[Coco] Erratic MPI Behavior

[Robert Gault]

Boisy G. Pitre wrote:
> Folks,
> 
> I have a 26-3124 MPI, upgraded for the CoCo 3, that behaves in the 
> following manner:
> 
> 90% of the time, with a working disk controller and DOS in slot 4 and 
> the switch at that position, the CoCo 3 fires up in ECB, not Disk BASIC. 
> If I turn the CoCo and MPI off and on enough times, it will eventually 
> fire up into Disk BASIC, but a power cycle usually results in the ECB 
> screen again.
> 
> This is a major annoyance.  Another MPI of the same model, also 
> upgraded, works consistently in place of this one.  Something is wrong 
> with this Multi-Pak.
> 
> I've scrubbed both sides of the card edge connector with an eraser 
> thinking that dirty leads might be the cause.  Still, the same behavior 
> persists.
> 
> Does anyone have any possible ideas on what this might be?
> 
> Boisy
> 
> 

The main power transistor in the MPI is tied by two nuts with lock 
washers to the circuit board. These connections can oxidize after which 
there won't be power on the MPI. My MPI was "repaired" after I loosened 
and re-tightened these screws with a socket wrench. Take care not to 
over tighten.