SNK Games (Neo Geo MVS / AES)

[channelmaniac]

Model: MV4
Symptom: Backup RAM Error (Written 5555, Read D555)

Replaced bad Backup RAM chip and tested board. Other Backup RAM chip was bad too. Replaced other Backup RAM chip and tested. No audio. Installed an audio cap kit and tested board. Replaced 3 missing screws holding the top cover on and inspected the top board for damage.

[channelmaniac]

Model: MV1
Symptom: Sound dies after board is powered on for about 30 seconds

Cleaned the Stereo/Mono audio selector switch and tested board. Customer requested an audio cap kit be installed.

Installed the audio cap kit and tested board. Battery had started leaking. Contacted customer and replaced it per his request. Reset the Backup RAM and set the system date/time. Played a couple of games to test.

[channelmaniac]

Model: MV1
Symptom: No Audio

The Stereo/Mono switch was physically broken off the board. Jumpered the switch to put the board into stereo mode then recapped the audio section. Replace the leaking memory backup battery. Reset the Backup RAM, set the date/time, and tested the board.

[channelmaniac]

Model: MV1
Symptom: Stuck on green

Checked pin 14 for +5v when board was powered up. It was there. Checked the 32.768KHz clock crystal and found it was dead. Replaced the crystal and played a game to test the board.

[channelmaniac]

Model: MV1FS
Symptom: Garbled audio

The audio wasn't muffled but rather was garbled in the digital section of the board. Soldered over several scratched traces to protect them and checked the DAC and looping Op-Amp IC connected to the DAC. Found the battery had leaked. Cleaned the board, resoldered 2 corroded plate thru to trace connections to fix the audio, and replaced the battery.

[channelmaniac]

Model: MV2F
Symptom: COLOR RAM ERROR Written 5555 Read 5755

Board came in with severe attempted repair damage. Removed both Color RAMs (4364/6264) and checked for damaged traces. Repaired 7 damaged traces and socketed the 2 Color RAMs. The Color RAMs tested good. Data 1 line on the Color RAM furthest away from the JAMMA connector had runaway pulses on pin 12.

Removed the 74LS273 at location A8 and this did not affect the error message. Replaced the NEO-G0 custom IC at location B9 to repair the board. Testing the board revealed that P1 Up did not work. Repaired a corroded trace at the JAMMA connector to finish the board repair and tested.

The memory backup battery had started leaking. Contacted the customer concerning the leaking battery and replaced it per his request.

[channelmaniac]

Model: MV2F
Tip: Troubleshooting Color RAM Errors

When troubleshooting Color RAM Error messages it's important to take the proper steps to quickly isolate the problems.

If the error message isn't at the beginning of the bank then one of the SRAM chips is bad. The first 2 characters of the READ string is handled by one chip and the last 2 characters by the other. In other words:

Written 5555 Read 5755 means the chip furthest from the JAMMA connector is bad.
Written 5555 Read 5557 means the one closest to the JAMMA connector is bad.

Replace the chip and test.

If the error is at the beginning edge of the bank, follow the steps above and replace the appropriate Color RAM chip. If that does NOT fix the problem then more in depth troubleshooting is needed.

First step is to check for damaged traces and repair them as necessary.

Next, carefully examine the output resistor ladders for damaged resistors. If these are found, the problem will most likely be a bad or damaged 74LS273 IC causing the Color RAM Error messages.

If the resistor ladder components are OK then check signals on the Color RAM with a logic probe. If signals are stuck low or high, check for shorts to ground. If the lines are not shorted then remove and test the Color RAM chips and 74LS273 ICs. If the lines are still stuck low then the problem will be with the NEO-G0 IC as it's the only component left to check.

If the signals are racing on the affected data pin when checked with the logic probe then do the same thing: Remove and test the Color RAM chips and the 74LS273 IC connected to the racing data line. If the line is still racing with those removed then replace the NEO-G0 chip.

Enjoy!

[channelmaniac]

Model: All
Tip: Checking the NiCd Battery for leakage

One funny thing about NiCd batteries are that they leak after they go bad. This isn't a normal kind of leakage you would expect from a battery but is rather a crystalline growth that appears on the terminals and spreads across the board and follows traces. This will eventually turn a telltale blue but when first starting out looks like simple dust.

Do not let this dust fool you!

When the battery starts to leak it must be replaced ASAP as the leakage will only get worse. This will eat traces and component leads. It will ruin sockets, chips, resistors, capacitors, and more. It doesn't care if the board is a common cheapie or a rare expensive one. It will leak just the same.

Here are 2 pics of the same battery. One is the shot of the positive terminal and the other of the negative. In one picture the solder joint is nice and shiny - a good looking solder joint. In the other you can see the growth on the battery and how it has already affected the solder joint. That isn't a cold solder joint but rather one that has been chemically corroded by the leakage from the battery.

When replacing these old NiCd batteries it is OK to use NiMH types with the same form factor. It is also OK to replace them with a battery having a higher milliamp hour rating such as replacing a 50maH with a 70maH rated battery.

