Re: Totally OT, but I thought I'd ask anyway...

[Nama <forums6000@mac.com>]

On Jun 16, 9:53 am, Alex Freed <alex_n...@mirrow.com> wrote:
> Nama wrote:
> > However one problem still persists. The characters on screen seem to repeat themselves every 8
> > characters!
>
> > Anyway, I was hoping that someone here may know what would cause this.
>
> The problem is most likely with the address lines for the video memory.
> I know nothing about this particular computer, but it looks like the
> memory itself is OK as the CPU works. There must be some circuit driving
> the video. Find the wire going to address 3 and see if it is cut or shorted.
> Oh, as the board uses DRAM there will be no address 3 pin on the memory
> itself. There will be a multiplexer chip somewhere i.e. 74LS157 or similar.
>
> If you don't know what I'm talking about you can only try to visually
> find yet another broken or shorted wire.
>
> -Alex.


] 3ob, thanks for the pointer to that forum, I'll check it out...

but first I'll try Alex's suggestions.

Just curious, Why address line 3?
I believe there are three LS157's connected to two 2114 ram. This RAM
is then connected to the character ROM, which in-turn connects to the
video generator circuit.
I'll have a probe around these LS157's when I get home tonight.

Thanks, and I'll let you know what I find.

Philip