SNK Games (Neo Geo MVS / AES)

[channelmaniac]

Model MV4FT2 (The 3rd, newest, and smallest verison of the 4 slot)
Symptom: Carts would not work in slots 1 and 2. No audio.

Strange thing was that you could put carts in 3 or 4... or 3 and 4 and it would work. Put a cart in slot 2 or slot 1 and you would get a crosshatch. Put a cart in 2, 3, and 4 then all three slots were usable. Put carts in all slots and the board would constantly reboot after doing self tests.

Repaired a bad trace between Slot 1 and 2, pin 13B on the program board connector and IC 1A, a NEO-244, pin 38. This was the program data line D8. Now all four slots would run cartridges.

The audio problem was tough to track down. The audio test worked so the bottom board was at least generating audio from the diagnostics.

Swapped the NEO-244 IC at A2. Nothing. Traced down all the connections between the slots and the NEO chips and then the NEO chips to the CN9 connector. Then traced it from the CN9 connector on the bottom board back through the 74xx logic to the 2610 Yamaha chip. Everything tested good.

Frustrated, I cleared the backup RAM and the sound magically returned. AAAAAAAAAAAAAHHHHHH!!!!!

[channelmaniac]

Model: MV1
Symptom: Backup RAM Error

Board was giving Backup RAM Error: Written 5555 Read 7255

Battery leaked on the board. Checked the traces to the Backup RAM. They tested good. Removed the battery, cleaned the corrosion, patched 2 bad traces from the NEO-F0 IC to the DIP switches, and replaced the Backup RAM at H6.

[channelmaniac]

Model: MV1
Troubleshooting RAM Problems

When troubleshooting RAM Problems on the MV1 the error message (Read 7255) can be broken down into upper bits (72) and lower bits (55)

The bits are kept in RAM as follows:

Backup RAM: Upper H6, Lower H5
Work RAM: Upper G3, Lower G4

The rest of the ICs will get filled in as I troubleshoot other boards.

[channelmaniac]

Model: MV1C
Symptom: No video sync

Board had no video sync. There is a 470 ohm SMT resistor tying the sync line high then a 100 ohm SMT resistor inline with a 74HC32 surface mount IC. The IC had inputs but the output was stuck high. Replaced the IC and the 100 ohm surface mount resistor.

[channelmaniac]

Model: MVS - MV2F
Symptom: Lines in player graphics and some background graphics for slot 2.

Logic probe showed pin 20 on the ZMC2 chip stuck high when a cart was being accessed in slot 2. Checked pin 9 on the NEO-257 at H/J2 and it was stuck high. Checked pin 16 and it had garbage for the inputs. Checked the trace from the NEO-257 to the slot and it was good. Replaced the NEO-257 IC to fix the board as its inputs were damaged.

[channelmaniac]

Model: Bootleg MV1C
Symptom: Plays for a couple of minutes then starts glitching

Board would get horizontal streaks on the display. Would get worse as game was played. Pushing on the SMT chips had no effect. Power cycled game and it worked again but played slower and the sounds were played slower as well then started streaking more and more until it lost sync and died. Resoldered the main video IC and system clock driver IC to no effect. No clock signal was coming from the 24MHz crystal. Checked the 1M and 100 ohm resistors and the 2 caps connected to the crystal. Checked soldering on the system clock driver IC. All checked good. Replaced the crystal and played a few games.

[channelmaniac]

Model: Bootleg MV1C
Symptom: Missing BIOS.

Burned a replacement BIOS ROM. Board booted and played but had no sound. Replaced missing sound pot and fixed a bad trace.

[channelmaniac]

Model: MV-1F
Symptom: Requires separate coin mechs for player 1 and player 2.

Unit had a 2 slot BIOS in it. (usa_2slt.bin) Replaced it with the standard USA BIOS (neo-geo.rom image) and played a couple of games to test.

[channelmaniac]

Model: MV4FS
Symptom: Dead. Had a note taped to it that there were lines in the graphics.

Unit was missing the BIOS chip. Programmed a replacement chip (27C1024) and booted it. It had lines in the graphics and was missing sounds. Board had been repaired before and had many chips replaced on upper and lower boards.  It also had a dark liquid spill on the top board.

