Sourcing parts for IOB6120 build, including obsolete and unobtainium components

DIGIKEY AND MOUSER COVERED MOST PARTS I NEEDED

The majority of all the parts are still stocked, either at Digikey where I bought most or at Mouser. That ran to about $120 between the two, including pricy parts such as the FPGA chip. Unfortunately a few were not even on the systems at either vendor or are marked obsolete and not stocked. 

MISSING ITEMS

I didn't have a source for the 4MB flash memory chip, the four SRAM chips, the CF socket and some 085C form factor 10uf polarized capacitors. I can work out a bodge for the capacitor, but the others were more critical to resolve. 

EBAY SOURCED SOME PARTS, THUS SOME RISK OF FAKES

I was able to find the SRAM chips listed on ebay from quite a few vendors. Those in China had a higher risk of being fakes as the industry that manufactures false chips is mainly centered there, but there were two vendors who at least claimed to ship from the US. No guarantee that the devices are any more correct but at least I can set up my Retro Chip Tester Pro to validate the parts before I solder them onto the board. 

The Molex CF socket is very obsolete and not stocked. I found one socket on ebay that superficially looks like the Molex part, but the vendor doesn't provide enough information to tell whether it matches the footprint and pin assignments of the Molex part. I took a gamble since it is not a very high priced item and purchased it.

INVESTIGATING SUBSTITUTION FLASH CHIP WITH EXISTING DESIGN

The part which seems to be pure unobtainium is the Sharp 4MB flash rom, LH28F400BVHE-BL85, that is in a 48 pin TSOP package. The usual suspect sites asking me to submit a request for quote popped up, but nothing looked too trustworthy in any case. I did search for similar chip types online and came up with a very limited supply of a different Sharp 32MB flash rom on Digikey. It was the same package type thus it was time to compare datasheets and pin assignments. 

At first glance, the pin assignments are almost identical and the differences are in most cases where the new chip has no connection to a pin that was wired on the old one. There are three additional address bits, of course, but those pins are not used on the old chip. 

The most serious red flag at first glance is that the missing chip has a BYTE control line that is N/C on the new chip. Thus, if the IOB6120 is trying to read/write in byte mode while the potential substitute is always a 16 bit word operation, we may have a problem. 

I will be scanning the data sheets rigorously, but I did buy the substitute right away since it is limited in quantities. I have to check the protocols, timing and other details carefully to be sure that I can substitute in this larger capacity chip successfully.