Black screen on C64; continuous IRQ from VIC?

Hi all, I bought a C64 marked "non-working" at last year's VCF East as a project machine. Alas, I wasn't able to make it to Bil Herd and Rob Clarke's session on Commodore maintenance at the same show, so perhaps I missed this part. :-) Anyway, the screen is totally black, but it is syncing. I've verified on my scope that the VIC is generating the proper NTSC vertical and horizontal syncs, as well as the color burst, but there's no content. On further inspection, I've found that the IRQ line is pulled low as soon as the reset line is released, and it does not release. If I pull the VIC chip, the IRQ does not do the same thing. I know better than to assume correlation is the same as causation; it's entirely possible that by pulling the VIC, I've caused some crash in the initialization sequence that would cause one of the CIAs to pull the IRQ line constantly or something of the sort. I'm a Commodore newbie, so I don't know how the thing is *supposed* to behave, but I do know that a constant low on the IRQ line is going to keep the CPU from doing anything terribly useful unless it's masked. Anyone have advice? Is my VIC blown? I sure hope not, because those things are not easy to find outside of finding a scrapped C64. - Dave