3 Sep
2005
3 Sep
'05
1:19 p.m.
Joe R. wrote:
At 12:27 AM 9/3/05 +0100, Tony wrote:
But if they didn't tell you that then haven't to tell you how to fix
the
IOC board and provide schematics, etc. So telling you to replace the board
is an easy out for the manufacturer. Plus selling you a new board makes
them $$$.
Joe
Now Joe,
Don't be so cynical! ;)
You know that Intel provided some of the best documentation of anyone in
those days. I just don't happen to have the right manual that describes
that diagnostic. I believe it existed but was mainly for the repair
techs. I have lots of good docs, as you well know, and as you do also,
but it seems that we might both be lacking the particular one I need.
I was able to get in touch with one of my old buddies who was an Intel
repair tech. He said that at one time he had the source code for the
firmware in that IOC board. Boy! I would like to have a copy of that,
but he didn't keep it and is retired. Unlike me, he HAS a life and
enjoys other things, so he got a kick out of my struggles with this IOC.
BTW, I have managed to disassemble a good portion of the 1.3 version of
the firmware (not the newest, but something that I started disassembling
many years ago) and figured out some of the beep codes.
Beep 1 and Beep 2 happen after checksumming the EPROMs.
The pause next is a RAM test. It has 2108's, eight of them, so that
is...a whopping 8k bytes I think! It takes a 2.4MHz 8080 a little time
to cycle through them.
The third beep signifies that the RAM test was successful.
Next is still kind of fuzzy. It looks like it starts using a real
stack, since the ram is good, and then initializes the CRT controller
chip. It looks like it needs to see some kind of status returned from
it to continue. There are at least three places that it can halt before
the next beep, and the 8275 CRT controller is one of them.
So that may be my problem. Now I'm looking for an 8275 chip. Can't
find one just yet, but I just started looking. I might have to disect a
working MDS to swap some chips.
BTW, the one white MDS I got from you that didn't work...well, the IOC
was totally dead on it. Based on this work on the disassembly I
determined that the first beep can also fail to happen if the 8253
counter/timer chip isn't working. That is one of the signals that gates
the beeper "on". I replaced that chip on the IOC from that machine and
now it gives me three beeps, just like the one that started this whole
journey. Interesting, at least to a nerd like me.
Well, more to come, I hope. What a way to spend a long holiday
weekend! At least it doesn't cost me any gasoline to do this!!!
Take care, and I'll keep the list posted if there is anyone interested.
Dave
Greetings
Dave,
all say to replace the IOC if the 5 beeps test fails. The manual called:
Darn board-swapper guides...