The board arrived with me. POSTbox output showed occasional SIRQ fails (with timer value, so some SIRQ was just slow sometimes) as well as the VIRQ fail (always FFFF, so 2nd never happend). Board in worse condition than I expected, so did some initial cleanups, including adding back the missing CMOS RAM chip so that testing was easier. Pins for the battery. Plenty of rot in this area, but at least it all now works...Checking around VIDC with the scope, curious that we see no FLBK but we do see VSync. VIDW also operating as expected. Start buzzing all the connections and right near the end ... D27 is open circuit! D27 is obviously connected from ARM to ROMs, or we wouldn't get a running RISC OS, and the ROMs are close to VIDC, so that's a surprisingly small area for the fault to lie. Further buzzing on D27 showed VIDC is connected to IC17 (IOC databus latch) but from there not to the ROM chip that's directly next to it. The trace runs horizontally on the underside of the board and what do we find...
Some nasty green sticky goop right on the trace that's failed. Strip and clean. Yep, broken. Patch it up. Sorted - clean POST and straight to desktop. All good.
What nastyness caused this rot all the way over here, who knows?
More testing of all the other board functions ongoing (I'm surprised the IDE works - lots of tracks are in a bad way). But at least that's the fault as reported now solved.![\:D/]( "Dancing")
More testing of all the other board functions ongoing (I'm surprised the IDE works - lots of tracks are in a bad way). But at least that's the fault as reported now solved.
Statistics: Posted by IanJeffray — Sat Jan 20, 2024 11:11 pm