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TRS-80 Model III

J

jburke71

New Member
Joined
Jul 15, 2007
Messages
5
Location
St. Louis, MO
Well,

I just became the proud owner of a TRS-80 Model III (The Model I was the first computer I used), but it looks like the vertical sync is messed up. When I turn it on the system boots (even runs a disk), but the screen keeps shifting up (the way old TVs used to). Is there an internal control for this somewhere?

Along with this, I got around a 100+ application disks. I guess I'll look into converting those over to a modern format for prosperity.

Any thought's on the sync problem are most welcome (along with suggestions for care and feeding of this beast).

Thanks,

Jason
VCF Newbie
 
According to the Model III service manual, on the video driver board (the one mounted on the inside of the case top), in Zone 3-D (numbers down one side, letters across the top of the PCB), there is a potentiometer (R-612) that is the vertical hold adjustment.

You can try adjusting this control (of course you'll have to have the unit on) and I'd use an small insulated slot screw driver and stay away from the CRT, it bites (at about 12KV).
 
Thanks for the information! Will the CRT jump out and bite me (high voltage arc), or do you have to touch it? 12KVs doesn't sound at all pleasant, so I want to make sure to take any possible precautions.

Thanks again,

Jason
 
Nah, shouldn't. Just take off any rings or watches before you start and, as an old technician adage, work with one hand in your pocket.

It's 12KV, but, not a lot of amperage, but, if you snag it, you're going to feel it, believe me.

It's not going to turn you into ashes or toss you through a wall, but, you'll know LOL

Disclaimer: I hold no liability of you kill yourself fixing this. I just told you HOW to do it, not TO do it. :)
 
Druid6900 said:
According to the Model III service manual,
Click to expand...
It probably is a FAQ, but is that manual available somewhere? I found some technical documents on the Internet, but am unsure exactly what they were. I have a feeling soon I will need to consult it, or I will simply just ask you in public or via PM.
 
carlsson said:
It probably is a FAQ, but is that manual available somewhere? I found some technical documents on the Internet, but am unsure exactly what they were. I have a feeling soon I will need to consult it, or I will simply just ask you in public or via PM.
Click to expand...

I didn't realize that this manual even existed until this thread. After a quick google search, I found this page with a bunch of scanned manuals for the Model III: http://www.1000bit.net/scheda.asp?id=112

Jason
 
Nice. Now I have two sets of files! For some reason, I wasn't able to find that web page. Perhaps I used the wrong search parameters.

For anyone curious (e.g. Terry) : The computer has not yet arrived. Maybe later this week.
 
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