MVS MV-1C Repair Logs

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Repairer: channelmaniac

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.

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.

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.

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.

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.

Symptom: Video RAM Error

Replaced 2 62256 surface mount SRAM chips and tested.