MVS MV-4 Repair Logs

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Repairer: channelmaniac

Symptom: Missing background graphics

There's a 74LS138 on the top board. It's a 3 to 8 decoder. It's used to enable the slot wanted. Not part of the repair, but just wanted to doc it on the forum. Also, there are a LOT of 74LS244 buffers & 74LS245 latches on the board. Each one is hooked together with the neighboring chip that is doing the same function on each of the different slots. In other words, each cartridge slot has multiple buffers and latches. Each latch for specific connections (program data lines 0-8, for example) on the cartridge slot has their board side connections (not cartridge side connections) tied together to the connectors that take the signal to the bottom board.

Now, on to the repair:

Test Cart used: Shock Troopers, 2nd Squad.

This top board had a totally white screen with the exception of the "insert coin" words in the center and the "credit 0" at the bottom right and even that text was mispelled...

Used a logic probe to check each and every chip for input and output logic levels. Found a 74LS244 next to slot 4 that had incorrect levels for input vs. output. In tracing the pins on the chips I discovered that there is a chip doing the same thing for each of the slots and they are all tied together. That makes 4 video ROM buffers - one for each slot - all tied together when the connect to the bottom board.

Why does it matter that they are tied together? Well, when one shorts it tends to draw excessive current through the others and takes them out too.

Replaced the 74LS244 chips at locations N4, J4, E4, and A4 to fix.


Symptom: Cartridges do not work. Crosshatch pattern is all you get on the screen, no matter what slot. Unusual in that the problem follows the top board when swapping boards out.

Resolution: There is a 74F138, 3 to 8 decoder, at position A2 that determines which slot is active. Fixed broken trace on one of the 3 enable lines to allow the system to switch the slots and access the cartridges.


Symptom: Vertical lines in the graphics on slot 3.

Resolution: The graphics ROMs connect to the system board through a series of 74F253 ICs. These are dual 1 of 4 line selectors. Pin 21B on the bottom cartridge slot connector's data wasn't seen on the output (pin 9) of the 74F253 at position D1. Patched the trace to fix.


Symptom: Crosshatch of death

Crosshatch of death is where the board shows the self test crosshatch screen. It is not recognizing any cartridges inserted into the board.

This is a common problem on the older, larger 4 slot board. The NiCD backup battery will leak and eat through traces that run under and next to it. Trace the lines with a multimeter from the connector next to the battery and run jumpers to patch any bad traces.

That connector is what the system uses to access the program ROMs on the cartridges. If it can't read and run the program then it cannot detect and use the cartridges.


Symptom: Garbage on screen / Click of Death (Stuck in Watchdog)

This one had some physical damage that someone did a half-ass repair on. It's ugly as sin but the trace they patched is working.

The board would display nothing but garbage and would constantly do a click click click - watchdog circuit was trying to restart the system.

Replaced 2 74LS245 ICs at locations B7 and B8. Both were shorted and getting very hot.

Board was still in watchdog restart.

Patched a bad trace on data line D16 between the upper Backup RAM and the upper Data RAM. Now the board would constantly go through self test and restart with garbage on the screen. It was a different restart than with the watchdog circuit.

Examined the board under a magnifying glass and found one more gouged trace the previous tech missed between data line D1 on the CPU and pin 60 on the PRO-C0 chip. Patched the trace and the board is now running fine.


Symptom: Corrupted Graphics

The Neo Geo logo screen had the words broken into jumbled blocks and there were "0" (zeros) down the left and right sides of the screen.

Checked the board for broken traces. Did not find any. Swapped the top board with my test board. Same problem - it's on the bottom board. Replaced the 2 74LS244 buffer chips that were driving the address lines for the graphics ROMs. No change.

This was still an address line problem since the problems were in blocks and not in vertical lines on the screen.

Took the logic probe and checked each address line at the top board. Noticed one of the lines only had a slow pulse on it instead of activity. Shorted it to the next address line over and the zeros went away and there was just garbled graphics. Traced that line back and found where there was a very small area of board between connector CN8 and the edge of the board that had taken a hit.

