Gas Discharge Display of Datron 4000 Problems

[nadona]

I just got a Datron 4000 which has display problems as you can see in the pictures.
Both displays are exactly the same. I think they each have 11 anodes and 11 cathodes.

Spent hours and keep looking for possible clues but I definitely need forum members' help. After spending hours trying to look for the filament and grid I finally realized it's not VFD.
Not sure if this will help, but the anode is -67V, cathode segment goes down to -120, and up to -70.

[Balaur]

Are those segment Nixie displays?

For me, it looks like cathode poisoning.

[nadona]

Thank you for the reply.
Datron 4000's all the cathodes are in one flat panel, nothing like Nixie tube but I got a feeling this method might cure the poisoning if it is.

[Paul Moir]

It's not going to be much help (I don't think) but it looks to me like a gas plasma display.  The sort of thing that eventually became plasma displays in laptops (Compaq), etc.

Googling "7 segment gas plasma display" turns up some stuff.  I do remember those in pinball machines.

EDIT:  Wow, there's still some people out there making them: http://www.babcockinc.com/

[edavid]

Left display could be a bad segment driver if you are lucky, or an open electrode pin if not.  You can probably swap segment lines around with some minor surgery and figure it out.  Don't short segment lines together unless you know the driver can handle that.

Right display looks hopeless (gas leak?).

Have you identified the display drivers yet?  Are the displays socketed?

[nadona]

Paul Moir:
The Datron company calls it,"Gas Discharge Display" but I like the word"Plasma."

edavid:
Thanks for the suggestions

What happened: I found out the transistor which drives the left panel bottom segment. While experimenting with the board, all lights are out and the current source in power supply has gone bad, transistor, Zerner, and resistor. I am hoping my local store has all.

[lowimpedance]

BTW the controller is the 8279 keyboard/display driver, (you probably have already found out), quite common in this vintage. I have a Fluke 8840 which uses the same chip.

[nadona]

I had to order the TR(MJE340) to Digikey.

lowimpedance: Are you sure the Fluke 8840 and Datron 4000 use the same chip? Fluke 8840A has VFD display, not GDD. Maybe driver chip is not on the front pcb, but on a seperate pcb?
Thank you for the suggestion.

[lowimpedance]

The Fluke does indeed use the 8279, how ever while it directly interfaces with the keypad the display drive is actually a multiplexed output arrangement which is decoded and then applied to appropriate VFD driver chips
(Also the Fluke 8842a uses it too, since it is just an 8840 with a 20mV and ohm range extra!).
Do you have the schematics for the Datron?, which show the display arrangement.
 

[nadona]

Do I have schematics? I wish I have. No manual for 4000.
Datron's PCB is not PCB either. The board doesn't have part number prints.
Thanks.

[quarks]

Do I have schematics? I wish I have. No manual for 4000.
Datron's PCB is not PCB either. The board doesn't have part number prints.
Thanks.

here you should find almost everything about Datron 4000

www.ko4bb.com/manuals/index.php?dir=09)_Misc_Test_Equipment/Datron/Datron_D4000A

edit: because the link is not working direct, please copy the full text string into your browser, than it works

[nadona]

I knew this page before I bought the calibrator and actually I downloaded all the files.  They don't have the whole manual but some good information about the reference.

Anyhow thank you for the link.

[caall99]

Sorry to bring this one back from the grave. I am dabbling (quite heavily, might i say) in these Datron multifunction calibrators. It appears the left and right displays on these calibrators are the same model, and potentially the same model as used in the 10xx multimeters. I am considering buying some junked units and swapping just the displays to my good unit. Has anyone simply desoldered the display alone and re-soldered it into another unit? Any concerns with that? Any adhesives to work around underneath the display?

Also, i am trying to decide whether or not my culprit is a slowly fading display (due to age), i am experiencing cathode poisoning, or if the display driver circuitry is starting to get "weak". My situation is minor compared to the OP's right display, but i can see some early signs of localized dimming.

Has the OP resolved his issues? Did "freshening" the driver circuitry bring the display back up to par? Would love to hear the end result.

Thanks.

[caall99]

Nadona,

Do you care to share how you resolved your problems? Or are you only performing repairs as a service now?

Thanks.

[nadona]

I had to buy a broken 4000A to get the working displays.

[guido]

Could be something like panaplex. E.g. http://www.tube-tester.com/sites/nixie/data/sp-351/sp-351.htm

I have those in two data precision dmm's. In one of them one display was also not working. Bought an old newport meter to replace it, but the replacement is also bad   Might convert it to LED, but these panaplex displays are much nicer to look at.

[gilbenl]

Hate to dig this up, but its relevant to an issue I'm experiencing. Did some research for my own case and learned that these Datron displays are rather susceptible to cathode poisoning as was mentioned earlier. Good news is that it should be fixable. See links below.

http://electronics.stackexchange.com/questions/87985/7-segment-gas-discharge-display-segments-are-not-lit-up-completely

http://www.tube-tester.com/sites/nixie/different/cathode%20poisoning/cathode-poisoning.htm

https://www.eevblog.com/forum/testgear/datron-1062/msg597101/#msg597101

I'm not particularly eager to start cranking current into a relatively working display, but if the OP is still around and still has the broken display, maybe they would consider doing some experiments.

[woodchips]

Look like the Beckman or Sperry Panaplex displays to me. Have you looked on Sphere in Canada's website?