Success! Well, sort of... I was swapping chips around between my two drive boards, and suddenly it worked! It turns out that UA1 in my primary board was bad, as swapping the chip in from my other board now allows the handshake to occur and the drive spins up when running a load command. Not sure why...

I should be getting more input probes later this week. As I said before, I'm looking for some guidance on which pins I should be looking at to compare signals on U2 and UC3. I have no idea how I would find this, so hopefully you have some information on that!

I only have 1 input probe for the oscilloscope right now, but I should have access to one within the next week, so once I get that I can give that a try. However, I 'm not sure how to find the corresponding pins on UC3, and I was able to figure out a few using the information you sent with the scope...

Actually, it freezes when the drive is ON and plugged in; if the drive is off or unplugged from IEC, I do get a NOT PRESENT and READY message. I do have both C64’s and both have the same results all around, which is why I suspect the drive. Unfortunately, I can’t test because I have had no power in ...

The only pin I actually caught a signal on when running the program with 1541 on was pin 5. Interestingly, the signal seems the same as your image up to a certain point, where it just continues straight. It seems to me that this could indicate it behaving normally and then crashing when it stops fol...

I have 2 drives, with one working mechanically (the other not) and the state of the 2 logic boards is not promising. One of the boards looks like it has had a good bit of repair work done (poorly), so I’m a bit less hopeful with that one, though they both yield the same result: a crash whenever tryi...

Unplugging the 1541 raised pin 9 up to 4.39V, so I'm good with that. So given this, I think I can be mostly confident that U2 is properly trying to make contact with the drive. Now I will try to see what the signals on both devices look like with the 1541 on, but as you suggested earlier, this may b...

Well, it's been a while, but I finally got around to looking at the signals on pins 7 and 9 of the CIA. With 1541 off, I'm seeing nothing on pin 7 (which makes sense) but 2.7V on pin 9, which is lower than the 5V at which it should be. I'm still not 100% sure that I am using the oscilloscope right f...

Yeah, that time scale was too far zoomed in. Looking much better now; pins 5, 6 and 8 all look almost exactly like yours. That's a good sign! Pictures below. The ground lead is attached to the heatsink for VR2 on the C64, which should be fine. I didn't realize how to reset the trigger, so that was m...

I apologize for my lack of oscilloscope background. I’m learning as I go!