[Coco] Weird CoCo3 problem...

[Brian Blake]

Hi Mike,

1. Like the picture in the CoCo3 SM.

2. I thought of this about 2am this morning. Unfortunately, my second probe has grow a set of legs and walked away. Gotta order a new one.

3. Will do this tonight.

4. Will look at this tonight as well.



________________________________
From: Mike Pepe <lamune at doki-doki.net>
To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
Sent: Tue, January 5, 2010 12:04:24 AM
Subject: Re: [Coco] Weird CoCo3 problem...

Brian, looks good. I'd fire up my scope and show you some traces but it's currently sitting in pieces waiting for some parts. But, a couple of things to check:

1: what's your AC ripple look like on the 5V supply line?

2: You won't see the phase shift of the E and Q clock unless you're viewing both at the same time. The overshoot and ring apparent on the signals looks pretty bad but it could simply be the result of uncompensated probes.

3: run your poke loop and see what the SCS on the cartridge port looks like. It should be >2.5V most of the time with short blips <0.8V

4: if that looks normal, follow the schematic of the disk controller and see what the same signal looks like at pin 11 of the LS273 latch chip.

I'm thinking now that it could very well be possible that the cartridge connector is not completely contacting the pad on the disk controller edge connector and the SCS isn't getting into the cart.

> -----Original Message-----
> From: coco-bounces at maltedmedia.com [mailto:coco-
> bounces at maltedmedia.com] On Behalf Of Brian Blake
> Sent: Monday, January 04, 2010 8:23 PM
> To: CoCoList for Color Computer Enthusiasts
> Subject: Re: [Coco] Weird CoCo3 problem...
>
> 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
>
>