Datron gas-discharge display -- slow turn on? - Page 1
Forum section: electronics / general

author: essele
author_rank: Frequent Contributor
timestamp: September 08, 2020, 11:53:20 am
content: A question for all the Datron fans out there ... I've got a 4000A with the two gas discharge displays and the right hand one is showing some strange turn-on behaviour.From "cold" (and I mean unused for a while) the right hand display takes a good few seconds to turn on (probably 10-15 seconds) and then is fine. If it's "warm" (used recently) then there's no delay, and the delay does seem to be related to the time it's been off.I've just tested it and the left hand display is fine and seems to work instantly (certainly quicker than the right hand, but you need to press a few buttons to get the display to do something, so it may not be instant!)So it feels either temperature related or some capacitor charge type issue ... however it's very strange that it's only affecting the one display as I can't see much on the schematic that's unique to the right hand side only that would affect the whole display rather than segments or digits.Does anyone know if this is an indication of an impending failure of the display, or do I need to be troubleshooting other things? (Which is painful because it takes hours to get back to the "cold" state again.)Schematic attached for reference.Thanks,Lee.

author: essele
author_rank: Frequent Contributor
timestamp: September 08, 2020, 08:51:32 pm
content: Hmmm ... looking at this again I’ve just spotted C1/R26 which looks like a 1s delay at startup on the inhibit pin.I don’t understand how this could impact one side and not the other but definitely worth a look as I haven’t done any cap changes on this board!Later update (since I didn’t hit submit when I thought I did) ... I changed the four tantalums on the board (they all measured ok, but I changed them anyway). There was also a small black corroded/burnt area near two connector pins which seemed to be conductive, so I scraped that all out and filled it with UV curing glue. I also cleaned off some other areas of corrosion.Anyway ... it now appears to be working.(Do they really need that many screws in the display pcb!!!)Lee.

author: Gyro
author_rank: Super Contributor
timestamp: September 08, 2020, 09:22:15 pm
content: Good that you have found something. I guess you haven't had time to check the extended power-off situation yet.Panaplex type plasma displays can suffer slow startup after a prolonged period of disuse, particularly if not exposed to direct light. This is due to the absence of free ions which help initiate the glow discharge.The displays have left and right 'keep-alive' cathodes (LKA and RKA) and associated anodes (ALKA and ARKA) which provide a constant source of ionisation to help with fast turn-on when the displays are operating - both for multiplex operation and lighting new digits, polarity indicator etc. but of course these can't help when the unit is powered off.If the display drive voltages are correct then you can probably put this down to normal display behaviour (I have a Datron meter that does the same thing).

author: volvo_nut_v70
author_rank: Regular Contributor
timestamp: September 08, 2020, 10:21:23 pm
content: This Dale manual/design note on the plasma displays may answer some questions..............

author: essele
author_rank: Frequent Contributor
timestamp: September 09, 2020, 09:40:40 am
content: Thanks for the info ... very interesting.I'm not going to open it all up again, and I probably should have mapped it back to the schematic at the time, but the carbonised area was in the J1 90's region, which interestingly (and probably somewhat obviously) contains the -175v supply amongst other things.I powered on this morning and it all seemed ok, however I think I'm going to need it off for an extended time before I really know if this has worked or not. If this isn't the fix, and it's a more generic issue with the displays then it doesn't actually sound terminal.Cheers,Lee.

author: volvo_nut_v70
author_rank: Regular Contributor
timestamp: September 09, 2020, 02:20:28 pm
content: Glad it works now. If it is a display you probably know that a Datron 106X is a donor or there are a few new displays available (NOS) through Mouser, I can forward you the info... It works out to USD$200 each

author: branadic
author_rank: Super Contributor
timestamp: September 09, 2020, 05:08:07 pm
content: Mh, we should have a group buy then, instead of killing working meters.-branadic-

author: Gyro
author_rank: Super Contributor
timestamp: September 09, 2020, 06:05:42 pm
content: As long as the display segments are evenly lit, there's nothing to suggest any sort of upcoming failure. They are very long lived.This is when you need to start worrying...

author: essele
author_rank: Frequent Contributor
timestamp: September 10, 2020, 09:26:46 am
content: Hmmm ... just did a turn-on test, took about 5 seconds, so not fixed. For the moment I'm going to chalk it up to the absence of free ions rather than a fault.If it does turn out to be faulty, I do have a "spare" 4200 I could use as a doner, but to branadic's point, I'd rather not destroy something that's (mostly) working. I'd be happy to spend $200 to have a spare display just in case!Lee.

author: branadic
author_rank: Super Contributor
timestamp: September 10, 2020, 09:50:17 am
content: QuoteWell, here is the price that Mouser asks:1pc.: 151,01 €5pc.: 146,48 €10pc.: 142,08 €So it's worth the money to have it original.-branadic-

author: essele
author_rank: Frequent Contributor
timestamp: September 10, 2020, 10:09:57 am
content: What part number are you using? Everything I've looked at so far just says "SEE DRG" and the drawing only has the Datron part number??

author: MadTux
author_rank: Frequent Contributor
timestamp: September 10, 2020, 10:48:14 am
content: Grabbing the drive signals at TTL level and use them to drive a LED display is no option?Or build something like an attenuator board for the HV lamp drive signals and use them to drive VFD grid?Is it that one:https://www.ebay.com/itm/Datron-Fluke-4000-Autocal-Standard-Calibrator-DC-Voltage-Current-Resistance-/184374145071?hash=item2aed8e302f%3Ag%3AHbIAAOSwYm5fGbfz&nma=true&si=BIz1c9SUQGvE2P3UiHWt1%252BW6j7I%253D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557Looks like the electrodes are poisoned or the coating is separating, so it's no longer conductive. Have seen similar things on neon lamps. Before scrapping them, I'd try overvolt them and see if the poisoned areas can be "burned" away.

author: branadic
author_rank: Super Contributor
timestamp: September 10, 2020, 11:07:30 am
content: Quote78-PD009D06401G02-branadic-

author: Johnny10
author_rank: Frequent Contributor
timestamp: September 10, 2020, 11:39:17 am
content: My 4000A right display can take over 30 seconds to come on.It is dying though with weak segments.That is interesting Mouser has new ones for sale.Lots of Datron users would be interested at around 125 I would imagine.I love those displays. Bright, easy to read at a distance.

author: maginnovision
author_rank: Super Contributor
timestamp: September 10, 2020, 02:58:29 pm
content: Quote from: branadic on September 10, 2020, 11:07:30 amI've got 3 good spare displays and now I feel like I should be ordering some just to be sure.

author: Gyro
author_rank: Super Contributor
timestamp: September 10, 2020, 06:10:59 pm
content: Quote from: MadTux on September 10, 2020, 10:48:14 amI've certainly had success with rejuvenating the odd segment on a Panaplex display, that was on 105x unit though, where the display is made up of separate socketed 2 1/2 or 3 digit standard Sperry/Beckman/Babcock SP35x series displays. Running at elevated current can indeed restore dead area. Beware though that any material sputtered off can settle on adjacent segments or the front glass. A whole multiplexed display would be a challenge though, unless you can push up the overall driver current setting sufficiently without killing it.Most plasma displays will still be looking healthy long after their VFD cousins have died though, or their uneven brightness has made them too horrible to use (which happens a lot sooner).

author: syau
author_rank: Frequent Contributor
timestamp: September 10, 2020, 10:55:00 pm
content: Quote from: branadic on September 10, 2020, 11:07:30 amIt shows no stock