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Some issues with a coco 1.


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I recently acquired a couple CoCo 1s. One of them, a beige 64k, has a few issues. I am very new to retro computers, so I am nearly clueless here.


1. Video issues

when I turned it on this morning, the video signal was nearly gone. It’s been going downhill for some time now, and I think interference has something to do with it, but I can’t know. It was just artifacts first, but it degraded to the black and white you see in the image. It does occasionally switch back to color image.


2. Floppy disk controller card problems


when I insert either of my 2 floppy controller cards, an official and unofficial one, they give a strange checkerboard pattern with characters, which based on the little I’ve found, means about anything can be wrong. Normal cards work. I heard this can mean a weak power supply, so I checked pin 1 and 2 on the card slot and got 23v, which, if I’m not mistaken, DEFINITELY should not be there. The second machine I’m using as a parts donor, so I have a few replacement chips. I do not have an oscilloscope, so I can’t check anything like that. Anything I can do?



Edited by 3pic
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Yes, capacitors were the culprit for my Coco I, once I replaced them the video noise reduced considerably.  With RF it will never go away, but you can get it to be usable.  Best solution is to do a composite modification. 


About the disk controller, I don't know, I don't have one and I'm not too familiar with these computers.

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  • 3 weeks later...

On the CoCo1 pin 1 is the -12VDC output and pin 2 is the +12VDC output, so 23VDC is pretty close.  You could check the voltage between ground, pins 33 and 34, and +5VDC, pin 9.  You should check both DC and AC.  The DC should be about 5 volts, probably slightly more, and the AC should be negligible. 


That first picture looks like something I've seen before on several different game consoles and computers.  It can be caused by a bad RF switch, or just dirty contacts in same.  Also, the channel switch might be in the wrong position.  Make sure you have the TV and the computer on the same channel.  The channel switch inside the CoCo might be bad or dirty so switch it back and forth(wiping the contacts) a few times to see if it makes a difference.  Try using channel 4(assuming you are on channel 3).


Since regular cartridges work, the second picture makes me think your disk controllers are made for CoCo2 or CoCo3.  Is that possible?  Pins 1 and 2 are grounds on the CoCo2.  In that case the controller might be receiving a ground where it requires -12 and +12 VDC.  They are supposed to be no connection on the CoCo3.  If you give the model #'s on those controllers someone on this site might be able to tell you whether they are compatible with the CoCo1.



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