Dragon 64 fixing...

From: Jules Richardson <julesrichardsonuk_at_yahoo.co.uk>
Date: Mon Jul 19 10:29:07 2004

Finally found the five minutes to see if my Dragon 64 works. It doesn't.

I get a white screen with a black border (which seems healthy enough),
then in the centre of the screen a few random characters (some with
inverse video). Occasionally after a reset the random characters don't
stay together but occupy random locations toward the middle of the
screen.

I assume (having never seen an operational D32 or 64 before) that it
should say "Dragon 64" or something, implying that character generation
is screwed - but why the random characters should jump positions
sometimes I don't know (unless the design of the reset circuitry is not
very good)

One obvious fault I found was that pin 6 of the 40 pin 6847 IC was
broken and had been badly repaired in the past (such that I don't think
the joint had held), but fixing that hasn't made a difference. The fact
it was ever broken at all suggests that someone's been fiddling inside
the machine though...

I notice IC17 (a socketed 18 pin DIL) is missing - should it be?

None of the DRAM is getting warm (suggesting failure), and the fact that
there's something approaching normality on the display suggest that the
power rails are OK and the CPU's at least operating.

Of course presumably a RAM fault could quite easily explain random
characters and locations though, but doesn't explain the stable white
screen / black border (unless that's done in low level video hardware).

Any ideas? If I can get this thing running then it's another potential
for the CGE show this coming weekend.

cheers,

Jules
Received on Mon Jul 19 2004 - 10:29:07 BST