[Coco] Weird CoCo3 problem...

Brian Blake random_rodder at yahoo.com
Mon Jan 4 23:23:19 EST 2010 

Okay guys, got the o'scope, schematic and CoCo3 service manual, along with Frank's 'Tandy's Little Wonder' out for good measure and started reading and testing. The results have been posted to my blog at the following address so I could post pictures of the actual scope traces.

http://cocom3repack.blogspot.com/2010/01/troubleshooting-perplexing-problem.html

I'm not sure if these will be much help or not, as the test results are... interesting. I've got the exact same signal from the GIME to places I wouldn't think they should be (i.e.: GIME output to TP2, 3, 4 & 5 appears to be identical, and NOT what the service manual says they should be). I freely admit there are folks here who have forgotten more than I know about the CoCo family, so I hope these images help.


Thanks guys,

Brian


________________________________
From: Mike Pepe <lamune at doki-doki.net>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Mon, January 4, 2010 11:39:49 AM
Subject: Re: [Coco] Weird CoCo3 problem...

You know, I was also thinking that maybe a bad power supply could be to blame here.

My spam filter got screwed up, I think I missed some list messages. Any updates on this issue?

> -----Original Message-----
> From: coco-bounces at maltedmedia.com [mailto:coco-
> bounces at maltedmedia.com] On Behalf Of Mike Pepe
> Sent: Saturday, January 02, 2010 9:35 AM
> To: CoCoList for Color Computer Enthusiasts
> Subject: Re: [Coco] Weird CoCo3 problem...
> 
> I've never seen this particular issue before, but from what you describe the
> only thing I can think of is the SCS signal is not making it into the cartridge
> itself. I wonder if a different I/O pak such as the RS232 pak is functional on
> this system or not.
> 
> 
> 
> 
> > -----Original Message-----
> > From: coco-bounces at maltedmedia.com [mailto:coco-
> > bounces at maltedmedia.com] On Behalf Of Brian Blake
> > Sent: Saturday, January 02, 2010 6:05 AM
> > To: CoCoList for Color Computer Enthusiasts
> > Subject: Re: [Coco] Weird CoCo3 problem...
> >
> > Hi Mike,
> > The answer to both of those is 'yes'.
> >
> > I tried Tetris and it worked fine.
> > I also tried the POKE on the CoCo3 with the C9 512k upgrade and the
> > Drive 0 light did come on.
> > --- On Sat, 1/2/10, Mike Pepe <lamune at doki-doki.net> wrote:
> >
> > From: Mike Pepe <lamune at doki-doki.net>
> > Subject: Re: [Coco] Weird CoCo3 problem...
> > To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
> > Date: Saturday, January 2, 2010, 2:10 AM
> >
> > 15KHz sounds about right for a loop like that. Every poke to that
> > address should drive SCS low momentarily.
> >
> > Two other things come to mind for checking- if you put this
> > controller/drive on another machine, does the poke make the drive
> > activity light come on? Second thing is- do any other cartridges work
> > on this machine? Any game paks to test with?
> >
> >
> > > -----Original Message-----
> > > From: coco-bounces at maltedmedia.com [mailto:coco-
> > > bounces at maltedmedia.com] On Behalf Of Brian Blake
> > > Sent: Friday, January 01, 2010 9:08 PM
> > > To: CoCoList for Color Computer Enthusiasts
> > > Subject: Re: [Coco] Weird CoCo3 problem...
> > >
> > > 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
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > >
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