Patched the broken trace to fix the board.


Model: MVS MV-4 Dignosing bad RAM ICs

Board is a NEO-MVH MV4 (4 slot)

Backup RAM Error:

Address    Write  Read
00D01406   AAAA   AA2A

The Read code is broken up into 2 parts... AA and 2A

The first 2 characters are the upper bits and are handled by the IC at D9 The second 2 characters are the lower bits and are handled by the IC at F9

---

Video RAM Error:

Address    Write  Read
00000607   5555   5455

Same thing here... the Read code is broken up into 2 parts... 54 and 55

The first 2 characters are handled by the IC at L9 The second 2 characters are handled by the IC at K9

---

Work RAM is laid out backwards from Backup RAM and Video RAM on the NEO-MVH MV4

Work RAM Error:

Address    Write  Read
xxxxxxxx   AAAA   AABA

(Yeah, I was too lazy to write down the exact address of the error...)

The first 2 characters are the upper bits and are handled by the IC at H9 The second 2 characters are the lower bits and are handled by the IC at G9


Symptom: Audio would cut in & out

Installed an audio cap kit, and reset the backup RAM.


Symptom: Lines in background graphics and audio would cut in & out

Swapped top board out and narrowed problem down to the bottom board. Found a gouged trace between pin 27A on connector CN9 and pin 8 of IC PRO-CT0. Patched trace to fix the graphics problem. Installed an audio cap kit and reset the backup RAM to finish the repair.


Symptom: Click of Death

Board was stuck in watchdog reset and had battery corrosion damage. Board already had wire jumpers already on it to fix a crosshatch of death problem.

Cleaned the corrosion as best possible. Checked the control lines on the Backup RAM and Work RAM. They were stuck high meaning the chips weren't being accessed. Checked the enable line (pin 20) on the BIOS and it was stuck high. There was a problem in the decode or read/write circuitry. Checked around the chips near the battery for traces eaten by corrosion. Found pin 9 on the 74LS05 at location D11 had a bad trace connecting to pin 5 of the 74LS259 at location C5. Ran a jumper to fix the board.


Symptom: lines in graphics and sound problems on top board

Swapped top boards out to narrow problem to the top board. Lines in the graphics were NOT the same for all 4 slots. Slot 4 was perfect. Slot 3 had 2 repeating vertical lines. Slot 2 had a single repeating vertical line. Slot 1 had every other vertical line missing. All slots had the same sound problems: missing tunes, incorrect tunes, and garbled sound effects.

Found 3 bad traces in the sound circuitry between the board connector CN11 and the buffer/latch chips. Fixed at trace between pin 4 of R6, L6, G6, and C6 and pin 5A of CN11. Fixed a trace between 6B of CN11 and pin 3 of S6, M6, H6, and D6. Fixed a trace between 12B of CN11 and pin 9 of S6, M6, H6, and D6. Tested all 4 slots and sound was working fine.

Checked slot 3 and found 2 bad traces in the area between the slot and the 4 to 1 data selector IC (74F253) at A7 and at B7. Ran a jumper from pin 4 of A7 to cartridge connector CTRG5, pin 33A and a jumper from pin 4 of B7 to CTRG5, pin 34A to fix the graphics problem on slot 3.

Checked slot 2 and found a nasty looking signal on pin 11 of the 4 to 1 data selector IC at C1 (74F253). Checked continuity to pin 20B of CTRG3 and found it good. Looked closely at the pin on the cartridge slot and found slight corrosion. Cleaned the pin and the slot tested good.

Slot 1 had a bad trace between pin 46 of CTRG1 and pin 10 of P7 (74F253). Jumpered the trace and tested the slot.


Symptom: Dead. Click of death.

