[Coco] MPI problem or ...???
random_rodder at yahoo.com
Sat Jun 23 14:53:45 EDT 2007
The card edges are all clean, and I've cleaned the switch is good as I could (alcohol) for now. Jacksonville is the nearest town to me that has anything other than a Radio Shack to buy electronics supply stuff and cleaner from, unless I place an order with Jameco or Mouser.
Anyway, I used the 26-3124 manual for a little diagnostice last night, PEEKing at the value of 65407, and those all came back with the correct values for each slot. The next step was to start POKEing values into 65407 and then PEEKing them to see if the value was the same. So, I used the ones listed in the manual first, 0, 255, 85 & 170. The 0 & 85 came back fine, the 255 & 170 did not. So I poked some more values in looking for where the screw up begins. It begins with value 168, which returns 160 when PEEK'ed. Every value POKE'd into 65407 larger than 167 returns a number 8 less thanwhat was POKE'd.
I can't go any further in the process right now due to the MPI not even responding to the presence of a PAK being installed.Even a FDC still boots the the ECB screen. Any other pak, regardless of the slot it's in, causes it to boot only to a green screen.
----- Original Message ----
From: Gene Heskett <gene.heskett at verizon.net>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Thursday, June 21, 2007 11:41:30 PM
Subject: Re: [Coco] MPI problem or ...???
On Thursday 21 June 2007, Brian Blake wrote:
>Yes I do.
>Not having a service manual for this paricular unit I am currently thinking
> one of the IC's is bad, just had not gotten the scope out to look at any of
> the outputs. Just don't know where to start looking at this moment...
>Again, I haven't actually got the scope out to look, but, the DMM isn't
> picking up anything greater than .001vac. I'm not thinking that's enough to
> cause these problems, but, again, I've only recently got back to CoCoing...
>Thanks guys, keep the good info coming!!!!
>Brian (<- not an expert ;) )
A couple more things to check Brian since these things are nearly old enough
1. clean up all the blackened coating on the card edge connector that plugs
into the coco. Get brutal, as in a small piece of 0000 steel wool and some
contact cleaner & make it shine on both top and bottoom, and that includes
those 'ears' on each side as they are the main ground connection between the
coco and the mpi. Just don't power it up till all the steel wool has been
removed. That black stuff is just as good an insulator as that same black on
a battery post of your car battery. I got so tired of that that I sawed it
off, found a pc card with a gold plated finger pattern, and transplanted it.
That very tedious job was 15 years ago, and haven't had any problems with
2. If that mpi has not had the usual jumpering of all the card socket pin 8's
together, there is a probable problem there because the slot selection switch
has become oxidized and needs to be given a shot of cleaner and exercised.
Lots of exercise, then a couple more shots of contact cleaner.
Gene, a C.E.T.
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Sometimes, too long is too long.
- Joe Crowe
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