IBM Fixed Disk Adapter - BIOS ROM
As written at here, the BIOS ROM is a Mostek MK36000 or equivalent.
If that ROM fails, needing replacement, the replacement situation is the same as for the ROM's used on the IBM 5150 (IBM PC) motherboard. And so see the 'Use of an EPROM/EEPROM to substitute' section of here for what options are availble to you.
Code to go into the replacement EPROM/EEPROM can be found at here (where the make is shown as 'IBM (Xebec)').
For example, the photo at here shows me successfully using a TMS2564 EPROM (2564, not 2764) as the replacement.
For example, the photo at here shows me successfully using a 27C256 EPROM as the replacement. Undesireable because the IBM Fixed Disk Adapter will then take up two slots in the computer. See here for a method of quadrupling the 8 KB sized image available online, to get a 32 KB sized image to go into the 27C256.