RAM chip

MVS RAM chips often fry due to overvoltage from a badly adjusted or failing cab power supply. It appears that the most common failure mode is the inability to write new data, resulting in errors during system self-test at the beginning of address ranges.

NeoGeo use multiples SRAM (Static RAM) types:

Work, Backup and lower Video RAM chips are 256k SRAM (5 volt, JEDEC pin compatible, 32K x 8bit) and only differ by speed. They have "256" or "257" in their markings
fast Video RAM (VRAM $8000~$87FF) chips are embedded into GRC or 16k SRAM (5 volt, 24pin DIP, 2K x 8bit, 35ns or faster)
Sound RAM chips are 16k SRAM (5 volt, 24pin DIP, 2K x 8bit, 150ns or faster) - fast Video RAM chip can be used as a replacement as they are faster (35ns).
Palette RAM chips are 64k SRAM (5 volt, JEDEC pin compatible, 8K x 8bit, 120ns or faster)

See memory speed for details about speed grades.

Pictures

Sony CXK58256 120ns
Work, Backup and Video RAM

Pinout and cross-refence

To do.

Replacement

For Work, Backup and Video RAM look for 256kbit SRAM, 5 volt, JEDEC pin compatible, 32K x 8bit, 120ns or faster in 28 pin SOIC package (not SOJ). Cypress, ISSI, UMC and Lyontek still make them and most today are 45ns, so any will do. This includes 62256, 43256, cxk58257, and others.

For fast Video RAM look for 16kbit SRAM, 5 volt, JEDEC pin compatible, 2K x 8bit, 35ns or faster in 24pin DIP package.
For Sound RAM look for 16kbit SRAM, 5 volt, JEDEC pin compatible, 2K x 8bit, 150ns or faster in 24pin DIP package. This includes the CXK5814, CYC128A, and 6116 ICs, provided they are fast enough.

For Palette RAM chips The can be replaced by 64k RAM chips off of old 386/486 motherboards (fast cache). CXK5864BSP-10L 28 pin dip LH5168N-80L 24 pin soic

Chips types and locations

MV-1

Work: CXK58256MM-12, G3 & H3
Backup: CXK58256MM-12, H5 & H6
Video: CXK58256MM-12, G4 & H4
fast Video: CXK5814P-35L, C5 & D5
Palette: CXK5864BSP-10L, H9 & H10
Sound: BR6116-100, H1

MV-1A

Work: KM62256CLG-7, RAM1 & RAM2
Backup: KM62256CLG-7, RAM3 & RAM4
Video: KM62256CLG-7, RAM5 & RAM6
fast Video: none
Palette: LH5168N-80L, RAM7 & RAM8
Sound: BR6216B-10LL, RAM9

MV-1B

Work: KM62256CLG-7, RAM1 & RAM2
Backup: KM62256CLG-7, RAM3 & RAM4
Video: KM62256CLG-7, RAM5 & RAM6
fast Video: none
Palette: none
Sound: BR6216B-10LL, RAM7

MV-1C

Work:
Backup:
Video:
fast Video:
Palette:
Sound:

MV1FS

Work: CXK58257AM-12LX, H4 & H5
Backup: CXK58257AM-12LX, H6 & H7
Video: CXK58257AM-12LX, B4 & B5
fast Video: CXK5814P-35L, C6 & D6
Palette: CXK5864BSP-10, H8 & H8
Sound: BR6116-10, K3

MV1FZ & MV1FZS

Work: KM62256CLG-7, RAM1 & RAM2
Backup: KM62256CLG-7, RAM3 & RAM4
Video: KM62256CLG-7, RAM5 & RAM6
fast Video: CXK5814P-35L, RAM7 &RAM8
Palette: XLJ6265AF-10SL, RAM9 & RAM10
Sound: BR6216B-10LL, RAM11

MV2FS

Work: LH52B256N-70LL, D3 & D4
Backup: LH52B256N-70LL, G1 & G2
Video: LH52B256N-70LL, C7 & C8
fast Video: CXK5814P-35L, C9 & D9
Palette: CXK5864BSP-10L, B8 & B8
Sound: BR6216B-10LL, K11

MV2-01

Work: LH52B256N-70LL, E5 & E6
Backup: LH52B256N-70LL, H3 & H4
Video: LH52B256N-70LL, F13 & G13
fast Video: CXK5814P-35L, F12 & G12
Palette: CXK5864BSP-10L, B9 & C9
Sound: BR6216B-10LL, K13

MV-4F

Work: CXK58256MM-12L, G9 & H9
Backup: CXK58256MM-12L, D9 & E9
Video: CXK58256MM-12L, K9 & L9
fast Video: CXK5814P-35L, L11 & M11
Palette: CXK5864BSP-10L, F4 & H4
Sound: BR6216B-10LL, L1

MV-6

Work: H9 & J9
Backup: E9 & F9
Video: L9 & K9
fast Video: CXK5814P-35L, M11 & N11
Palette: CXK5864BSP-10L, G4 & H4
Sound: BR6116-100, M1