MVS MV-4FT2 Repair Logs

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Repairer: channelmaniac

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!!!!!

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.

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.

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.

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.