[Coco] MPI problem or ...???

[Brian Blake]

Well... I came home from work today expecting to take some voltage readings on the MPI. Was going to play some sinistaar first...

With all things powered up, it booted to ECB NOT DECB. Trying any other paks gets me a green screen with a single horizintal line tah blinks off anf on kinda scrolling up the screen. The results were the same regardless of the slot I used. Turn everything off, disconnect the MPI and plung in the FDC, boots right up to DECB, O-90 plays fine. So, I go ahead and check the volrage readings and all three are within .2v of the rated voltage, and the 5vdc line is perfect. Didn't get a chance to break out the O'scope, but. I figure this problem is beyond just being noise on the 5vdc line. Need to find a sercive manual for the 26-3024...

And to let you know how far the Shack has fallen I bought a brand new DMM (#22-812) back in February (RS-232 and all)... it died after the second reading. This thing has hardly been turned on since I bought it. I had to break out the old GB Instruments DMM to finish my readings...

Great night...

Brian

----- Original Message ----
From: Robert Gault <robert.gault at worldnet.att.net>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Wednesday, June 20, 2007 10:43:47 PM
Subject: Re: [Coco] MPI problem or ...???


Brian Blake wrote:
> Okay,
> 
> Had a little extra time so here's what I got from the PEEK:
> 
> 126
> 126
> 64
> 64
> 126
> 126
> 126
> 126
> 126
> 126
> 
> I got the same results with and without the MPI plugged in. I think the power supply is the issue. Late last night I woke up and heard a 'humming' sound. After stunbling around for a few minutes, I unplugged the MPI and it went away.
> 
> Anybody know if there's a service manual for this unit? It's a 26-3024...
> 
> Again, thanks for all the help,
> 
> Brian
> 
> 

Looks like the MPI is correctly modified for Coco3 use.

The humming probably is just slightly loose plates in the transformer 
and not a problem.

I'd suggest putting a VOM (or scope) on the MPI 5v line and seeing what 
happens as you add paks. If there is noise on the line or the voltage 
drops, you will have found the problem. If there is no change, more 
testing will be required to find the cause of the problem.

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