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AuthorTopic: A500 with white screen, but boots fine  (Read 250 times)

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Offline JimDrew

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A500 with white screen, but boots fine
« on: July 04, 2022, 11:37:26 PM »
So, I have an OLD A500 (from my early development days) that when I power up connected to a 1084 I get the normal black->grey->white screen and then the floppy just clicks constantly looking for a disk - NO VIDEO.  The monitor and cable are confirmed working with an A3000 and A2000.  I also tried the composite video output from the A500 into several different monitors... just a white screen.  If I pop a disk into the drive it will boot whatever I throw in there and even the audio is working.. just no video.  The signal is good (HSYNC/VSYNC), just no video data.  I can even boot in PAL mode (mod to the Rev6A board) and I get the annoying PAL flicker on that I remember so well.... again, no video data!

I have replaced every chip except the FAT AGNUS (but it was cleaned and reseated).  I socketted and replaced the two 74HC245's that connect to DENISE.  I have not tried replacing the HYBRID VIDEO module yet - that is next.  This does have the 1MB CHIP mem upgrade with JP2 cut at the bottom and bridged at the top, and JP7 open.  Yes, this board use to work back in the day and except for video everything else seems to work.

I do not have a DiagROM (one is coming), but I don't think that is going to help debug this issue because it's just the video that seems to be bad - like the data bus to DENISE is faulty or maybe that HYBRID VIDEO module is faulty.

Any ideas?  Thanks!


« Last Edit: July 04, 2022, 11:39:28 PM by JimDrew »
 

Offline JimDrew

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Re: A500 with white screen, but boots fine
« Reply #1 on: July 05, 2022, 02:04:14 AM »
Just an update - I spent my 4th of July recapping this motherboard and now I get a pretty consistent green screen (sometimes the same white screen), so I am going to chuck this into a pile to work on some day!