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Osborne 1 and Osborne Executive CRT Monitor issues

MaCJaX

Experienced Member
Joined
Nov 9, 2019
Messages
141
Location
New York
Greetings all and thank you for your help in advance. This is my first post here !!

I just picked up 2 Osborne computers. 1 is the original Osborne 1 and the other is the Osborne Executive. Both coincidentally have the same exact issue. I can not for the life of me get the CRT's on either of them to work. There is no high voltage or neck glow on either. I confirmed that both units have working main boards as I can use an external monitor. I only have 1 shunt. It is the shunt for the Osborne 1 that has the composite out connector on it. This shunt when installed connects the main board the the CRT. Here is what I know so far:

I get 12VDC at the CRT board.
I get about 12Khz on my oscilloscope on the Horizontal circuit.
1 can see adjustments being made on an oscilloscope when I move the brightness control.
I have done a complete electrolytic cap replacement on the CRT board (OCC2) except for 2 caps as I didn't have them. I pulled and tested and they tested good.
I checked the flyback on the OCC2 monitor. I removed it from circuit and used 18VDC and a VOM and got 12VDC across the primary. I would think if this was bad, it would be an open circuit ?

Both CRTs have the same issue. I am not sure why they just don't power on when being supplied with 12VDC. I think I read somewhere that these TTL monitors require a horizontal sync to power on which is present.

Is this a common issue with these ? Is there a component I can check right away that might be the culprit ? Find it strange that both have same issue.

Thanks !!
 
I just picked up 2 Osborne computers. 1 is the original Osborne 1 and the other is the Osborne Executive. Both coincidentally have the same exact issue. I can not for the life of me get the CRT's on either of them to work. There is no high voltage or neck glow on either. I confirmed that both units have working main boards as I can use an external monitor. I only have 1 shunt. It is the shunt for the Osborne 1 that has the composite out connector on it. This shunt when installed connects the main board the the CRT.

I had a similar issue when I recently acquired an Osborne Executive. It started, but wouldn't boot. So I took it apart and cleaned it (replacing the RIFAs while I was there).

I wanted to check the floppy drives, so I didn't completely assemble it before trying to power it up. When I tried, the monitor didn't work.

Short answer: The Drive C: add on that was in it, needed to be hooked to the IEEE488 and external video port. Once I rehooked that up, the monitor worked.
There's probably a way to un-do that, but I haven't researched that yet.
 
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