[Coco] Grr!!! Bad MPI! No biscuit!

[Gene Heskett]

On Saturday 05 May 2007, Joel Ewy wrote:
>Jim Cox wrote:
>> I have a MPI board that someone gave me.  I am not sure if it works or
>> not, but it's yours.
>>
>> Jim
>> PS: We need a new MPI for the CoCo
>
>Here's a humble suggestion for anyone contemplating such a thing:
>Orient the board perpendicular to the desktop so that any cartridges
>plugged into it will be parallel with the desktop.  Having the disk
>controller stick up 8.5" from the surface of the desk is just a bit silly.
>
>As much as I loathe trying to find places to plug them all in, maybe an
>external transformer would be a good idea here.  That way, if people
>were building one into a (mini) tower case they could just leave that
>bulk out and plug straight into the PC power supply.  Could be a "floor
>wart" that runs another cord from the transformer to the wall.  Used
>30VDC ones from old DeskJets seem to be plentiful around here.  Would
>that be too much to regulate down to 12V with a 7812?

It needs all 3 voltages, +5, and + and - 12.  I cut all that away years ago, 
and both my coco3 and the mpi as well as all my drives run on an old AT style 
psu.  NO detectable heat anyplace except on top of a drive eventually.

>Would it be feasible to put bi-directional bus drivers in a short
>cartridge and connect the CoCo to the MPI via a short length of ribbon
>cable?  That would provide much greater flexibility in placement, and
>probably reduce the chances of bumping things out of place.
>
>JCE

This idea falls over due to a bus contention in the mpi's internal timing, 
which in turn causes a ground bounce that is only barely tolerable if the 
grounding ear clips in the side port have a good clean grip on the mpi's 
ground plane.  Additional jumpers of heavy wire to tie the mpi's rather 
surpentine ground plane together also help, as does additional bypassing near 
the ls245.  You can make it stable, as shipped, its a house of cards.
 
>> On Sat, 5 May 2007 03:12:01 -0600
>>
>>  Willard Goosey <goosey at virgo.sdc.org> wrote:
>>> My old-style MPI is apparently toast.  My CoCo has therefore lost
>>> access to its hard drive.  :-(
>>>
>>> I suspect power supply problems.  Either that or the upgrade PAL is
>>> loosing its mind.
>>>
>>> Just what I need, something else broken.
>>> Willard
>>> --
>>> Willard Goosey  goosey at sdc.org
>>> Socorro, New Mexico, USA
>>> "I've never been to Contempt!  Isn't that somewhere in New Mexico?"
>>>   --- Yacko
>>>
>>> --
>>> Coco mailing list
>>> Coco at maltedmedia.com
>>> http://five.pairlist.net/mailman/listinfo/coco
>>
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>
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-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
This fortune is dedicated to your mother, without whose invaluable assistance
last night would never have been possible.