SNK Games (Neo Geo MVS / AES)

[channelmaniac]

Model: AES
Symptom: No sound

This was a bear to track down. Cleaned corrosion off the board. Cleaned the right end pins on each slot and socketed 3 chips to check the traces under them. Found a bad trace between E9 pin 6 (74LS11) and CN4 (front slot) pin 47A and Q3 pin 9 (74LS04). This trace was the Chip Enable pin on the sound program ROM. Patched the trace and tested the board.

[channelmaniac]

Model: Ikari III - The Rescue
Symptom: Garbled graphics a lines on the screen

Checked the board for damaged traces then started checking the video SRAM with the well calibrated finger. Found one (and received a blister on the finger) that was internally shorted. Found another one hotter than the others and checked it with a logic probe. It had bad looking signals on the data lines. Replaced both SRAM ICs and tested the game.

[channelmaniac]

Model: MV1
Symptom: Z80 Error

Swapped the Z80 chip with the proper Z80A. No change. Inspected the board closely and found some corrosion on 4 pins of a surface mount IC connected to the Z80 CPU. Continuity tests showed one trace was open. Cleaned the board and soldered in Kynar jumpers pm all 4 corroded traces to repair it.

Only one was needed to do the repair but by doing all 4 the board will last a lot longer for the customer.

[channelmaniac]

Model: MV2F
Symptom: Vertical lines in backgrounds

Pin 16 (D3 for Slot 2) on the NE0-257 IC at J2 was shorted to ground. Removed the IC and checked the trace on the board. The short was gone and was internal to the chip. Replaced the chip and tested the board.

[channelmaniac]

Model: MV4
Symptom: Slot 1 dead. Missing left channel on audio.

Checked the address lines and data lines on the Program ROMs for slot one. Found pin 15A on CTRG2 connector for slot 1 had a bad trace between it and C3 pin 7 (74LS245 IC). Patched the trace and tested the board.

Installed an audio cap kit to finish the repair.

[channelmaniac]

Tip: Cartridge ROMs

When troubleshooting cartridge issues it helps to know which ROM does what.

P ROM - 68K program (16-bit)
V1 ROM - ADPCM-A port (8-bit)   <-- Music & sound samples
V2 ROM - ADPCM-B port (8-bit)   <-- Music & sound samples

C ROM - VDP object tiles (32-bit)
S ROM - VDP overlay tiles (8-bit)
M ROM - Z80 program (8-bit)   <-- Sound Program ROM

[channelmaniac]

Model: MV4
Symptom: No audio from any slot or from self test

Installed an audio cap kit and the board would play the self test sounds but had no audio from carts. Replaced 1 74245 IC at location R1 on the lower board. The board would then play music and partial sound from carts. The Z80 CPU would lock up at set places on game cartridges when certain sounds were to be played.

Isolated the problem to the top board. Checked the ADPCM ROM address/data/control lines. They were perfect. Checked the sound program ROM. Pin 3 was stuck low. Replaced a shorted 74LS244 at location N5 on the top board to finish the repair.

[channelmaniac]

Model: MV4
Symptom: Z80 ERROR

Replaced the Z80 with the proper Z80A chip for the board. SNK was cheap and used slower rated parts at overclocked speeds.

[channelmaniac]

Model: MV4
Symptom Backup RAM Error

Backup RAM Error: Address D0814 Written 5555 Read 55D5. Replaced bad Backup RAM chip at D9. Board then came up with a Video RAM Error: Address 00803 Written AAAA Read ADAA. Replaced the Video SRAM IC at location L9.

Board came up but had very faint audio output. Installed an audio cap kit to finish the repair.

[channelmaniac]

Model: MV4
Symptom: "Z80 Error and sound failing"

Could not duplicate a Z80 error. The board immediately powered up with a Work RAM Error: Address: 00100008 Written AAAA Read AAA2.

Replaced a bad surface mount RAM at G9. Tested audio levels in the hardware test menu. Right channel was barely audible and left was not audible at all. Installed cap kit and tested.

[channelmaniac]

Model: MV1FS
Symptom: Stuck on Green - Calendar Error

Board had damage from a leaking battery. Customer removed battery before sending the board in.

Cleaned the board and jumpered a bad trace to fix the calendar problem. Board was stuck in a reboot cycle. Repaired another dead trace in the battery section that was sending power to a 74HC32 as part of the circuit for the enable lines on the Backup RAM. Replaced the missing battery and tested.

[channelmaniac]

Model: MV4
Symptom: Stuck on Crosshatch

User attempted repair damage. Tried a battery swap and board would no longer recognize any cartridge installed.

Found a knife scrape on the bottom board. Repaired 1 bad trace and jumpered another bad trace. Replaced 2 stripped screws.

