[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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> 

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