[Coco] Troubleshooting CoCo 3

[Salvador Garcia]

Thanks Tom. Okay, that's a good idea. Salvador

      From: Tom Seagrove <tjseagrove at writeme.com>
 To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com> 
 Sent: Saturday, April 29, 2017 1:50 PM
 Subject: Re: [Coco] Troubleshooting CoCo 3
   
Try reseating the GIME Chip?  Cleaning its contacts?  Just another thing to try...

Tom

On Apr 29, 2017, at 1:39 PM, Salvador Garcia via Coco <coco at maltedmedia.com> wrote:

Hi all,
I finally got to start troubleshooting the CoCo 3 that HRietveld gave me. He suspected the power supply, so I started by following the flowchart that's on page 58 of the CoCo 3 tech manual. Almost everything checked out ok:
5v at tp1-13 at IC8 pin 15
I was not able to check the 8vdc at the output of IC36 because I was not able to locate any ICx larger than 19.
The CoCo came with 128K, but caps 65 and 66 were snipped, so I assumed that the previous owner at some time had a Triad 512K RAM expansion or similar product that required these caps to be snipped.
For testing I pulled the 128K and left the CoCo 3 "RAMless".
What sort of screen image should I get if I power up a RAMless CoCo 3?
If I pull the keyboard Mylar, what would the image on the screen look like?
Currently I am getting a "black" screen on power up.
Thanks! Salvador
PS: Full disclosure. The only tool I have (besides screw drivers and a soldering iron)  is a multimeter..

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