Fixing a Newbrain – Problem with the video

[CDesp]

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I am trying to resurrect a Newbrain and currently it has two problems. One is with the memory cause it sees only 5kb and if i swap the two 16kb banks it does not boot so the second is no good at all.

The current problem i am wroking is the video. In text mode it seems out of sync but when i open a graphics screen everything works ok.

I think the problem is the end of text screen circuit but i can’t seem to find it on the schematics.

You can see a small video of the problem here https://youtu.be/eUgqRaY9VpA

 

 

• This topic was modified 7 months, 3 weeks ago by CDesp.

[CDesp]

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I finally fixed it. It was the FRM signal it didn’t propagate from IC 451 Pin 4 to IC 419 on Storage Board Pin 5. I thought that since the graphics worked it should be an IC that has the ~GR signal in the inputs and that one is the 419 on Storage Board, it is an AND with ~GR and FRM as inputs so from there it was easy to trace the problem.

I traced it from Pin5 right under the cop420 ic419 on MB but then i couldn’t see where the problem was so i soldered a small jumper cable between IC451 Pin 4 and the via under the Cop and filckering went away.

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