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

Thu Jun 21 22:39:59 EDT 2007

John,

Yes I do. 

Not having a service manual for this paricular unit I am currently thinking one of the IC's is bad, just had not gotten the scope out to look at any of the outputs. Just don't know where to start looking at this moment...

George,

Again, I haven't actually got the scope out to look, but, the DMM isn't picking up anything greater than .001vac. I'm not thinking that's enough to cause these problems, but, again, I've only recently got back to CoCoing...

Thanks guys, keep the good info coming!!!! 

Brian  (<- not an expert ;) )

----- Original Message ----
From: John T Chasteen <johnchasteen.2 at juno.com>
To: coco at maltedmedia.com
Sent: Thursday, June 21, 2007 10:21:08 PM
Subject: Re: [Coco] MPI problem or ...???

Brian do you check the voltages while the load is applied?

John

On Thu, 21 Jun 2007 21:12:36 -0500 "George's Coco Address"
<yahoo at dvdplayersonly.com> writes:
> 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.
> >
> > --
> > Coco mailing list
> > Coco at maltedmedia.com
> > http://five.pairlist.net/mailman/listinfo/coco
> >
> >
> >
> > 
>
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> > 
> 
> 
> 
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> 
> 

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