Checked all the previous trace repairs. Reset the Backup RAM to fix the sound issue. Cleaned the top board and the slot connectors to fix the lines in the graphics. Reassembled the board and replaced all the missing standoffs, screws, and mounting feet.

[channelmaniac]

Model: MV4
Symptom: Dead. Click of death.

Bottom board had severe corrosion damage on the platethru holes and was beyond economical repair. Contacted customer and swapped out the bottom board with one that was already repaired. Slot 1, 2, and 3 had lines through the graphics and if a cart in slot 1 was bumped the board would reset. Cleaned the top boad and slots thoroughly to fix slots 2/3. Replaced the slot 1 connectors with ones pulled from a parts board to finish the repair. (No new ones are available.)

Customer reported the boardset was 300 feet from the ocean at an arcade which would explain the corrosion damage.

[channelmaniac]

Model: MVS MV-4
Symptom: Multiple - Backup RAM Error $D000, Calendar Error, audio, and slot problems

Purchased a 4 slot board to refurb and resell. It was sold as having a "RAM Error"

The board had a Backup RAM Error at $D000, Written 5555, Read 55F8. Since it was at the zero address boundary I checked the enable lines and the R/W line first. The R/W line was dead on the lower Backup RAM chip. Soldered in a 30ga kynar jumper between pin 8 of the 74HC32 IC at D8 and pin 27 of the Backup RAM at locaiton K8.

The board now booted but was stuck at the green screen - a calendar chip problem. The logic probe showed normal signals on all the pins of the 4990 IC but gave strange readings on the crystal. Checked the crystal with an oscilloscope. It was dead. Checked the traces around the crystal and found the trace from pin 13 on the 4990 IC was bad. Soldered in a kynar jumper and the board booted to the crosshatch.

Ran the board through tests and found the left audio channel was dead. Installed a cap kit to fix the audio problems.

Board would boot but not recognize cartridges. Isolated this to the top board. Checked the board thoroughly and found that the slots were dirty. Cleaned the board and slots then ran the board through a final set of tests in preparation for resale.

[channelmaniac]

Model: MV-4
Symptom: Crosshatch of death (wouldn't recognize cartridges)

Checked the traces under the battery and found the 3rd trace bad. Jumpered the first 4 traces as they were discolored and would eventually go bad. Installed a new battery and tested the system.

[channelmaniac]

Model: MV1
Symtpom: Audio cuts out

The audio would get very low and sputtery sounding at intermittent times. Board had a cap kit already installed. Narrowed it down to a dirty Stereo/Mono selector switch. Cleaned the Stereo/Mono selector switch and tested.

[channelmaniac]

Model: MV4
Symptom: Video RAM error

Board gave a Video RAM Error. Address 00000E17, Write 5555, Read 5557

Replaced the surface mount video RAM IC at K9. Reset the Clock/Calendar, replaced 2 missing screws, and tested.

[channelmaniac]

Model: MV4
Symptom: Z80 Error

Replaced the Z80 chip with a Z80A. Game would then boot but had no audio. Installed an audio cap kit to finish the repair.

[channelmaniac]

Model: AES
Tip: Diagnosing RAM problems

The AES is different than the MVS in that it does not display error messages on the screen if there are hardware problems. To diagnose problems, boot the system without a cartridge installed. The screen will turn different colors depending on the errors.

Blue = All tests passed
Red = WorkRAM error ($100000 region)
Green = PaletteRAM error ($400000 region)
Yellow = VideoRAM error
Pink = Bios selfcheck error ($C00000 region)
Cyan = Memory card error

The AES tests will only test the memory card if it is inserted and it is blank. It does NOT test the Z80 or other parts of the sound subsystem.

Many thanks to the folks at the neo-geo.com forums for this list!

[channelmaniac]

Model: MVS-2F
Symptom: Calendar Error message and Battery acid damage

Removed Battery and cleaned the acid damage. Repaired 1 broken trace to fix the calendar problem.