Bottom board had severe corrosion damage on the platethru holes and was beyond economical repair. Contacted customer and swapped out the bottom board with one that was already repaired. Slot 1, 2, and 3 had lines through the graphics and if a cart in slot 1 was bumped the board would reset. Cleaned the top boad and slots thoroughly to fix slots 2/3. Replaced the slot 1 connectors with ones pulled from a parts board to finish the repair. (No new ones are available.)

Customer reported the boardset was 300 feet from the ocean at an arcade which would explain the corrosion damage.


Symptom: Multiple - Backup RAM Error $D000, Calendar Error, audio, and slot problems

Purchased a 4 slot board to refurb and resell. It was sold as having a "RAM Error"

The board had a Backup RAM Error at $D000, Written 5555, Read 55F8. Since it was at the zero address boundary I checked the enable lines and the R/W line first. The R/W line was dead on the lower Backup RAM chip. Soldered in a 30ga kynar jumper between pin 8 of the 74HC32 IC at D8 and pin 27 of the Backup RAM at locaiton K8.

The board now booted but was stuck at the green screen - a calendar chip problem. The logic probe showed normal signals on all the pins of the 4990 IC but gave strange readings on the crystal. Checked the crystal with an oscilloscope. It was dead. Checked the traces around the crystal and found the trace from pin 13 on the 4990 IC was bad. Soldered in a kynar jumper and the board booted to the crosshatch.

Ran the board through tests and found the left audio channel was dead. Installed a cap kit to fix the audio problems.

Board would boot but not recognize cartridges. Isolated this to the top board. Checked the board thoroughly and found that the slots were dirty. Cleaned the board and slots then ran the board through a final set of tests in preparation for resale.


Symptom: Crosshatch of death (wouldn't recognize cartridges)

Checked the traces under the battery and found the 3rd trace bad. Jumpered the first 4 traces as they were discolored and would eventually go bad. Installed a new battery and tested the system.


Symptom: Video RAM error

Board gave a Video RAM Error. Address 00000E17, Write 5555, Read 5557

Replaced the surface mount video RAM IC at K9. Reset the Clock/Calendar, replaced 2 missing screws, and tested.


Symptom: Z80 Error

Replaced the Z80 chip with a Z80A. Game would then boot but had no audio. Installed an audio cap kit to finish the repair.


Symptom: Audio cuts in & out, memory backup not working

Board had been worked on before for an audio problem and had incorrect caps installed. Installed a cap kit and jumpered a damaged trace.

Replaced the backup battery then installed 2 missing hex standoffs and mounting feet. Replaced 2 broken mounting feet.


Symtpom: Audio cuts in & out

Installed an audio cap kit and tested the board.


Symptom: Dead - no click of death

Board fired up to a blank screen. No garbage on screen and no click of death. Power cycled the board a couple of times and it came up with a Work RAM error but no diagnostic info such as at what address or what was written/read.

Replaced the work SRAM IC at location D9 and tested board. No audio.

Installed an audio cap kit to finish the repair and tested the board.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


Symptom: Backup RAM Error

Replaced bad surface mount SRAM IC and tested.


Symptom: Backup RAM Error (Written 5555, Read D555)

Replaced bad Backup RAM chip and tested board. Other Backup RAM chip was bad too. Replaced other Backup RAM chip and tested. No audio. Installed an audio cap kit and tested board. Replaced 3 missing screws holding the top cover on and inspected the top board for damage.


Symptom: Sound dies after board is powered on for about 30 seconds

Cleaned the Stereo/Mono audio selector switch and tested board. Customer requested an audio cap kit be installed.

Installed the audio cap kit and tested board. Battery had started leaking. Contacted customer and replaced it per his request. Reset the Backup RAM and set the system date/time. Played a couple of games to test.


Symptom: No Audio

The Stereo/Mono switch was physically broken off the board. Jumpered the switch to put the board into stereo mode then recapped the audio section. Replace the leaking memory backup battery. Reset the Backup RAM, set the date/time, and tested the board.


Symptom: Stuck on green

Checked pin 14 for +5v when board was powered up. It was there. Checked the 32.768KHz clock crystal and found it was dead. Replaced the crystal and played a game to test the board.