[channelmaniac]

Model: MV2F
Symptom: Z80 Error

Replaced a bad Z80 chip with the proper (and faster rated) Z80A. Tested.

[channelmaniac]

Model: MV4FT2
Symptom: Audio would cut in & out.

The interconnect between the top and bottom boards that carries the signals to/from the Audio ROMs was broken on the bottom board side. Replaced the connector, installed a cap kit and a new battery, then tested the game.

[channelmaniac]

Model: MV4
Symptom: No audio. Would not keep settings in memory.

Battery read 7mv instead of 3.6v. Ran the game for an hour and the battery took no charge. Installed an audio cap kit and a new battery.

[channelmaniac]

Model: Street Smart
Symtpom: Dead

Replaced missing 6264 SRAM IC, fixed a short on the ROM board connector CN1 and resoldered it. Set the DIP switches and tested game.

[channelmaniac]

Model: Street Smart
Symtpom: Dead

Fixed bent pins on the audio output IC. The 12v line was shorted to ground and causing the switching power supply to go into shutdown.

[channelmaniac]

Model: Neo Geo AES
Symptom: Red screen with no cartridge installed

This symptom is indicative of bad Work RAM. Checked the board and found that several of the memory lines on both Work SRAM chips had been partially desoldered and that there was some chemical corrosion on the pads. There was also one existing repaired trace and several data line traces that had their coating scraped badly. Cleaned the pads up, resoldered the data lines, and checked continuity to the CPU. Patched one bad data line and coated the bare traces to protect them. Tested the game.

[channelmaniac]

Model: MV4
Symptom: Click of death

Battery leaked on the board and ate many traces. Cleaned both the top and bottom boards. Attempted repair on the bottom board but it was uneconomical to repair.

Swapped out the bottom board for one that was already repaired. Game then worked but Slot 4 had corrupt graphics. Repaired two traces on the top board to finish the repair.

[channelmaniac]

Model: MV4
Symptom: Low audio and garbled sounds

Installed an audio cap kit to restore sound and noticed that the sound effects and music were all mixed up. Generally this problem is caused by a bad IC at F1, F2, G1, or G2. Replaced those to no effect. Swapped out the SRAM and Z80 IC to no effect.

After the board sat overnight it would play the audio test tones in the hardware tests as garbled sounds when cold. This is a problem with the digital sound circuit and not a problem with the bottom board interfacing with the top board. Replaced a bad YM2610 IC and tested.

[channelmaniac]

Model: MV4
Symptom: Low audio and missing sounds

Installed an audio cap kit to restore sound and noticed that the sound effects for spelling the bonus word in Shock Troopers, 2nd Squad was missing. In Metal Slug the bonus sound from picking up fruit or other non-gun objects was missing.

Replaced a bad YM2610 IC and tested.

[channelmaniac]

Tip: Neo-Geo Cartridge ROM Functions:

P: Program ROMs

P1 is typically the main program ROM, it can be up to 8M and contains the entire game logic.

Some old PROG boards use 2/4M ROMs so P2-4 can be the rest of the P1 address space.

Then there's another address range used for a few different things such as the link circuitry, Fatal Fury 2 protection and later on it became used for another 8M+ of program ROM. ROMs mapped here are SP2 (P2 on the chip) if P1 is 8M.

EP1 replaces P1 with updated program code.

EP2 can be either the second half of EP1 if they're both 4M or can be the same thing as SP2 (8M+).

V are YM2610 ADPCM data ROMs.

There are actually two types of V ROM, one for the low frequency channel, one for the high. Games quickly started containing a chip called NEO-PCM which allows both channels to use the same ROM.

C ROMs only contain sprite data (which also makes up the backgrounds on the Neo), not the fixed tile layer data.

M ROM contains the Z80 sound engine program as well as the actual "track" sequences. Remember all sample data however is contained in the V ROMs.

S aka the "FIX" layer ROM contains the fixed (non-scrollable) tilemap layer that overlays sprites. Life/POW bars are made of this.

Thanks to Calpis on the Assemblergames.com forum for this info!

[channelmaniac]

Model: MV4
Symptom: RAM Error, written AAAA read A8AA

Board was shipped in a box that didn't allow for sufficient packing. 2 standoffs and the top cover were bent.

Replaced 1 bad SRAM IC at location H9, installed an audio cap kit, replaced 2 bent standoffs, and fixed the bent top cover. The audio is now loud and crisp.

[channelmaniac]

Model: MV4
Symptom: Stuck in watchdog. Customer requested a UniBIOS upgrade and a new battery be installed.

Repaired 3 broken traces. Tested board and found the audio level was low. Recapped the board to fix the audio problem. Replaced the battery and upgraded the system with a UniBIOS 3.0 chip.

[channelmaniac]

Model: MV4
Symptom: Backup RAM Error

Replaced bad surface mount SRAM IC and tested.