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View Full Version : Omni II (Kaypro) with bad crt board...



hwrdmltn
January 14th, 2018, 06:59 PM
Hello all;
In this last week I recently became the father of an Omni II (which is a Kaypro II disguised as a logic analyzer).
I have pretty much got it back in service, replacing all the caps on the Astec PS, refurbishing the keyboard with a replaced keyswitch, and the like.
I reached a dead end though. The monitor is not working. It loves the new 12volts it's getting but I have no horizontal sweep, so consequently (for those not in
the know on how they work) I do not get any HV, and of course no pic. It is an Elston DM30-09BO-241-A31 and it appears that a diode in the HV section has corroded not burned
to the point that it disintegrated. It is an Elston (they are still in business and to buy a replacement monitor for a Kaypro is on the order of $348.00).
Without a schematic and knowing what the diode does, I'm unsure of what to guess at. My best guess
is that it is either a clamping diode because it is tied to the yoke coils or it is rectifying some ac for dc bias. pretty hefty though cause it was a round ceramic type but no brown from heat on the board.
It is marked CR408. I also checked the heater in the tube and it appears to be ok at 40 ohms.
Any suggestions would be wonderful. Thanks all for reading.

73's W1ARQ Howard

T-Squared
January 14th, 2018, 09:10 PM
I don't know if this would help, but Tezza had a similar problem a long while back with one of his IBM CGA Monitors:

Tezza's Blog Post:http://www.classic-computers.org.nz/blog/2008-8-23-repairing%20an%20IBM%20monitor.htm
Tezza's Forum Post:http://www.vcfed.org/forum/showthread.php?12052-know-this-diode-IBM-5153-color-monitor-repair

This is just a guess on my part, as I have never had a problem with this system, since I don't own a Kaypro.

Chuck(G)
January 14th, 2018, 11:22 PM
If it helps, I've got a spare Kaypro CRT board kicking around in my hellbox. AFAIK, it works. I'll take a photo if you want.

hwrdmltn
January 15th, 2018, 03:58 AM
Thanks gentlemen;
@T: I viewed Tezza's issue and it appeared that the same issue happened to him as this one. When I touched the leads, the remains of the diode just fell away in dust form. But based on his observation
I have ordered a 3a 1000v fast recovery from Mouser. I suppose the worst that can happen is it just won't work. Thanks for that finger point in Tezza's direction.

@Chuck: If you don't mind the bother of taking a picture, I'd love to see if there is any kind of marking on it - I could not see any due to the fact that this diode's remains didn't even resemble a diode.

Thanks W1ARQ Howard

liqmat
January 15th, 2018, 06:40 AM
It is an Elston (they are still in business and to buy a replacement monitor for a Kaypro is on the order of $348.00.

You have link on that?

hwrdmltn
January 15th, 2018, 10:25 AM
@liqmat: My bad, it was a company that can repair Elston monitors for $358.00.
https://www.controlrepair.com/product/elston-electronics-corp.-dm30-09b0-596-9-inch-monochrome-machine-crt-monitor-12vdc/48054

73's de W1ARQ Howard

liqmat
January 15th, 2018, 11:38 AM
@liqmat: My bad, it was a company that can repair Elston monitors for $358.00.
https://www.controlrepair.com/product/elston-electronics-corp.-dm30-09b0-596-9-inch-monochrome-machine-crt-monitor-12vdc/48054

73's de W1ARQ Howard

Ok, no problem. Yeah, for that kind of cash a LCD mod would be in order at that point. I am a mostly a purist until I'm not. I've seen people gut the Kaypro case and put gaming PC guts inside with a color LCD panel, but has anyone seen or done a LCD mod for the Kaypro keeping everything else original? These tubes are getting harder and harder to find with only a couple of used tubes showing up on Ebay occasionally.

Chuck(G)
January 15th, 2018, 12:57 PM
I dug the board out of the stash. It's similar, but not identical to yours. The component arrangements are bit different and the FBT appears to be somewhat smaller.

The board bears the legend "Micrex, Inc. TW-10594V-0", so perhaps to a different Kaypro model.

hwrdmltn
January 16th, 2018, 09:13 AM
Well, one MUR460 diode and three more caps later on the monitor board, I present to you ... a clean picture with no more horizontal sparkle racing across the screen. It appears to be pretty symmetrical from top to bottom and side to side in spite of the ageing of the yoke and while not obvious by the pics, there is pretty good distinction between lo intensity and hi intensity characters. I haven't cleaned the drives yet so I used a cheat way to get characters on the screen without writing a quick video routine and burning it into EPROM or dragging out the Fluke 9010A. Pic one is without the cpu, pic two is with. This tube may have another good 5-7 years left.

@liqmat:
I would also be very interested in a LCD replacement for these should you find more info. While these are 9" screens, I would suspect some cosmetic mods would be necessary to accommodate those. I would rather it be all original but parts extinction is the enemy for these poor beasts now. I have two Osborne I computers that have pretty good 5" screens but may need a screen someday.

@chuck:
Thanks a lot for your effort anyway but I think the replacement I used was a 4 amp @1000piv so I probably have a way over-rated diode for the application on a mere 9" 12volt monitor. It'll be the last man standing if the rest of it blows.

Next is the drives, and then the logic analyzer board (after I locate probes of course) and hopefully I can find system disks for the Omni II (not to be confused with the Omni 4).

73's W1ARQ Howard

T-Squared
January 16th, 2018, 02:28 PM
Well, one MUR460 diode and three more caps later on the monitor board, I present to you ... a clean picture with no more horizontal sparkle racing across the screen.

Whoa. it worked?! :crazy:

VERAULT
January 16th, 2018, 02:40 PM
Nice Job!

I was actually thinking that lately. Looking into replacing these old CRT's with LCD. I think as more CRTS go someone will have a viable option.

Alphasite
January 16th, 2018, 07:49 PM
If someone came up with an LCD modification that worked with the Kaypro I'd convert the one I have with a bad case and video.

liqmat
January 17th, 2018, 07:40 AM
A proper LCD mod kit for a Kaypro would be an instant purchase for me. This guy gutted his case and installed PC hardware instead. Now only if there was a proper video conversion from the Kaypro motherboard to a modern LCD. I know nothing about of these sorts of things.

https://youtu.be/BFkmO2h-Ius?t=618

I wonder if something like this could be fitted? (I'm just thinking out loud)

http://www.dynamicdisplay.com/product/ge-fanuc-a61l-0001-0076-9-monochrome-crt-monitor-replacement-lcd-2/

hwrdmltn
January 17th, 2018, 03:45 PM
Looking at the specs for this monitor;
http://www.industrial-panels.com/documents/products/fanuc-cnc-control-a61l-monitor-series-brochure.pdf

The Kaypro outputs video, horizontal, and vertical. All TTL. According to these specs, these LCDs are capable of TTL input with 15khz h-sweep with 60hz v-sweep - one of the main barriers that prevents standard VGA on retro equipment because they can't H-sweep any less than 30khz and vertical is usually 75hz or better.

FANUC is industrial equipment. Big bucks. I do believe it could be done. I would love to get one and try it.

You can also make a Kaypro send composite output if you add a ttl IC to combine the horizontal and vertical with the video. Something I will be experminting with in the future.
You can always alter the monitor prom to send console to the serial port - another future prospect I plan to investigate.

W1ARQ Howard