Datron 1281 Repair/Maintenance

[leighcorrigall]

All of Datron/Wavetek 1271/1281 can do 2.35*Full Range, but only in raw mode without any calibration constants applying.

Hi Mickle,

Can you please explain the raw mode? How does one access it?

Thanks.

[Mickle T.]

An asynchronous access to direct ADC results can be obtained via GPIB. I'll try to write some article for it.
Datron 12x1 ADC is much more complex than described in the service manual. It have an auxiliary measurement cycle for DA induced offset compensation, an additional hardware tricks for charge injection reducing and common current cancellation etc.

[leighcorrigall]

...

When I got back to my hotel, I foolishly left the instrument running for several hours to warm up so that I could test it when I got back later that evening. After learning more about the functionality of the instrument in the hotel, I pushed a few buttons and the display information scrambled. No smoke or bad smells, although concerning. The unit was still responsive in that I could somewhat understand what was going on from some of the fragmented information presented and I knew that the unit could switch into various modes. At this point, I turned the instrument off not knowing if it would ever come back. Fortunately, the unit functioned properly the next morning. 

...

The scrambled screen seems to occur at random. After I replaced the capacitors on the digital assembly, I noticed that the problem worsened. I decided to reseat U110 (20L8), U111 (10L8) and U107 (10L8). This seemed to have corrected the problem. I suspect that the terminal release button in the back knocks the U110 when removing the PCB and may have caused problems with the socketed terminations.

Another possibility that caused the scrambled display problem could be that the original PCB insulator does not sufficiently cover the entire PCB surface (see attached). Now that I have identified a damaged card slot (see attached), it is worth ruling out the possibility of contact shorts. Note that some of the plastics in these ageing units are brittle and should be replaced when possible (see attached).

The double-sided tape adhesives cannot be easily removed. The best way that I know of is to apply an acetone cloth to the surface and leave it there to do the removal work for you (see attached). Make sure not to let anything else plastic come into contact with this strong solvent or you might regret it later!

I measured the internal dimensions of the enclosure to be 13.5 mm x 37.8 mm. The replacement material is an Arc-Resistant GPO3 fibreglass sheet with a thickness of 1/32" (< 0.8 mm). I cut the sheet by running an Exacto blade along a metal ruler a few times until it could be creased. The re-enforced fibreglass sheet fits perfectly into the enclosure and slips under the PBC card slots (see attached). No adhesives are necessary because the fibreglass fits the dimensions exactly and will not move around. It is stiff and very smooth. Do not allow the solder joints to catch while inserting the PCB. I might eventually punch holes for access to the 4 screws that secure the transformers, but what would the point be now that the insulator can easily be removed?

If your original digital board insulator looks as badly implemented as mine, I would suggest updating it as well.

[dmmguy]

Hi,

How much you paid for it (if not s secret :-))?

Thanks

[Micke]

Finally!   
Now I am also a proud member of the 8,5-digit DMM club! 
Yesterday I got my Wavetek 1281, the grey version in very nice condition, options 10, 20 and 30.
Seems to be manufactured circa 2001, high serial number 447xx.
Price was 2700 USD (including 25% tax).
Will change electrolytic caps and change SRAM cal-RAM to F-RAM. Only bad thing so far is that this unit has no IC sockets 
It has F/W v3.14, I have not seen this version anywhere to download, so I attach it here.

[leighcorrigall]

Only bad thing so far is that this unit has no IC sockets 

Only the original Datron has sockets that I am aware of.

[leighcorrigall]

It has F/W v3.14, I have not seen this version anywhere to download, so I attach it here.

Awesome! I wonder what the differences are.

[volvo_nut_v70]

Excellent, thank you so much. I've attached my spreadsheet of capacitors and other parts for the calibrators and DMMs. It has manufacturer part numbers for the replacements.

[leighcorrigall]

Will change electrolytic caps and change SRAM cal-RAM to F-RAM.

Welcome to the club.

You should inspect the electrolytic capacitors before purchasing replacements. There are board variations and alterations to the electrical that might be specific to your instrument. Note the lead spacing, outer diameter, maximum voltage and capacitance. I suggest 10,000 hour rating United Chemi. You can use my spreadsheet (attached), which should be fairly complete.

[Micke]

Thanks Leigh!

