitely helped a lot!  I'll be looking into those Swerleins algorithms too!  Really intriguing stuff here...

[Pipelie]

Seems there is more to it than just WB/mV-option module, so adding mV-functionality (or WB to usual 4920) wouldn't be as straight-forward, as some hoped.
How is repair going for you?

I will be testing my 4920M soon, once 3458B arrives (enroute now). It's sitting cold all that time so far  .

after replaced the SRAM(m5m5256) and a bunch of electronic capacitor,  the unit back to the working condition, but every time I turn it on Running internal self-test reveals  one error: 4053, WB calibration validity. I try to Run the WB Wlinearity self-cal, but didn't Successful.
any suggestions are welcome.

[ap]

It looks like your item needs calibration. This is not always that easy, because it seems the different cal routines sometimes influence each other. TIN I think had the same experience. So a full cal may be needed.

[Pipelie]

Thanks for the reply,
I'm looking forward to read TiN's  article about 4920's calibration.
couldn't fix my 4950 this weekend, but GOOD NEW, My 4920 pass all self test without error,when the room temperature around 20C. no more error 4053.

[ap]

What did you do to fix the 4053-error?

[TiN]

My poor box died, just from sitting unpowered on the desk.
4014 error, -19V supply for A/D. It's simple LM337 there , what could go wrong? 

[Pipelie]

My poor box died, just from sitting unpowered on the desk.
4014 error, -19V supply for A/D. It's simple LM337 there , what could go wrong? 

It mostly due to the cap near to LM337( connect to the output of LM337), I have this -19v supply problem before when  I repaired my 4920.  desolder it and test the cap or test it on board.

[Pipelie]

What did you do to fix the 4053-error?

run the wideband calibration and don't forget to update the calibration date once a year at least.

[TiN]

Pipelie right on money. Replaced 1uF 100V caps, and thing is alive again. 
Lesson: don't ignore little electrolytic caps during repairs on old instruments 

[chinapp]

anyone know how to upgrade the mV option of 4920? I upload the FW of the 4920,it's NO is 400978,ver 1.14,I can find the strings of the mV option in the FW,maybe a decompile can find something.I am a newbie on this

[TiN]

Don't understand what you mean. If you have 4920 it already have mV option installed, no?

[chinapp]

NO, my 4920 has no mV option, when I press the mV, it said :1014 error,no mV option fitted
 
I opened the aliminium box beside the analog board ,it should be the mV option ,there are some ICs  not fitted (see attachment)

,I wonder is there some way to upgrade the mV option

[TiN]

Interesting. I didn't think there are 4920 without mV option.
I don't have 4920 so can't tell what's there missing parts are, perhaps somebody who repaired 4920 could help.
My 4920M has only wideband option in place instead of mV.

[chinapp]

yes, I checked the FW of 4920 and 4920m,seems have much differences,4920M FW has some strings of 1281

the 1281 can use the short link to choose the options, did not find  short link for 4920 to choose option

[ManateeMafia]

I think I see a blown trace on the left side of the pcb just between the two resistor packs.

[TiN]

It looks cut on purpose, not blown