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Old 15 September 2018, 18:30   #1
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Amiga 2000 rev 6.2 - 2 colour bits missing


The colours of my 2000 are off. Stock 2000, rev 6.2

I wrote a testscreen program to see the issue better.

Normal brightness:


You can notice the last 3 colours are a bit too red

Same output, Low brightness:


The red is actually fine


But there is an issue with the 2nd bit of the green (so XX0X and XX1X are always exactly the same colour, like $010 and $030 for instance)


Same issue with the 3rd bit of the blue (not exactly obvious on the picture, but when paiting the screen with like $8 and $C confirm it's exactly the same shade)


I took the motherboard appart, I can't seem to see any fault (well, 3 fuses around the video output are gone & shorted, but the RGB signal fuses are still there)

The line drivers and the vidiot:


Denise herself:


Any idea what could be wrong ? Ever happened to anyone ?


Last edited by Clad; 17 September 2018 at 05:56.
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Old 11 October 2018, 23:31   #2
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After messing a bit with the Amiga (opened/closed it a few time, trying an accelerator board, then putting it back exactly the way it was) one, I got the 3rd bit of blue back for some reason. Does that help a diagnostic ?

Also, I changed Denise, no difference. (it's not what got the blue back)
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Old 11 October 2018, 23:45   #3
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Are you sure that the video cable and monitor work properly?
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Old 12 October 2018, 10:11   #4
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Yeah, I have plenty so it was one of my first try. Beside, a fault in the cable would not give a display like this one: https://drive.google.com/file/d/11dC...XWdFbMd5t/view

It's clearly an issue with one of the colour bit, but it's not denise.
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Old 12 October 2018, 13:31   #5
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Hmmm, there are a few things that deal with the colour in a bitwise fashion: there are logic buffer chips, pull-up resistors, and the video hybrid itself that could all be at fault. Also, check for debris or corrosion around the video slot - shorts here will cause bits to go missing on the analogue output. Given the temperamental nature of the fault, I would expect it's some cracked joints somewhere along the way, and the bending of the board from the troubleshooting has moved something enough to give good contact again.
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