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

[Brian Blake]

Okay some more testing done...

I changed around the devices and the slot number the switch is set to and got the same results. Then I took everything except the FD-502 and also plugged Mega_Bug into slot 1, with the switch set to 4, and it booted to DECB 1.1. Turned everyrthing off and put the switch on slot 1 and Mega-Bug started fine. The only pak that seems to allow proper booting is the SS/C.

I opened up the case, and there has been a mod that looks like a PAL upgrade. I did loosen up the transistor, made sure there was no oxidation and re-tightened it. The big cap looks fine, no swelling or leaking visible. I didn't take the board all the way off and check all of thw solder joints, figured I'd do that next weekend. In the mean time, any other suggestions?

Thanks for the help guys,

Brian



----- Original Message ----
From: Brian Blake <random_rodder at yahoo.com>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Tuesday, June 19, 2007 11:43:50 AM
Subject: Re: [Coco] MPI problem or ...???


Mark and Robert,

Thanks for your replies. I will look for both of these problems tonight. 


Thanks again,

Brian




----- Original Message ----
From: Mark Marlette <mark at cloud9tech.com>
To: coco at maltedmedia.com
Sent: Tuesday, June 19, 2007 11:13:52 AM
Subject: Re: [Coco] MPI problem or ...???


There is also a large electrolytic cap that after 10-20 years might be  
a bit dry.......

Mark
Cloud-9

Quoting Robert Gault <robert.gault at worldnet.att.net>:

> Brian Blake wrote:
>
>> Greetings all. I ran into a problem with my MPI this weekend.
>> <snip>
>> Then, I tried another 512k CoCo 3. First, with just the FD-502 and
>> everything works fine. Next, the MPI and FD-502 in slot 4, everything
>> worked. Then the SS/C in slot 3, everything works fine. Next up was
>> with the O-90 in slot 2. Not fine... I noticed immediately that it was
>> booting to DECB 1.1 instead of 2.1. ><snip>
>
>  This type of problem looks like a power supply defect in the MPI. Load
> up enough devices and the MPI flakes out.
>  A good test for this is to change the order of paks and their
> positions in the MPI. For example, what happens with an MPI, a disk
> controller in slot1, the ORC-90 pak in slot4, and the MPI switch at
> slot1? If the Coco will power up in DOS 2.1, the problem is not with
> the ORC-90 pak. It will either be a non-modified MPI or power supply
> problem.
>  A test of modified vs non-modified, is to start a Coco3 without an MPI
> and PEEK $FF90-$FF99, see what the values are, plug in the MPI and see
> if the values change. If the values change, the MPI most likely is not
> modified for Coco3 use.
>  Power supply failure normally is a loose or oxidized contact on the
> main power transistor. This is caused by a screw making a bad contact
> with the transistor case. Loosen the screw/lock washer and re-tighten
> it. That should improve the situation.
>
> --
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco



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