Hi,
as I can literally see the tumbleweed blowing across this thread, I thought may as well post the first reply.
Just a quick update on my problem: I have now managed to boot the SE30 (see pic) off the floppydrive (good!) but I had to disconnect the harddrive (bad). Could the SCSI chip be gone? Sound is OK.
Looking at the bars and their pretty regular appearance I have tried to come up with a possible cause for this. I'm probably way off but how about the output (pin7) of the first mux in UD8 (the 74253) being stuck at 1 (aauming the VRAMS chips are ok)? This seems to supply the least significant bit to the address decoder of the VRAM, which could (???) create the 8 pixel wide bars on the screen. Am I right in assuming that the VRAM is interleaved between the two chips (lower 4 bits from UC7 and upper 4 bits from UC6) which are then going to the serial shift register (UE8)?
I would really be interested in what the experts think about this.
Cheers!
PS: Does anyone know how the VRAM is tested on boot-up? Could it be a checkerboard test which may explain the shape of the bars (10101010 on first line versus 01010101 on the next line)?
as I can literally see the tumbleweed blowing across this thread, I thought may as well post the first reply.
Just a quick update on my problem: I have now managed to boot the SE30 (see pic) off the floppydrive (good!) but I had to disconnect the harddrive (bad). Could the SCSI chip be gone? Sound is OK.
Looking at the bars and their pretty regular appearance I have tried to come up with a possible cause for this. I'm probably way off but how about the output (pin7) of the first mux in UD8 (the 74253) being stuck at 1 (aauming the VRAMS chips are ok)? This seems to supply the least significant bit to the address decoder of the VRAM, which could (???) create the 8 pixel wide bars on the screen. Am I right in assuming that the VRAM is interleaved between the two chips (lower 4 bits from UC7 and upper 4 bits from UC6) which are then going to the serial shift register (UE8)?
I would really be interested in what the experts think about this.
Cheers!
PS: Does anyone know how the VRAM is tested on boot-up? Could it be a checkerboard test which may explain the shape of the bars (10101010 on first line versus 01010101 on the next line)?