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Model II vertical hold problem

D

dittman

Veteran Member
Joined
Jul 31, 2017
Messages
684
Location
Plano, TX
I have a Model II with the RCA CRT and CRT board. I had the AA11080 power supply in it and swapped it out for an AA11082. After that I have unstable vertical hold. Before I describe the symptoms I will say that I swapped back in the AA11080 power supply and it didn't help.

The symptoms are I can't get the video stable. It keeps rolling. I've tried adjusting the vertical hold on the CRT board and it doesn't help. I can get it to roll very slowly and even sometimes stop rolling for a bit but when it does the screen is is mid-roll with the top line about halfway down the screen. Adjusting the brightness and contrast controls on the front affect the vertical hold as well.

I thought maybe I had bumped something swapping out the power supplies (easy to do with the Model II) so I reseated all the connections on the CRT board and on the CRT. That didn't help.

Any ideas on where to look?
 
I suspect something was damaged on the analog video board when swapping out the PS. There's a lot of futzing around in that area to remove/install the PS board.
 
pski said:
I suspect something was damaged on the analog video board when swapping out the PS. There's a lot of futzing around in that area to remove/install the PS board.
Click to expand...

That's my worry as well.

If anyone has a spare board they want to sell let me know.
 
You can try adjusting the V-HOLD / H-HOLD which I assume are on the board. [edit: I see you tried that, sorry..]

You could try installing an auxiliary switching PSU. There's a thread about it somewhere that documents this and shows fitting a load resistor across the Tandy PSU 12v rail.

You could remove the CRT board and try replacing components around the v-hold circuit. Especially caps.

You may be able to use a small video mixer board to get a composite signal to feed a small LCD monitor that you could then fit inside the case. Like this one: http://www.cpcwiki.eu/forum/nc100-nc200-pcw-pda600/pcw-wont-start-anymore/msg165403/#msg165403 (and scroll down a bit).

Schematics and troubleshooting here: http://electrickery.xs4all.nl/comp/...ical_Reference_Manual_(1980)(Radio_Shack).pdf

Don't give up hope!
 
Last edited:
I've been thinking about a board to convert to composite to drive a monitor for a Model 12 motherboard from a smashed system. I can put the motherboard and power supply in a smaller case and use an external monitor and HxC for the floppies. It's on my (long) project list.

I'm thinking about just going ahead and recapping the board after TA18 and seeing if that helps.
 
I bought a Model III CRT board from Jay Newirth and installed it in my Model II and that fixed the video. As a bonus, the video looks better than it did a year ago when I first got the Model II.

Fortunately the Model III CRT board and the Model II CRT boards were the same for the RCA CRT.
 
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