[Coco] Hello, newbie with new toy

[Jerry Morelli]

Thanks for the tip Frank.  I actually already downloaded "Tandy's Little Wonder" a couple weeks ago (what a great reference!  good job!) as one of the first things to get me back on the path to CoCo-land.  That's where I read about the GIME chip maybe being the culprit.  My next order of business was going to be to reseat the RAM chips just for the heck of it, but there are capacitors (I think) by the end of each one that seem like they'll make it hard to pry the chips up properly.  I started on one by prying the opposite end but got nervous and stopped.

Your suspicion, and mine, is that the 6809 itself might be bad.  That's what I'm afraid of.  I'm already dealing with some other problems with my main PC and I just don't have a lot of time to mess with the CoCo.  I got it because "it's simple"  ;-).  Oh, you are right that the only socketed chips are the GIME and the RAM, at least in my case.

I also don't think I can get the "3 musketeers" screen when resetting.  Is that a CTRL-ALT-Reset that does that?  So my suspicion is a bad CPU, which is just my luck.

--- On Mon, 3/29/10, Frank Swygert <farna at att.net> wrote:

From: Frank Swygert <farna at att.net>
Subject: Re: [Coco] Hello, newbie with new toy
To: coco at maltedmedia.com
Date: Monday, March 29, 2010, 12:07 PM

Go to the archive site and download "Tandy's Little Wonder" -- farna section, TLW.pdf. I'm not saying this because I wrote it, but because there's a section in there on trouble shooting and repair that is geared toward those with noting more complicated than a multimeter. Actually I didn't "write" a lot of the book -- its' info gathered from many sources (and credited when known) compiled into one book. The repair section isn't all that technical, and covers all the easy stuff and a bit less than easy, but all easy to understand. The tech manual can be hard to follow unless you're really knowledgeable in electronics. 
The first thing I'd do is reseat every chip on the board in a socket though. The usually helps with intermittent problems. You already do that with the GIME, I seem to recall that on the CC3 the only other socketed chips are the memory chips. Worth a try! There's a gate that goes out to the cart slot that sometimes blows (someone else can point you there, I don't remember!), but if that's not it then the processor is probably bad. No buffer between processor and cart slot, so if someone did insert/remove a cart while the computer was on the CPU is probably bad. Most of the time they give garbage on the screen, but that's with a "hard blow". On rare occasion one doesn't blow all the way and gives symptoms similar to what you're experiencing. Most don't get that lucky.... if you want to call it that. Either way the CPU needs to be replaced.