Eureka! It is working! Changes I made are:
a. Pull the RR1 SIP and do not replace it.
b. Replace U18 and U19 with 74LS00. I did not try the 74ALS00's.
c. Lift Pins 2 and 5 of U18 and tie the lifted pins to Vcc with a small wire wrap wire jumper to pin 14.
d. Pull the four ICs (U10, U12, U13, U14) driving the hex displays and the LEDs. Remove the hex displays as they are no longer functional.
e. Replace Sandisk 256 MB card with Belkin 2 GB card.
Firmware is essentially per the MYIDE model but with some changes to the delay and timeout code and values.
I am using a 65 msec hard reset pulse with a 40 msec wait after the rest pulse is complete.
I had previously tried the Belkin card and it worked no better than the Sandisk 256 MB card. So why now?
Nothing but theory and that theory is that the smaller cards are older and do not support the faster PIO/True IDE modes of the larger and newer cards. Our 8-bit processors, especially the faster ones, probably stretch the older cards. I am sure there is a software solution but I am not likely to go down that path as the amount of time spent so far has been very heavy. Once I made the other hardware changes the Belkin was OK to go.
I may try adding the LED and hex display hardware back on the board but as noted previously they don't help since I can not really see them.
So right now I have two working 8 MB drives and may add a couple more. I may also add the ability to boot from the CF cards as I did reserve a track for each drive for system use and each track is 32768 bytes - more than enough to hold the system.
BTW - The 8255 is a Toshiba TMP82C55AP-10. All other ICs are 74LS.
If desired I will upload the BIOS and the MONITOR ROM code. The way I have my system set up you need both. For example the BIOS has the de-blocking code and then for both my floppy and the IDE/CF the BIOS calls the host & physical I/O code that is in the MONITOR ROM. It sounds complicated but is really simple. Console and printer I/O is via the S100 Computers Serial IO board. Floppy is an old heavily modified UFDC-1. Floppy drives are both 5.25 inch - one 1.2 MB the other a Kaypro IV compatible.
Rich Leary