Averias Frecuentes Neo Geo

10-sep-2007, 00:18

Neo Geo MVS System - diagnosing 4-slot SRAM locations

When reading error messages such as:

Written AAAA Read AABA

The AABA can be broken down into upper and lower bytes. AA is upper, AB is lower, and each byte is handled by a separate SRAM IC.

On the NEO-MVH MV4 (4 slot) board these are at the following locations:

Upper Backup RAM: D9
Lower Backup RAM: F9
Upper Video RAM: L9
Lower Video RAM: K9
Upper Work RAM: H9
Lower Work RAM: G9
Neo Geo MVS System - diagnosing 6-slot SRAM locations

When reading error messages such as:

Written AAAA Read AABA

The AABA can be broken down into upper and lower bytes. AA is upper, AB is lower, and each byte is handled by a separate SRAM IC.

On the NEO-MVH MV6 (6 slot) board these are at the following locations:

Upper Backup RAM: E9
Lower Backup RAM: F9
Upper Video RAM: L9
Lower Video RAM: K9
Upper Work RAM: J9
Lower Work RAM: H9
Neo Geo MVS system gives Backup RAM error
A four slot Neo Geo MVS gave a Backup RAM error: Address 00D00000; Written 5555; Read 0000. Battery corrosion on the board ate up a trace between the 10k resistor next to the battery and the 74HC32, pin 13 at location D10. This was causing a loss of a signal at pin 20 (/S) on the 256K SRAM chips. The loss of the signal meant the chips would not enter the write cycle.

Neo-Geo MVS system gives Bank 1 RAM error message
Replaced the CXK5864 SRAM ICs. If the message was Bank 0 then the LSPC IC needs replacing as that RAM is inside the IC.

Neo-Geo MVS system gives Main CPU RAM error message
Replaced the two 62256 SMT (Surface Mount Technology) SRAM ICs connected to the CPU. This error message could also be caused by bad traces on the board.

Neo-Geo MVS system gives Video RAM error message - address $0000
Replaced the 62256 SMT (Surface Mount Technology) SRAM ICs. Bad traces on the board can also cause this error.

Neo-Geo MVS system gives Video RAM Error at address $8000

Replaced CXK5814 SRAM ICs and tested board.

A second board with the same error had a corroded plated through hole on a trace between the SRAM and the LSPC IC. Jumpered the trace to fix the problem.

Neo-Geo MVS system gives work/backup RAM error message
Replaced 62256 SMT (Surface Mount Technology) SRAM ICs. These RAM chips are the ones with pin 24 connected to the backup battery for power. Defective traces on the board have also been found to cause this problem.

Neo-Geo MVS system gives a Z80 Error message

This one is tricky. Cleaned the cartridge edge and cartridge slot. This did not fix it. (Some carts have the sound ROM on the cart and a bad connection will give this error) Replaced the Z80 CPU to fix.

Error could be caused by the Z80, Sound ROM, 6116 SRAM IC, NEO-257 IC, NEO-G0 IC, or they YM2610 sound IC. Basically any problem that causes the sound system to appear unresponsive will give this error.

Neo-Geo MVS system has garbled video

Neo Geo 2 slot board worked and passed all RAM tests but video was messed up. The normal title screen was squished up into the upper half of the screen. The bottom half of the screen was a jumbled mess. During gameplay things on the screen changed on the upper half and bottom half at the same time.

Replaced one CXK5814 IC. IC tested fine on self tests and on an external tester. It had an internal addressing issue where the top addressing line had failed. When addressing the top half of the chip it would restart at the bottom of its memory. It would pass the simple memory tests of the Neo Geo and the external tester. Replacement of the chip cured the video problems.

Neo Geo MVS system is dead - has clicking from speakers
This system powered up but never appears to start its self tests. The clicking sound from the speakers meant that the watchdog circuit was resetting the CPU in an attempt to kickstart the system. Replaced the lower work SRAM IC to fix the board.

Neo Geo MVS system is dead - no clicking from speakers
This system powered up but never finished self tests. The missing clicking sound from the speakers meant that the watchdog circuit wasn't resetting the CPU. Found that the bottom board had bad battery corrosion damage. Removed the battery, cleaned up the damage, and checked the work and backup SRAM ICs with a logic probe. Found the /write signal missing on the lower backup SRAM. Patched the bad trace and replaced the battery.

Neo-Geo MVS system runs but will only display a white screen

Neo Geo 4 slot top board would only display a white screen with the "Insert Coin" and "Credit 0" text visible and that text was misspelled too. Sound and program ran normally.

Replaced 74LS244 ICs at locations N4, J4, E4, and A4 to fix. These are all tied together and a short in one will take out the other three.

Neo Geo MVS System shows crosshatch and won't recognize cartridges
Neo Geo MVS 4 slot gives a crosshatch pattern on the screen. Won't recognize any cartriges. The problem was 4 corroded traces going to connector CN10 from a nearby leaky backup battery. Ran jumper wires from CN10 pin B5 to B9 pin 18; CN10 pin B6 to B9 pin 3; CN10 pin A5 to B7 pin 2; and CN10 pin A6 to B7 pin 3 to fix.

