First post, by whitepawn
- Rank
- Newbie
Recently i got myself an OAK OTI-077 ISA Graphics card from a local scrapyard about 2$. The card was mostly OK in physcial condition with one RAM chip missing and 3 Pins damaged in total. I have soldered back damaged pins and plugged it with one RAM chip missing just to see if any outputs that card have.
There was glitched output but obviously there is one RAM chip is missing so this is normal.
Checked my inventory for spare RAM chip (44C256) and i realized i don’t have any of it but i have plenty of HYB 514171BJ-50 with plastic sockets so i wonder if i can solve my memory issue with just one HYB 514171BJ-50 just like HMC HM86314Q graphics card.
Here is what i mean:
For fun and experiment i have started digging some specs and compare RAM types, pinouts and reverse engineered memory section of graphics card.(Reverse engineering of card is ongoing btw.)
Here is specs for original RAM chips:
- 2 pieces of M5M44256BJ 256K x 4-Bit DRAM (SOJ 20 Package) (FPM) (9 Address Bus+4 I/O Bus) 5V operation
6 pieces of M514256A 256K x 4-Bit DRAM (DIP Package) (FPM) (1 piece is missing) (9 Address Bus+4 I/O Bus) 5V operation
In total 1024kB of RAM
Here is specs for my intended RAM replacement:
- HYB 514171BJ 256K X 16-Bit DRAM (SOJ 40 Package) (9 Address Bus+16 I/O Bus) (FPM) 5V operation
1024kB of RAM
For easier reverse engineering of card I have removed DIP sockets from PCB and took high resolution pictures and created basic schematic of card with pictures and multimeter which you can find below:
I can share Kicad schematics if anyone interested but as i said schematic is an ongoing project.
Here my question begins for electronic gurus in forum. From datasheets and schematic i can understand that i have 16 i/o’s for new chip and i know where to solder them. For address lines main IC have 9 address pins for 4 RAM chips and 9 adress pins for another 4 RAM chips. Will it work with only one address bus (9 pins) connected to main IC? Or this approach is completely false? If it’s possible i want to know how. I have searched forum and internet for similiar approaches but couldn’t find any.
Any advices are welcome.