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Thread: Model II vertical hold problem

  1. #1

    Default Model II vertical hold problem

    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?

  2. #2
    Join Date
    Feb 2014
    Location
    Netherlands
    Posts
    409

    Default

    Check the 12 volt on the new power supply.
    Check if all ground cables are connected.

  3. #3

    Default

    I've verified 12V is good.

    The grounds all show continuity on the cables.

  4. #4

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    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.

  5. #5

    Default

    Quote Originally Posted by pski View Post
    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.
    That's my worry as well.

    If anyone has a spare board they want to sell let me know.

  6. #6

    Default

    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-nc...403/#msg165403 (and scroll down a bit).

    Schematics and troubleshooting here: http://electrickery.xs4all.nl/comp/t...dio_Shack).pdf

    Don't give up hope!
    Last edited by JonB; November 1st, 2018 at 10:47 AM.

  7. #7

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    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.

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