For what it's worth I recapped an SE/30 recently with a horizontal line on screen-- no change after recap. The culprit turned out to be a via near UF8.
From the schematic, UF8 appears to count vertical lines. The output goes to PAL UG6 which probably implements comparators at 342 and 370 lines to generate the VSYNC pulse. Bad connection from UF8 = no match on the comparator = no VSYNC pulse, I think.
Half-baked idea based on the above: UG7 looks to do something similar for HSYNC. Change the comparators on these two (by lifting VSYNC and HSYNC off the PALs or swapping data lines around) to get larger horizontal and vertical resolution. Then overclock to get back to 22.25kHz horizontal scan rate, though either lower vertical refresh or non-square pixels.
Probably the video memory would be the downfall of that plan though-- not sure it would be big enough. And beyond that, there would be ROM changes to teach the new resolution....
From the schematic, UF8 appears to count vertical lines. The output goes to PAL UG6 which probably implements comparators at 342 and 370 lines to generate the VSYNC pulse. Bad connection from UF8 = no match on the comparator = no VSYNC pulse, I think.
Half-baked idea based on the above: UG7 looks to do something similar for HSYNC. Change the comparators on these two (by lifting VSYNC and HSYNC off the PALs or swapping data lines around) to get larger horizontal and vertical resolution. Then overclock to get back to 22.25kHz horizontal scan rate, though either lower vertical refresh or non-square pixels.
Probably the video memory would be the downfall of that plan though-- not sure it would be big enough. And beyond that, there would be ROM changes to teach the new resolution....