27 May
2003
27 May
'03
7:49 p.m.
In message <m19Kn8R-000IznC@p850ug1>
ard(a)p850ug1.demon.co.uk (Tony Duell) wrote:
I know...
I also know that the repairs to the through-hole plating for the main RAMs,
buffers and video RAMs are fine.
That leaves the possibility of:
A) Dead RAMs
B) Dead LS buffers
C) Dead ROMs
I can pretty much discount C - the ROMs work fine in my Preprom - even at
4.5V (it's a so-called "Production Grade" programmer - the multilevel verify
can be disabled, though).
*still*
won't boot to the FORTH interpreter.
Argh!. There aren't that many chips in
the machine... Garbage as in random dot patterns, or garbage as in
characters? Is it
loading the character generator at all?
Random dot patterns. It doesn't look
like the chargen is getting loaded at
all.
Where are you in the country? I am not lending out any
of my test gear (I
depend on it too much!), but if it's physcially possible for us to get
close together, I can have a quick look and wave some probes over it...
I'm in
Leeds, West Yorkshire.
I believe the normal ROMs do that early on anyway....
I've never heard of
a diagnostic ROM for the ACE
They load the chargen *after* testing the main RAM. If
the main RAM test (or
another part of the POST) fails, the Ace won't even load the chargen. If I
had designed the firmware, I'd have made it load the CG RAM, clear the VRAM
and then run a selftest. If the selftest fails, display an error. Simple.
Instead, I get the dubious pleasure of re-learning Z80 assembler and hacking
together a diagnostic ROM...
I'll try monitoring the RAMSEL, etc. pins on the LS138. I think there's a
bus conflict somewhere because the CPU, EPROMs and RAMs are getting quite
hot... I'll try and track down a thermometer later. I know there's a
DS18S20 DirectDigital sensor around here *somewhere*...
Later.
--
Phil.
philpem(a)dsl.pipex.com
http://www.philpem.dsl.pipex.com/