[Coco] Troubleshooting CoCo 3

[Christopher R. Hawks]

On Sat, 29 Apr 2017 17:39:34 +0000 (UTC)
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..
> 

Salvador:

    IC36 is the 8 volt regulator near the RF Modulator on the
schematic. (Right under the word SCHEMATIC in fact.)



Christopher R. Hawks
HAWKSoft
-- 
To gain the friendship of a cat is not an easy thing.  It is...a
creature of habit and a lover of order and cleanliness.  It will
consent to be your friend if you are worthy of the honor, but it will
not be your slave. -- Theophile Gautier
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