MVS MV-2F Repair Logs

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Repairer: channelmaniac

Symptom: Audio would cut in & out

Cleaned corrosion off of 2 ICs, installed an audio cap kit, and reset the backup RAM.


Symptom: Graphics corruption and customer requested an audio cap kit to be installed. Screen looked like line 1 was missing every odd pixel and line 2 was missing every even pixel - repeat all the way down the screen. Some graphics elements were duplicated on the screen in the middle but were garbled and shrunken horizontally. Foreground and background graphics were affected but overlay text & health bars were not. The Neo Geo splash screen was affected but the "Winners don't do drugs" screen was normal.

Board had horrible patch work done to fix some cut traces that was covered with hot glue. I removed and redid the patchwork. They missed 2 traces that needed patching and a couple of the pins were shorting together. I cut the bad part of the traces out so the gouged ends wouldn’t touch each other then resoldered in new wire patches. Resoldered the NEO-B1 and the LSPCA2 ICs to fix the graphics corruption problem and installed the audio cap kit.

The 2 slot board didn’t have any support legs under the slot sockets. I suspect the flexing of the board by inserting and removing cartridges popped the legs loose from the solder pads on the board.


Symptom: Calendar error

Chip tested good by substitution. Replaced crystal but oscillator would not come up. Chip was in error condition with an output that slowly cycled high-low repeatedly. Checked all inputs/outputs on the chip and they all appeared normal. Checked power to the chip with a multimeter even though the power connections showed logic "high" - the chip power was not at the proper 5.0 volt levels. Jumpered a corroded platethru to fix the board.


Symptom: Missing audio from right channel after 5 minutes

This board was traded in as a "dead" board purchased off of eBay towards the repair of another board. Found 1 penny in the bottom of the box and found another two pennies and a dime wedged in the memory card slot. Removed the coins, straightened the pins and tested the board. Fixed the audio problem by recapping the audio section.

Replaced the memory card connector with one from a parts board to finish the repair. The original 2 slot arcade cabinet is set up to where the player can insert a memory card to save games. Apparently someone shoved coins in this slot.


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.


Symptom: Calendar Error message and Battery acid damage

Removed Battery and cleaned the acid damage. Repaired 1 broken trace to fix the calendar problem.

Board would boot and run but had no audio and lines on slot 2 that would come and go if the cartridge was wiggled. Cleaned slots and whole board thoroughly then installed an audio cap kit and a new battery.


Symptom: Locks up at boot

When running a cartridge with the "Winners Don't Do Drugs" screen, it would show the Neo Geo splash screen then the Winners screen before locking up.

Installed a UniBIOS chip and retrieved the crash info. The developer of the UniBIOS chip said the game was crashing within code.

Ran extended Work RAM tests (turn on all DIP switches) but found no errors. Ran CRC tests on the cartridges and found that none of the carts gave good CRC checks in this board.

Used a logic probe and verified that all of the program ROM data lines and address lines were active. Found that address line A18 was dead. The trace was good between slot 1 and slot 2 but not between the slots and the NEO-E0 chip, pin 40, and board location G3. Ran a jumper to fix the board.


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.


Symptom: Z80 Error

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


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.


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.


Symptom: Video RAM Error

Video RAM Error $8000 Written 5555 Read 0000

Replaced 2 bad CXK-5814 SRAM chips and tested.


Symptoms: Vertical lines on both slots

Board had a leaking battery. Cleaned up the battery corrosion and jumpered 2 traces between the NEO-257 and the NEO-ZMC2 ICs to fix slot 1. Jumpered a bad trace between slot 2 and the NEO-257 IC to fix slot 2. Installed a new battery and tested.


Symptom: Low audio on one channel and lines on screen

Battery was leaking. Removed battery, cleaned board, and installed cap kit to fix audio issue. Replaced bad NEO-257 IC to fix lines on screen. Installed new battery and tested.


Symptom: Video RAM Error

Video RAM ERROR $8000, Written 5555, Read FFFF

Replaced both CXK-5814 SRAM chips. Tested board. Replaced leaking backup battery and tested again.