VIC-II:
pin 8 is 0.1v, should be 4.9 P according to the SAMS schematic (IRQ)
pin 9 is 0.42, should be 4.9 P (ROW4, whatever that means)
CPU: pin 3 is 0.1, should be 4.9 P (IRQ)
CIA u1: pin 21 is 0.1, should be 4.9 P (IRQ)
(these connect to each other, continuity is ok)
User port B is 5.09v, should be P
Keyb pins 13-19 are ~5.07v, should be P
There are many other variations but basically anything that should be L is ~0, H is ~4-5, and P is somewhere in betweenish.
Personally I can't tell much of anything from that.
There are some fun ("fun") tests later in the book to check readings while pressing certain keys and so on. I'll do that while I'm waiting for the dead test to arrive.
The c64 was in more or less regular (monthlyish) use ~10 years ago (as the office MULE competition machine ). I pulled it out of storage about 3 years ago which is when it worked briefly before dying. I did some checks at the time, just pulling out various chips to see the reaction as per some very basic troubleshooting guide, and you know, now that I think of it, I might've done the stupid mistake of accidentally swapping the pla and sid at the time. That could explain why they were both dead. So, perhaps my original issue was the garbled screen, and I just broke it further. Can't be sure but it kind of makes sense and rings some tiny bells in my brain. But, anyway, PLA is fixed and SID is removed, so I guess I'm back at my garbled screen. No one else has tried anything on the c64 and it looks quite pristine overall, no signs of post-factory soldering or tinkering as far as I can tell.Gyro Gearloose wrote: ↑Sat Jan 23, 2021 8:44 pm Well I guess I can ask more questions: did this 64 ever work correctly? Has anyone else tried to repair it? What is the part number of the VIC-II and what is the frequency written on the crystal?