View Full Version : Osborne 1 and Osborne Executive CRT Monitor issues

November 9th, 2019, 02:40 PM
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 !!

February 5th, 2020, 10:40 AM
Have you found out the problem ?
Maybe the shunt connector is not the correct one for using the internal monitor.

Here is a link to the service manual which explains on page 43 the connections needed.