Hi, I just saw your post about your Apple II+ that won't boot.
Something that may be of some help is a gadget of mine called the ROMulator:
https://bitfixer.com/product/romulator/
This is a RAM/ROM replacement device that also includes the ability to halt a running 6502 and examine the contents of memory. I've used it to debug an Apple II+ myself (still in progress) and if the fault lies in bad RAM or ROM, this will find the issue pretty quickly since if you replace the bad section with the ROMulator's onboard memory, it should boot up.
Just thought this might be useful to you, please let me know if you have any questions. Thanks
- Mike