Indeed, the tiny electrolytic in the VCO filter is known for leaking on some machines (I've seen it on RISC PCs and A7000s). It'd also explain the VIRQ error, because without it the VCO won't be stable. If there's no video output, removing it, cleaning that area of the board, and replacing the cap is a good idea if nothing else has worked.
You've already checked the address lines to VIDC, they go through RP16 and possibly RP15 -- but is the strobe from IOMD present?
(In case you're not familiar with the peculiarities of Archimedes/RISC PC video - the VIDC is a write-only device which uses part of the address bus and a strobe from the IOMD to write to the registers. Registers can't be read back because VIDC isn't connected to the data bus. If you don't have that strobe, it'll sit there twiddling its thumbs)
The VIRQ test programs VIDC to generate a standard video mode (something like TV-rate or 640x480) using the VCO. It times the VIRQ interrupt, which is triggered on a frame retrace (end of video frame aka Vsync interrupt).
SIRQ is similar but involves playing sound using one of the main clock reference sources: I think it's the 24MHz SYSCLK but it could be one of the other system clocks. It shouldn't be the CD Sample Rate clock because that's not present on Mk1 motherboards unless a 16bit sound upgrade is fitted.
You've already checked the address lines to VIDC, they go through RP16 and possibly RP15 -- but is the strobe from IOMD present?
(In case you're not familiar with the peculiarities of Archimedes/RISC PC video - the VIDC is a write-only device which uses part of the address bus and a strobe from the IOMD to write to the registers. Registers can't be read back because VIDC isn't connected to the data bus. If you don't have that strobe, it'll sit there twiddling its thumbs)
The VIRQ test programs VIDC to generate a standard video mode (something like TV-rate or 640x480) using the VCO. It times the VIRQ interrupt, which is triggered on a frame retrace (end of video frame aka Vsync interrupt).
SIRQ is similar but involves playing sound using one of the main clock reference sources: I think it's the 24MHz SYSCLK but it could be one of the other system clocks. It shouldn't be the CD Sample Rate clock because that's not present on Mk1 motherboards unless a 16bit sound upgrade is fitted.
Statistics: Posted by philpem — Fri Nov 08, 2024 9:02 am