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

[George's Coco Address]

Brian,

  Don't forget to check for AC content in the DC voltages. This will check 
for bad caps.

George

----- Original Message ----- 
From: "Brian Blake" <random_rodder at yahoo.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Thursday, June 21, 2007 8:56 PM
Subject: Re: [Coco] MPI problem or ...???


> 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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