OK, some more progress on this board - some of which might even be positive!
I compared the d0 signal to that on another board, and found that this one is definitely not normal. So I decided to swap out IC33. Having done that, the signal at d0 now looks OK!![=D>]( "Applause")
But this actually made no difference to whether the machine boots up or not.
So, knowing that the connections from IC33 to VIDC are good (from previous tests), I had the idea of scoping out the activity on those lines. I found that d4 was actually stuck low, because the input pin on IC33 (pin 11) had one of those invisible fractures in the trace leading to the via. I fixed that using the normal "drill out the via and insert short length of wire" approach, and now d4 is properly connected.![:D]( "Very Happy")
Does the machine boot now? No it doesn't. In fact, it is now completely dead - there is no visible activity on any of the data lines that pass through IC33 (previously they were all active apart from d4).![:shock:]( "Shocked")
I must have done something stupid, but right now I can't figure out what!
I compared the d0 signal to that on another board, and found that this one is definitely not normal. So I decided to swap out IC33. Having done that, the signal at d0 now looks OK!
But this actually made no difference to whether the machine boots up or not. So, knowing that the connections from IC33 to VIDC are good (from previous tests), I had the idea of scoping out the activity on those lines. I found that d4 was actually stuck low, because the input pin on IC33 (pin 11) had one of those invisible fractures in the trace leading to the via. I fixed that using the normal "drill out the via and insert short length of wire" approach, and now d4 is properly connected.
Does the machine boot now? No it doesn't. In fact, it is now completely dead - there is no visible activity on any of the data lines that pass through IC33 (previously they were all active apart from d4).
I must have done something stupid, but right now I can't figure out what!Statistics: Posted by jms2 — Sat May 10, 2025 10:42 pm