[Coco] F board video issues

[Zippster]

Hi Josh,

See below…

- Ed



> On Apr 20, 2015, at 1:55 AM, Josh Harper via Coco <coco at maltedmedia.com> 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

This could be the 6847 having trouble accessing it’s internal character ROM, especially if the missing parts
of letters are horizontal scan line portions of the letters.  Try reseating the MC6847, if that doesn’t work, try swapping
it with a known good one.

> 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

The reddish screen is likely a problem in the MC6847, MC1372, and RF modulator box chain.

Considering the OK promt as well, pull and reseat all socketed chips in the machine if you haven’t  already.
Then I’d try swapping the MC6847 & MC1372 (one at a time) with known good ones.  If that fails, I’d suspect
the modulator box.

> also I have a hjl keyboard that when u press ? it gives you a = ? instead theres a few other keys that do this,its all so using a keyboard adapter,, I tried a different keyboard and it worked fine

On this I would disassemble the keyboard, check all electrical contacts, and give them a good cleaning with 91% iso.

> does anyone how I might fix these problems
> thanks for ur help
> 
>