Just as the title says. I have two Apple ][ Plus boards (1 rev C, the other rev d) that are currently on the fritz . Both display garbage (or more accurately, the RAM state) on screen with no cursor and give no beep. However, I can state with certainty that it's not the CPUs or AutoStart ROMs, as all have been tested in another working board, and the CPU and AutoStart from the working board have been tested in the broken boards and the symptoms remain with the problem boards.
I have also tried using the ROM switch board from my Apple ][ with ][ Plus ROMs installed and get the same result.
Looking at the Sam's Apple II/IIe Troubleshooting and Rpair Guide isn't helping as the CPU and AutoStart are their only suggestions for the symptons decribed.
Any ideas?
Most probably one of these (in order of most likely first):
RAM (knock it down to just the first row of chips and get that working before populating the other rows).
POWER-UP RESET (check for a reset pulse on pin 40 of the CPU)
BUS DRIVERS (check the 8T28s or 8304 Data bus first; then the 8T97 address buffers).
OTHER DECODING LOGIC (ROM/RAM decoding logic)
So.… Out of curioucity, what are these "other logic ROM/RAM" ICs of which you speek?
I'm asking because I checked the reset and it's fine on both boards, I swapped the RAM with new-old-stock Ti 4116s and that did nothing, and I swapped the 8304s and 8T97s into a working ][+ and they turned out to be fine as well.
Well now you're going to get deep into the "glue logic" that makes it all work. Like the clocks, address decoders (74LS138), RAM multiplexors (74LS153, 74LS257), etc. Do you have a scope? Have you looked through Sather's "Understanding the Apple II" and/or Gayler's "The Apple II Circuit Description"?