nztdm
Experienced Member
Hello!
I have acquired a Compaq Portable, and in the usual restoration process, backed up all the socketed ROMs.
Including the U35 RAM Decoder PROM (256 x 8; 82S123 type; mine is a TI TBP18S030N). According to the service manual, this can be changed to a version that will allow using 256Kx1 DRAMs in bank 2 and 3, instead of 64Kx1. This means 640K RAM on the system board instead of 256K, meaning a RAM card is no longer needed.
Another requirement is BIOS C or newer. Mine has BIOS C. I cannot find any of the later ones online.
The Compaq part numbers for these Bipolar PROMs are:
256K: 100349-001 (my one)
448K: 101256-001
640K: 101257-001 (the goal)
I have read the 256K one, and traced out where the pins go. I have tried to trace further but it is a neverending maze. This is probably not enough information; if you need more, please ask. I understand if this is too ambitious of a mission; just seeing if someone may have an idea. Everything in the pic below.
Cheers!
JD
I have acquired a Compaq Portable, and in the usual restoration process, backed up all the socketed ROMs.
Including the U35 RAM Decoder PROM (256 x 8; 82S123 type; mine is a TI TBP18S030N). According to the service manual, this can be changed to a version that will allow using 256Kx1 DRAMs in bank 2 and 3, instead of 64Kx1. This means 640K RAM on the system board instead of 256K, meaning a RAM card is no longer needed.
Another requirement is BIOS C or newer. Mine has BIOS C. I cannot find any of the later ones online.
The Compaq part numbers for these Bipolar PROMs are:
256K: 100349-001 (my one)
448K: 101256-001
640K: 101257-001 (the goal)
I have read the 256K one, and traced out where the pins go. I have tried to trace further but it is a neverending maze. This is probably not enough information; if you need more, please ask. I understand if this is too ambitious of a mission; just seeing if someone may have an idea. Everything in the pic below.
Cheers!
JD
Last edited: