DEC Professional 350 - video issue

Back in November I dropped in on a list member's moving giveaway and came away with some DEC stuff, among which was a DEC Professional 350 with keyboard and monitor. As the previous owner informed me, the video isn't working; there's no picture on the monitor, but there's visible sync lines, and the diagnostic lights on the back of the unit indicate an error with the bitmap graphics card. I'm pretty sure it's an issue with the card and not the slot, since the error moves with the card when I install it in one of the other slots, but I'm not sure what to look for on the card itself - nothing is socketed, so it's not chip creep, and the card connector looks to be in good shape. Does anybody have any advice for diagnosing and repairing this? I'd really like to get it working. Failing that, does anybody have a spare for the video card? (It's DEC part number 54-15138.) I've got a Rainbow I'd be willing to trade for a working one (base unit only - I don't have the facilities to test it, but according to the owner it was in working condition.)