[Coco] F board video issues

[Rogelio Perea]

On Mon Apr 20 2015, Josh Harper wrote:

 I have 3 coco 1 F boards with video issues
> 2 of them show up with the normal boot screen  but the writing  is missing
> parts of the letters almost looks faded  example there is part of  a Y  or
> half a O and so on
> the 3rd coco 1 will boot to a normal boot screen except  instead of green
> its redish
> and some times it will just boot to a ok prompt only,,with the same redish
> screen


I also have a Samsung monitor (17" or so) ant it does a poor job rendering
the analog TV from any CoCo I hook up to it. Still, it displays a decent
32x16 text screen. Few days ago I repaired one F board CoCo 1 that had bad
video output: sometimes the image would tear on the edges making all
characters there blurry, sometimes it would power up in B&W and if I
flipped the channel switch sometimes I would go worse. After checking clock
signals at the SAM, the VDG and Video modulator (MC1372) I replaced the
later (it's a 14 pin chip - top upper right of the RFI cage), next power up
I had a beautiful VDG screen back - as good as the Samsung can push that is.

Check that MC1372 chip, first try reseating it - would not hurt to do the
same to any other socketed chip. If reseating does not work, replace. I got
the spare 1372 on Ebay.


-- RP