Televideo 990 schematic?

[JohnKoz]

Hi folks,

Wondering if anyone has, or knows where I can find, a schematic to a Televideo 990 terminal?
I've checked bitsaver and did quite a bit of general searching, all I could come up with is the "Maintenance Manual". You would think this has the schematics in them, but unless it was truncated I did not find it there.

I'd be interested in paper form as well of course.

Thanks

-John

 

[Al Kossow]

it is unlikely you will find it.
by the time the 990 came out the electronics were no longer considered field repairable

 

[JohnKoz]

it is unlikely you will find it.
by the time the 990 came out the electronics were no longer considered field repairable

Thanks for the optimism Al. But I understand what you're saying. This is one of the main reasons why my father quit the TV/radio repair business back then, he couldn't find any schematics and parts were not serviceable. Back then he was using microfiche!

The 990 maintenance manual, seemed like whoever scanned it got tired because it made mention of other sections/pages that weren't there. Maybe someone with a hard copy could verify.

Failing that I'm going to create my own schematic, for the moment I just need the power supply segment of the main board.

-John

 

[MikeI]

Did you ever have any luck finding the schematic?

 

[JohnKoz]

Unfortunately no. I ended reverse engineering one, based on the layout of the board. I loaded an image of the board bottom and traced it.
It took quite a bit of fiddling, and it's only the power half, but it was enough to repair the board I have.
I was also able to glean a few sentences from the Maintenance Manual, that helped me understand the HSYNC, VSYNC and VIDEO signals.
Once I got the power working again, I was able to get some traces with the scope to find out the signal requirements.

 

[cmot501]

Unfortunately no. I ended reverse engineering one, based on the layout of the board. I loaded an image of the board bottom and traced it.
It took quite a bit of fiddling, and it's only the power half, but it was enough to repair the board I have.
I was also able to glean a few sentences from the Maintenance Manual, that helped me understand the HSYNC, VSYNC and VIDEO signals.
Once I got the power working again, I was able to get some traces with the scope to find out the signal requirements.

Any chance of uploading the schematic you created? Thanks

 

[JohnKoz]

Any chance of uploading the schematic you created? Thanks

I could, just let me know where. I'll also caveat that it is only one-half of the board and not guaranteeing that it is error free. But it would at least give someone a starting point.

 

[MikeI]

bitsavers is probably a good place ... I'd like to see the schematic, have a 990 that's working pretty well except for a funky brightness pot