I'm having a minor but irritating problem with my Rev 04 board. In diagnosing my Applesoft ROM problem on my RFI board, I had a situation crop up where there is no vertical hold.. the screen contents keep rolling upward. You can stop it with very precise adjustment of the vertical hold on the monitor, but of course this doesn't hold for long.
I googled like mad and of course vertical sync or hold brings up lots of monitor topics. I definitely do not have a monitor description. So then I pulled out the Apple 2 Circuit Description. It noted several IC positions relating to vertical sync. I swapped out each chip individually and then the whole set with working ones from my RFI. No change. I searched for bent pins, checked power supply voltages and tried another power supply. Made sure, via photos, that all the exact chips that had been working before were in their original homes (there had been some swapping when the RFI board was giving me grief). All as it was before.
What confused me and has me wondering if I understood the circuit description properly is a reference to a chip at A14. There is no chip there.. that is where the prototyping area is.
Got it. *B14* was the problem. I wonder if there was a typo of some kind in that guide. Soon as I swapped that 74LS02 out vertical hold was good.
I'm suddenly really glad I bought this 'DIY' motherboard with my II+ case. It has been a spectacular source of parts.
You'll become an "Apple Mechanic" yet.