Thanks for the list, and also thanks to volvo_nut_v70!
Yes will buy premium brand 105C high ripple current and low ESR, and long life time.
I have noticed the limited height in some places, better watch out!
But they seem to have fixed the bodge jobs of the 100µF/50V caps on the Analog board, layout has been changed 
By the way I have a Volvo V70 (2007 Classic) and I am very happy with it!  Bought it new...

[Micke]

F/W v3.14, Serial 447xx
Mod record = 9

[Micke]

Analog board

[Micke]

Analog board (from other direction)

[Micke]

Digital board

[leighcorrigall]

Digital board

Your instrument looks to be in very good condition and I am glad that my digital board uses the most modern variation. What happened to the serial number?

You should speak with xDevs.com if you need a place to post high-resolution images of equipment. 

[Micke]

Digital board

Your instrument looks to be in very good condition and I am glad that my digital board uses the most modern variation. What happened to the serial number?

You should speak with xDevs.com if you need a place to post high-resolution images of equipment. 

Serial number sticker is fine, it was just me that put a bit of silver tape on top to disguise serial number 
Good idea putting pictures on XDevs.com, will take better pictures and put there!
A difference I have seen also is that I have Vishay VLR500 foil resistors on the Current board, not those green PWW.

[TiN]

Micke, thank you for photos and firmware. You can upload anything to FTP server which is mirrored on my repository. Your 1281 seem to be one of latest before Fluke takeover.
VLR500 also ended up used in 8508A later on, as this photo reveals .

[rigrunner]

It has F/W v3.14, I have not seen this version anywhere to download, so I attach it here.

Awesome! I wonder what the differences are.

I've only had a really quick scan of the rom comparing it to v3.12. It appears as though a few commands are not listed in the v3.14 rom.

TRACK_ON
TRACK_OFF
FILT1KHZ
FILT360HZ
AV32

^^^ Aren't in the main block of commands.

[TheSteve]

Perhaps 3.14 was just a bit of a code "clean up" ?

I was planning to burn some EPROMs later today and install them in my 1281.

[rigrunner]

Perhaps 3.14 was just a bit of a code "clean up" ?

A quick look at the 1271 user manual I have shows AV4, AV16 and AV64 as selectable. The 1281 user manual I have shows AV4, AV16, AV32 and AV64 selectable.
A similar story with the FILT commands too.

It could very well be a simple clean up code version.

[TheSteve]

Not a surprise at all but installing 3.14 in place of 3.12 works just fine and passes self tests with no other changes.

[Micke]

Now I have changed all electrolytic caps in the 1281    Thanks to leighcorrigall and volvo_nut_v70 for BOM lists!

Changed those crappy original binding posts that cracks to Pomona 3770 (Copper Tellurium). Bought them from DigiKey.

Put six metal spacer sleeves M4x6,5mm  (S.A Bourqui Jean 99056-70065 / DRM 4370X6,5) before putting new binding posts. Filed down to get the flat edge.
Luckily I had some spacers in the garage... https://www.elfa.se/en/spacer-sleeve-bourqui-jean-99056-70065-drm-4370x6/p/14801677?track=true&no-cache=true&marketingPopup=false

The result with Pomona 3770 looks much better! Too bad they only are available in two colors...

I also installed a switch (in series with F504 or F505 fuse) on the backside that disables filament voltage to the displays to preserve lifetime. Thanks to Dr. Pyta for this advice!  The switch is of the type you must pull out to be able to operate.

BTW, tried to get the pictures (expandable) inline, but without success...

[leighcorrigall]

...

I also installed a switch (in series with F504 or F505 fuse) on the backside that disables filament voltage to the displays to preserve lifetime. Thanks to Dr. Pyta for this advice! 

...

Nice going, Micke.

Can you please elaborate more on your display mode toggle switch? I like it a lot, but I am wondering how accessible the disassembly would be. Is there a disconnect on the PCB where the switch leads terminate? What is the model of the swtich? I think it compliments the original design well.

I am also somewhat interested in modifying my front terminal. For now, mine work well and have not cracked like yours. Just so that others are aware, there are two types of front binding post assemblies -- the type that Micke has (permanent fixture) and the type that I have (mechanical assembly for storage).

https://www.eevblog.com/forum/metrology/datron-1281-repairmaintenance/msg3842057/#msg3842057

[Micke]

The switch seems to be C&K 7101K2ZQE
https://www.digikey.com/en/products/detail/c-k/7101K2ZQE/253351

I just unsoldered one leg of one fuse and soldered in the cables.

[volvo_nut_v70]

I broke the line at PL4 on the Digital board output connector as shown