[Coco] Rebuild and/or modifications for Multi-pak?

John E. Malmberg wb8tyw at qsl.net
Sun Jun 14 10:14:10 EDT 2020

I have an original multi-pak that arrived DOA from E-bay.

The schematic and circuit board look simple enough for me to eventually 

I have seem some discussions here in the past about weaknesses in the 
design, particularly signal noise.

So looking for advice on what to do for the repair, which would include 
a PAL upgrade.

A. Replace with original 74ls parts.

B. Upgrade to a newer compatible parts like 74ALS family parts, etc.

C. Additional circuit mods to improve reliability?

I see reports of COCOs being blown from the 12V signal from the MPI 
hitting the COCO if the MPI moved while both devices are powered up.

Is there any reason to have the 12 power being fed back to the COCO?
It seems like just cutting that trace would be of help.

How long could I extend the 40 pin BUS to add additional slots and what 
are the gotchas.  It appears that I have been able to get away with 
adding 3 slots with just a ribbon cable in the past.

Not sure what to use for ground connectors for the additional slots.


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