Tony wrote:
> Good! If you have the disk controller in the system (read : If you have
> the Expansion Interface connected), then the machine tries to boot the
> disk _before clearing the screen_. If you don't have a disk in the drive,
> then you get a screen of garbage.
<snip good advice>
I should've said that because the previous owner showed me the machine gave
a garbage screen I didn't bother getting anything other than the machine and
monitor out of their boxes - no point testing the rest when the machine
won't even power up correctly :)
So far I've got the problem down to probably bad address/data lines at the
ROMs. I found a link to the Tech Ref for the Model 1 - excellent book, given
the writing style it could've been written by me, same sense of humour - and
the 'remove and test' method leads me down the bad ROM path - without the
ROMs in the machine I get a screenful of _at_9, which indicates the CPU and
video RAM are happy.
Next task is to go thru the address lines with a probe; grounding the TEST*
line on the CPU makes the ROMs tri-state so I should be able to see any bad
lines that are (according to the tech ref) 'floating' instead of
'tri-stating'. Some good bed-time reading to be had there :)
> > of the machine I'd take a stab at bad RAM since both my PET
> 2001 and UK101s
> > had that problem and both were fixed by new video RAM.
>
> The M1 doesn't use 2114s :-)
This I now know.....good job the tests indicate the RAM is happy! I guessed
when the RAM turned out to be 16 pin chips instead of the 2114's 18.....
(I'll start work on dismantling the MIII's PSU on monday, Tony :))
cheers
--
adrian/witchy
www.binarydinosaurs.co.uk - the online computer museum
www.snakebiteandblack.co.uk - monthly gothic shenanigans
Received on Mon Feb 17 2003 - 02:09:10 GMT