Amiga 1200 2B Mainboard - Data bus high

highpuff

Active member
Joined
Oct 10, 2012
Posts
647
Country
Sweden
Region
Vastra Gotaland
Got an issue here that is harder than I expected to fix. The problem is that after a while, depending if the PCB is cool or not, all data bus'es gets high after a while. No picture is ever displayed.


Things to know:
- The PWR-led stays dimmed.
- This happened when the owner tried to upgrade from 3.0 to 3.1.
- I'm using the Dialoga 2.0 ROM's that I verified a few times during my tests that they work.
- The Caps button works a few pushes then stays off/on.


I have done the following:
- All clocks are checked and has the correct frequencies
- Checked all traces from U6A and U6B
- Checked for shorts
- Removed both U7 and U8 (CIA A-B)
- Removed the 68EC020 CPU and used a working Blizzard 1220


Any ideas? I cannot see any damage at the ROM sockets but will remove them tomorrow and see if there is something there. Maybe I will try to replace the MPU as well.


For a short period of time I was suspecting that it could not read from from the ROM's. The exact same behaviour occurs when I remove U6A or both of the ROM's and power on the Amiga.


Thanks in advance
 
Thread moved to AmiOracle as a more suitable place to get a response.
 
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