Intel MDS Series II IOC question

[Dave Mabry]

Joe R. wrote:

>At 12:27 AM 9/3/05 +0100, Tony wrote:
>  
>
>>>Greetings Dave,
>>>
>>>
>>>all say to replace the IOC if the 5 beeps test fails.  The manual called:
>>>      
>>>
>>Darn board-swapper guides...
>>
>>    
>>
>   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