inaki wrote:I have taken a look at the thread where pokemon explains the shape I should get on A15.
I get a similar pattern to the one in the pictures for a couple of seconds. Then the signals starts changing. Some seconds later the signal is flat.
So it seems clear to me that some component is heating up and then fails.
Strange - but you could maybe test it when cooling some ICs down.
As cooling spray is quite expensive over the time you can buy a cooler for 40 pin ICs, put it in the freazer for a while to cool it to -18° and then put in on a either CPU or ULA to see if it's running longer. The signal on A15 shows video execution, if this is present it is working in general but due to heating some components its moving. But if the ULA is okay you should have at least a picture for a few seconds (K cursor). Print P after startup for PRINT (which is better to see) and put contrast to minimum and brightness to maximum.
In my opinion the missing black pixel is a ULA issue. I have one which has the same fault and shows only white level and sync level. As this is a 3-state signal (or 3 level signal) there is maybe one internal driver damaged which moves the signal from white level to black level (that is my guess, never opened the ULA).
But you should first fix the other issue with the A15 signal loose after a while without doing nothing.
Could be a RAM as well. If you want to increase internal RAM you should maybe do this first as SRAM parts are really cheap.