10-sep-2007, 00:18	#1
GHISPANO Usuario registrado	Averias Frecuentes Neo Geo Neo Geo MVS System - diagnosing 4-slot SRAM locations When reading error messages such as: Written AAAA Read AABA The AABA can be broken down into upper and lower bytes. AA is upper, AB is lower, and each byte is handled by a separate SRAM IC. On the NEO-MVH MV4 (4 slot) board these are at the following locations: Upper Backup RAM: D9 Lower Backup RAM: F9 Upper Video RAM: L9 Lower Video RAM: K9 Upper Work RAM: H9 Lower Work RAM: G9 Neo Geo MVS System - diagnosing 6-slot SRAM locations When reading error messages such as: Written AAAA Read AABA The AABA can be broken down into upper and lower bytes. AA is upper, AB is lower, and each byte is handled by a separate SRAM IC. On the NEO-MVH MV6 (6 slot) board these are at the following locations: Upper Backup RAM: E9 Lower Backup RAM: F9 Upper Video RAM: L9 Lower Video RAM: K9 Upper Work RAM: J9 Lower Work RAM: H9 Neo Geo MVS system gives Backup RAM error A four slot Neo Geo MVS gave a Backup RAM error: Address 00D00000; Written 5555; Read 0000. Battery corrosion on the board ate up a trace between the 10k resistor next to the battery and the 74HC32, pin 13 at location D10. This was causing a loss of a signal at pin 20 (/S) on the 256K SRAM chips. The loss of the signal meant the chips would not enter the write cycle. Neo-Geo MVS system gives Bank 1 RAM error message Replaced the CXK5864 SRAM ICs. If the message was Bank 0 then the LSPC IC needs replacing as that RAM is inside the IC. Neo-Geo MVS system gives Main CPU RAM error message Replaced the two 62256 SMT (Surface Mount Technology) SRAM ICs connected to the CPU. This error message could also be caused by bad traces on the board. Neo-Geo MVS system gives Video RAM error message - address $0000 Replaced the 62256 SMT (Surface Mount Technology) SRAM ICs. Bad traces on the board can also cause this error. Neo-Geo MVS system gives Video RAM Error at address $8000 Replaced CXK5814 SRAM ICs and tested board. A second board with the same error had a corroded plated through hole on a trace between the SRAM and the LSPC IC. Jumpered the trace to fix the problem. Neo-Geo MVS system gives work/backup RAM error message Replaced 62256 SMT (Surface Mount Technology) SRAM ICs. These RAM chips are the ones with pin 24 connected to the backup battery for power. Defective traces on the board have also been found to cause this problem. Neo-Geo MVS system gives a Z80 Error message This one is tricky. Cleaned the cartridge edge and cartridge slot. This did not fix it. (Some carts have the sound ROM on the cart and a bad connection will give this error) Replaced the Z80 CPU to fix. Error could be caused by the Z80, Sound ROM, 6116 SRAM IC, NEO-257 IC, NEO-G0 IC, or they YM2610 sound IC. Basically any problem that causes the sound system to appear unresponsive will give this error. Neo-Geo MVS system has garbled video Neo Geo 2 slot board worked and passed all RAM tests but video was messed up. The normal title screen was squished up into the upper half of the screen. The bottom half of the screen was a jumbled mess. During gameplay things on the screen changed on the upper half and bottom half at the same time. Replaced one CXK5814 IC. IC tested fine on self tests and on an external tester. It had an internal addressing issue where the top addressing line had failed. When addressing the top half of the chip it would restart at the bottom of its memory. It would pass the simple memory tests of the Neo Geo and the external tester. Replacement of the chip cured the video problems. Neo Geo MVS system is dead - has clicking from speakers This system powered up but never appears to start its self tests. The clicking sound from the speakers meant that the watchdog circuit was resetting the CPU in an attempt to kickstart the system. Replaced the lower work SRAM IC to fix the board. Neo Geo MVS system is dead - no clicking from speakers This system powered up but never finished self tests. The missing clicking sound from the speakers meant that the watchdog circuit wasn't resetting the CPU. Found that the bottom board had bad battery corrosion damage. Removed the battery, cleaned up the damage, and checked the work and backup SRAM ICs with a logic probe. Found the /write signal missing on the lower backup SRAM. Patched the bad trace and replaced the battery. Neo-Geo MVS system runs but will only display a white screen Neo Geo 4 slot top board would only display a white screen with the "Insert Coin" and "Credit 0" text visible and that text was misspelled too. Sound and program ran normally. Replaced 74LS244 ICs at locations N4, J4, E4, and A4 to fix. These are all tied together and a short in one will take out the other three. Neo Geo MVS System shows crosshatch and won't recognize cartridges Neo Geo MVS 4 slot gives a crosshatch pattern on the screen. Won't recognize any cartriges. The problem was 4 corroded traces going to connector CN10 from a nearby leaky backup battery. Ran jumper wires from CN10 pin B5 to B9 pin 18; CN10 pin B6 to B9 pin 3; CN10 pin A5 to B7 pin 2; and CN10 pin A6 to B7 pin 3 to fix.