Good luck, and replace those batteries before they ruin the game!

[channelmaniac]

Model: MV4
Symptom: Corrupt Graphics

Repaired 7 broken traces and tested. The board had poor audio and a leaking battery. Replaced the battery and recapped the board to finish the repair.

[channelmaniac]

Model: MV4
Symptom: RAM ERROR at location $8000

Replaced 2 bad CXK5814 SRAM Ics and tested board. Audio levels were low and the battery was leaking. Replaced the battery, recapped the audio section, and tested.

[channelmaniac]

Model: MV1C
Symptom: Video RAM Error

Replaced 2 62256 surface mount SRAM chips and tested.

[channelmaniac]

Model: MV6
Symptom: Missing Audio on slots 4 through 6

Jumpered a bad trace between pin 1 on IC B13 and pin of B17. Tested Game.

[channelmaniac]

Model: MV6
Symptom: Slots 4 and 5 dead

Slots 4 and 5 would show crosshatch when a known good cartridge was installed. Cleaned the slots aggressively with very fine emery cloth as the slots had bad corrosion problems due to liquid (possibly rodent) damage.

[channelmaniac]

Model: MV6
Symptom: Missing video on odd numbered slots

Games would play fine in the even numbered slots. The odd numbered slots had audio, but missing video - foreground, background, and text were all missing. Repaired bad trace between D3 pin 11 and C29 pin 15. Tested.

[channelmaniac]

Model: MV1FT
Symptom: Dead. Garbage on screen

Straightened a bent pin on the BIOS ROM, powered up the game, and received a SYSTEM ROM ERROR message. Programmed a new BIOS ROM, booted the system, and received a Z80 ERROR message. Replaced the Z80 CPU and tested. Splash screen sound was normal, but the games sounds were horribly mangled. Repaired a damaged trace to finish the repair and tested.

[channelmaniac]

Model: MV4
Symptom: Z80 ERROR

Address line A16 on the sound subsystem was racing. Replaced the most common problem chips first: CPU, SRAM, and the 74LS244, but the problem remained. Replaced the SM1 ROM IC to fix the error. Installed a cap kit to fix low audio issues and cleaned the slots to fix cartridge issues.

[channelmaniac]

Model: All MVS
Tip: BIOS Identification

Here's a tip from a former SNK employee:

Power up the MVS board without a cartridge installed. Look at the border color around the edge of the crosshatch screen. The color will reflect the region the BIOS is for.

Green: 6 slot, an older BIOS
Light Blue: USA BIOS, labeled SPU2
Dark Blue: Spanish BIOS, labeled SPS2
Red: Japanese BIOS, labeled SPJ2

[channelmaniac]

Model: MV2
Symptom: Calendar Error

Inspection of the board turned up gouged traces in several different spots. Removed 2 shorts and patched 9 broken traces. Tested game.

[channelmaniac]

Model: Aero Fighters 3 - MVS cartridge
Symptom: Dead

Board was a converted cartridge. When cart was placed in system, the system would exhibit the click of death symptoms. Installed a missing jumper for the CE* signal for the Program ROM and tested.

[channelmaniac]

Model: MV2F
Symptom: Video RAM Error

Video RAM Error $8000 Written 5555 Read 0000

Replaced 2 bad CXK-5814 SRAM chips and tested.

[channelmaniac]

Model: MV4
Symptom: Very low audio. Missing audio on slot 4

Recapped audio section to fix low audio issues. Replaced a bad 74LS244 on the top board to fix the missing audio on slot 4. Installed a new battery per owner's request.

[channelmaniac]

Model: MV6
Symptom: Slot 1 not working

Repaired 3 burned traces on the top board and tested. It appears the board was powered up wet since the traces that were burned were once that are grounded and next to the power pin on 3 of the 74LS244 ICs.

[channelmaniac]

Model: MV4FT2
Symptom: Graphic corruption, battery corrosion damage

Re-mounted the battery to the top side of the bottom board, jumpered 3 corroded traces on the bottom board, sealed up 8 scraped traces on the bottom of the bottom board, then cleaned the top board & slots. Removed a bent pin from slot 2, fixed the bad soldering on a user installed RCA jack connecting a pause button, and replaced 2 missing screws. Tested board.

[channelmaniac]

Model: MV4FT2
Tip: Battery corrosion damage

When the battery leaks on the MV4FT2 version of the Neo Geo 4 slot, there are 3 traces that run next to the battery area that control the graphics on the slots that can be affected by the corrosion damage. If this happens, the graphics will come and go, especially when touching pin 56 of the NEO-253 chip at D5 on the top board with a logic probe or oscilloscope probe.

The trace from this pin routes to the bottom board and is one of the three traces that run next to the battery area on the top side of the bottom board. These three traces will most likely be damaged and require jumpering with 30ga Kynar wire.

[channelmaniac]

Model: MV2
Symptom: Graphic corruption

Board had rodent damage on one of the NEO-257 ICs. Cleaned the board and slots then replaced a leaking battery. Tested.