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

[John T Chasteen]

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.
> >
> > --
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> >
> >
> >
> > 
>
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