[Coco] Weird CoCo3 problem...

Sat Jan 2 00:08:19 EST 2010

Hi Mike,

Here's what I did - not sure if it was correct:

10 POKE &HFF40,1
20 GOTO 10
RUN

I then checked pin 6 of IC9 - which according to my schematic is the /SCS line - HI reading on my DMM in logic mode (<1 = LO, >2 = HI, in between it shows the voltage).
I then checked pin 40 on the 6809 - the /HALT line - and got a reading of 1.545vdc.
Not sure if my DMM would react fast enough, I changed to Frequency mode and checked pin 6 of IC9 again - got a reading of about 15-kHz.
I hit the break key and checked pin 6 again, and it was still HI.
Shut of the CoCo, waited a few seconds and turned it back on, checked again and it was still HI.
Checking pin 36 on the slot yielded similar results, except the frequency was very different ~110-kHz.

________________________________
From: Mike Pepe <lamune at doki-doki.net>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Fri, January 1, 2010 9:45:14 PM
Subject: Re: [Coco] Weird CoCo3 problem...

I'd put that POKE &HFF40,1 into an endless loop and look to see if the SCS line on the cartridge port is stuck high or if it pulsates.

Radio Shack used to sell a pretty decent logic probe for about $20. Not sure if they still do, but it would help diagnose the problem in this case.

The latch at $FF40 should function independently of a blown out 6809 HALT line which is what usually indicates a CPU replacement.

> -----Original Message-----
> From: coco-bounces at maltedmedia.com [mailto:coco-
> bounces at maltedmedia.com] On Behalf Of Brian Blake
> Sent: Friday, January 01, 2010 4:48 PM
> To: CoCoList for Color Computer Enthusiasts
> Subject: Re: [Coco] Weird CoCo3 problem...
> 
> Nope - no logic probe. What kind of signal should be seen there? My DMM
> has some logic functions built into it, but, I'm not sure off hand what
> it's capable of...
> 
> 
> 
> ________________________________
> From: Mike Pepe <lamune at doki-doki.net>
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> Sent: Fri, January 1, 2010 7:39:58 PM
> Subject: Re: [Coco] Weird CoCo3 problem...
> 
> That's pretty strange. If you have a logic probe you can do some more
> investigation. The LS138 chip may be faulty.
> 
> > -----Original Message-----
> > From: coco-bounces at maltedmedia.com [mailto:coco-
> > bounces at maltedmedia.com] Ong happens accept an I/O error - not light,
> no
> > disk activity, nothing...
> >
> >  Behalf Of Brian Blake
> > Sent: Friday, January 01, 2010 3:24 PM
> > To: CoCoList for Color Computer Enthusiasts
> > Subject: Re: [Coco] Weird CoCo3 problem...
> >
> > Tried the POKE and no drive activity light came on. Anytime I try to
> > access the disk, nothin
> >
> > ________________________________
> > From: Mike Pepe <lamune at doki-doki.net>
> > To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> > Sent: Fri, January 1, 2010 6:08:28 PM
> > Subject: Re: [Coco] Weird CoCo3 problem...
> >
> > I suspect the 6809 as well. But if you do a poke &HFF40,1 the drive 1
> > activity light should go on. If not something else may be wrong.
> >
> > > -----Original Message-----
> > > From: coco-bounces at maltedmedia.com [mailto:coco-
> > > bounces at maltedmedia.com] On Behalf Of Brian Blake
> > > Sent: Friday, January 01, 2010 2:36 PM
> > > To: CoCoList for Color Computer Enthusiasts
> > > Subject: Re: [Coco] Weird CoCo3 problem...
> > >
> > > Hi Arthur,
> > >
> > > Unfortunately, it's not socketed. Tho, I have about 9 6309's and
> > plenty
> > > of sockets... hmmmm.... maybe tomorrow....
> > >
> > >
> > >
> > > ________________________________
> > > From: Arthur Flexser <flexser at fiu.edu>
> > > To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> > > Sent: Fri, January 1, 2010 3:56:15 PM
> > > Subject: Re: [Coco] Weird CoCo3 problem...
> > >
> > > I vaguely recall something like this happening to me years ago that
> > was
> > > fixed by replacing the 6809.  If this machine and one of your
> others
> > > has had
> > > the 6809 socketed, it would be easy enough to swap in a 6809 from
> one
> > > of the
> > > other machines and see if the problem goes away.
> > >
> > > Art
> > >
> > > On 1/1/10, Brian Blake <random_rodder at yahoo.com> wrote:
> > > >
> > > >
> > > >
> > > > All of these new developments on the CoCo front finally lit the
> > fire
> > > under
> > > > my arse to set up real hardware again. Besides my repack project,
> I
> > > have 3
> > > > other CoCo3's, two with 512k upgrades (one C9 and one PBJ) and
> one
> > > 128k. The
> > > > one with the C9 upgrade works fine - can load and play
> Sockmaster's
> > > Donkey
> > > > Kong.
> > > >
> > > > The one with the PBJ upgrade, not so... At boot, it comes up as
> it
> > > should
> > > > with the proper display. However, any floppy commands are met
> with
> > no
> > > > response from the floppy drive (with an FD-502 controller) at
> all.
> > > Almost
> > > > like the drive is off. The drive responds as it should in the
> other
> > > two
> > > > machines. Upon removing the top case and k/b, I saw two wires,
> each
> > > had been
> > > > soldered to opposite sides of R23. Now, under the keyboard, is
> > > another wire
> > > > with alligator clips on each end, and the clips are holding on to
> > the
> > > bare
> > > > end of the wires soldered to R23, effectively bypassing the
> > resistor.
> > > I'm
> > > > looking for the PBJ instructions, pretty sure I have them, to
> find
> > > out if
> > > > this is called for. I can also see where C65 & C66 have been cut
> > and
> > > > re-soldered. I have reseated the GIME and the PBJ memory chips,
> and
> > > cleaned
> > > > the 40 pin connector.
> > > >
> > > > Any other suggestions? My 100MHz o'scope bit the dust so I don't
> > have
> > > that
> > > > tool any more (anybody have a CRT for a Leader 3 channel 100MHz
> > > scope??)
> > > >
> > > >
> > > > Thanks,
> > > >
> > > > Brian
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Coco mailing list
> > > > Coco at maltedmedia.com
> > > > http://five.pairlist.net/mailman/listinfo/coco
> > > >
> > >
> > > --
> > > Coco mailing list
> > > Coco at maltedmedia.com
> > > http://five.pairlist.net/mailman/listinfo/coco
> > >
> > >
> > >
> > >
> > >
> > > --
> > > Coco mailing list
> > > Coco at maltedmedia.com
> > > http://five.pairlist.net/mailman/listinfo/coco
> >
> >
> > --
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> >
> >
> >
> >
> >
> > --
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> > Coco at maltedmedia.com
> > http://five.pairlist.net/mailman/listinfo/coco
> 
> 
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> 
> 
> 
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