NLG Users Repair Logs and Other Ramblings. Request your very own topic. Just ask any site staff. > Channelmaniac's Arcadecomponents' Old School Repair Logs

SNK Games (Neo Geo MVS/AES)

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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.

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