Board would boot and run but had no audio and lines on slot 2 that would come and go if the cartridge was wiggled. Cleaned slots and whole board thoroughly then installed an audio cap kit and a new battery.

[channelmaniac]

Model: MV1C
Symptom: Dead

MV1C arrived missing fuse. Replaced fuse and board was dead. Would come up with a white screen with 4 colored blocks. Cleaned board and inspected for damage. Resistor R79 (100 ohms) was broken off the bottom of the board. Replaced it with one from a parts board. Still dead.

Inspected the board further and found pin 40 (Vcc) was broken off of the BIOS ROM. Jumpered the pin to the body with a multimeter probe and the board booted to Work RAM test. Replaced the BIOS ROM with one from a parts board and set all jumpers to off. Board would boot but get stuck on a green screen.

Checked the clock/calendar crystal. It was dead. Replaced it and played a few games to test the board.

[channelmaniac]

Model: AES
Symptom: Needed custom BIOS installed

Customer wanted the system upgraded. It had the old Debug BIOS stacked on top of the AES BIOS chip.

Removed 1 resistor and the double stacked chips. Installed a new socket and a freshly programmed UniBIOS chip. Board would not boot. The UniBIOS file supplied by the customer was corrupt.

Programmed another EPROM with the UniBIOS 2.3 code and tested.

[channelmaniac]

Model: MV1C
Symptom: Backup RAM Errors

Backup RAM Error: Written: 5555 Read 5540

Found a broken trace between RAM 2 and RAM 4 on pin 20. Jumpered pin 20 from RAM 2 to pin 10 on U3 (74HC32.) Board then booted to:

Backup RAM Error: Written: 5555 Read 558E

Found an erratic signal on the R/W line (pin 27) of RAM 2. Jumpered pin 27 from RAM 2 to pin 6 on U3 (74HC32.) Cleaned the board and played a few games.

[channelmaniac]

Model: MV4FT2
Symptom: Click of Death

Board was stuck with a click of death problem. Swapped BIOS chips, still dead. Checked the address and data lines. All 16 data lines were stuck high. Used the "well calibrated finger" and found that the IC at location N3 (74AS245) connecting the CPU to the sound subsystem was shorted internally and getting very hot. Pulled the IC and tested it. It was bad, but replacing it did not free up the data lines.

Pulled the 2 74AS245 latches at C11 and D11 connecting the CPU data lines to the cartridge program ROM data lines. When tested they were found to be bad. Replaced them and system then booted up to a Video RAM error at 8000, written 5555 read 0000. Replaced both SRAM ICs to finish up the repair and tested the board.

[channelmaniac]

Model: MV2F
Symptom: Locks up at boot

When running a cartridge with the "Winners Don't Do Drugs" screen, it would show the Neo Geo splash screen then the Winners screen before locking up.

Installed a UniBIOS chip and retrieved the crash info. The developer of the UniBIOS chip said the game was crashing within code.

Ran extended Work RAM tests (turn on all DIP switches) but found no errors. Ran CRC tests on the cartridges and found that none of the carts gave good CRC checks in this board.

Used a logic probe and verified that all of the program ROM data lines and address lines were active. Found that address line A18 was dead. The trace was good between slot 1 and slot 2 but not between the slots and the NEO-E0 chip, pin 40, and board location G3. Ran a jumper to fix the board.

[channelmaniac]

Model: MV4
Symptom: Audio cuts in & out, memory backup not working

Board had been worked on before for an audio problem and had incorrect caps installed. Installed a cap kit and jumpered a damaged trace.

Replaced the backup battery then installed 2 missing hex standoffs and mounting feet. Replaced 2 broken mounting feet.

[channelmaniac]

Model: MV4
Symtpom: Audio cuts in & out

Installed an audio cap kit and tested the board.

[channelmaniac]

Model: MV4
Symptom: Dead - no click of death

Board fired up to a blank screen. No garbage on screen and no click of death. Power cycled the board a couple of times and it came up with a Work RAM error but no diagnostic info such as at what address or what was written/read.

Replaced the work SRAM IC at location D9 and tested board. No audio.

Installed an audio cap kit to finish the repair and tested the board.