Symptom: Corrupt Graphics

Repaired 7 broken traces and tested. The board had poor audio and a leaking battery. Replaced the battery and recapped the board to finish the repair.


Symptom: RAM ERROR at location $8000

Replaced 2 bad CXK5814 SRAM Ics and tested board. Audio levels were low and the battery was leaking. Replaced the battery, recapped the audio section, and tested.


Symptom: Z80 ERROR

Address line A16 on the sound subsystem was racing. Replaced the most common problem chips first: CPU, SRAM, and the 74LS244, but the problem remained. Replaced the SM1 ROM IC to fix the error. Installed a cap kit to fix low audio issues and cleaned the slots to fix cartridge issues.


Symptom: Very low audio. Missing audio on slot 4

Recapped audio section to fix low audio issues. Replaced a bad 74LS244 on the top board to fix the missing audio on slot 4. Installed a new battery per owner's request.


Symptom: Low audio, replace battery

Customer requested battery change. Installed cap kit and battery. Tested.


Symptom: Work RAM Error

Replaced bad SRAM at location G9 and ran self tests. Audio level was low. Installed audio cap kit and tested. Board would not read any carts. Replaced a corroded 74LS244 on the top board, cleaned the rodent damage, and patched 2 traces. Tested.


Symptom: Very low audio

Installed audio cap kit and tested.


Symptom: Low Audio

Board would not play hardware test tones. Game audio worked, but was low. Installed cap kit to fix audio levels. Replaced bad SM1 ROM to fix the hardware test tones.


Symptom: Crosshatch of death

Removed leaking battery and cleaned board. Repaired 12 bad traces and tested.


Symptom: Constantly reboots with Calendar Error

System was odd in that it would come up with a Calendar Error message then reboot. The reboot was odd since the system should've stayed on the Calendar Error screen. Disassembled system only to find that it worked fine. Tapping the board caused the problem to intermittently return. Resoldered bad connections on the surface mount Work and Backup RAM to fix.


Symptom: Locks up in Attract mode. Sounds stop working at times. Won't keep high scores.

Replaced bad battery to fix score issue. Board would reboot if carts bumped or jiggled. Cleaned the top board and slots then tested.


Symptom: No sound

Reset backup RAM and then had low volume on right channel and no audio on left. Installed audio cap kit. Replaced leaking battery. Cleaned top board and slots then tested.


Symptoms: Carts won't play and Z80 Error

Cart in slot 1 wouldn't play and in slot 2 gave a Z80 Error. Board was described as having "shipping damage" and the battery came off from the spot welded leads and bounced around between the boards.

DIP switch 8 was on. This is the 'pause' switch which caused the game to freeze upon booting and not play any carts. The Metal Slug cart shipped with the board was dirty. This was causing the Z80 Error. Playing with test carts showed the system had garbled sound effects. No traces were damaged. Swapped out the 74LS244 and 245 chips buffering the sound data. No change. Replaced the YM2610 sound chip to fix the sound issue and tested. Cleaned the Metal Slug cart and tested.

Per customer, replaced the battery and missing screws. Replaced 1 PC board standoff that had crossed threads.


Symptom: Video RAM Error $8000, Written 5555 Read 0055

Replaced bad SRAM IC and tested. Board had low audio. Installed audio cap kit to fix audio issue. Cleaned top board & slots. Replaced 2 missing screws, 2 stripped screws, a broken standoff, and a broken mounting foot. Tested system.

The standoff and foot were broken due to insufficient packing in the box.


Symptom: Garbled graphics and text

The top board had corrosion damage from either a liquid spill or rodent urine. Removed 2 74LS245 and 5 74LS244 chips from the top board. Cleaned the board and checked for trace damage. Installed new chips, repaired 3 traces, and tested board.


Symptom: Video RAM Error

Video RAM Error $00000005 Write 5555 Read 5557

Replaced bad SRAM IC at K9 and tested.