SNK Games (Neo Geo MVS / AES)

[channelmaniac]

Model: All MVS boards
Troubleshooting Backup RAM Errors

If you see this for a Backup RAM Error:

Code:

Backup RAM Error:

Address    Write  Read
00D00000   5555   0000

Then you have a different problem all together.

This is caused by the chip not being selected properly for read/write access. This is almost always (well, I'd say > 99.5%) a problem with the chip or with the trace that is controlling the SRAM and NOT with the SRAM.

Look for broken traces whether from battery leakage or someone scraping something across the board which physically damaged the traces. If that's not it then trace back the chip control traces to see what chip is feeding it.

On the 32k x 8 SRAM ICs (the 62256 or equivalent) that are used for the Backup, Work, and Video RAM that would be:

Code:

Pin 27: *write (also known as *WE) - Write Enable
Pin 22: *G (also known as *OE) - Output Enable
Pin 20: *E (also known as *CE) - Chip Enable

OK, OK... the * in front means it is an active low signal. If it's high, it's not being signaled. If you get NO signal from your logic probe on one of the pins then you have an open trace for sure.

Pin 20: should always be grounded on the Work RAM and Video RAM. That pin is directly connected to ground and if it isn't then you have a physically damaged trace. On the Backup RAM it is used to put the chips into low power standby mode.

Pin 22 & 27 connect to different chips. These are the ones you are most concerned with when troubleshooting this type of problem. Follow the traces and repair corroded or otherwise damaged ones. (99.5% of the times this is the fix)

Oh, when troubleshooting these you WILL have to strip off the red cardboard and the black foam under the circuit board in order to follow the traces. Have fun cleaning all that crap off. Yuck.

[channelmaniac]

Board: MVS MV-2
Backup RAM locations

When diagnosing the Backup RAM problems on a NEO-MVH MV-2 2-slot board:

Upper Backup RAM location: H3
Lower Backup RAM location: H4

[channelmaniac]

Model: MVS MV1FZS
Symptom: Crosshatch of Death

This board does not suffer from the same battery damage induced Crosshatch of Death as the old style 4 slot board.  The old-style 4 slot board's problem is one of legendary status and it should be documented that it is the ONLY board to consistently suffer from that kind of problem.

Powered up the board and duplicated the symptoms. Looked for obvious signs of damage and found where the bottom of the board was gouged by something. Repaired 3 broken traces connecting to the cartridge slot resolve the crosshatch problem and repaired another 3 broken traces causing corrupt video.

Always check the boards you are working on for signs of physical damage. It's pretty common on arcade boards.

[channelmaniac]

Model: MVS MV-4F (newer style 4 slot)
Symptom: Z80 error and rapid audio click

Had a MV4F board that came in with a Z80 error and a rapid clicking sound in the speakers. Strange thing is that as the speakers clicked the picture on the monitor flickered.

(Little did I know this thing would kick my ass.)

Replaced the Z80 CPU to fix the Z80 error. For some reason SNK put a Z80 in there and the board is labeled for a Z80A (higher speed) CPU.

Now the system booted but flickered like mad. Audio ouptut was horribly distorted.

With the audio down the system worked fine except the audio output IC was getting very hot. Recapped the audio section. No help. Replaced the audio output IC. No help. Replaced the volume control. No help.

For some reason there was an oscillation happening in the audio circuit. This oscillation was causing the audio output IC to suck up large amounts of current. This was causing dropouts in the +12v output of my bench supply. These dropouts matched the screen flicker and the clicking of the speakers.

Checked every trace in the audio section - all were good. Replaced the 3 op-amps. No help. Checked all the film caps (the non-electrolytic caps)... all checked good.

All voltages looked OK but were a little lower than another MV4F board but they were within reason (+12v was a little low so the other voltages around the chip were correspondingly lower)... On a whim I removed both of the .1uf film caps on the speaker outputs. Audio was distorted but amplifier was stable.

Next I put them back in circuit one at a time. The one on the right speaker was the cause of the problem. Replaced the cap and problem was still there. It looks like there's an issue with the ground trace inside the board. Removed the cap and ran the board for an hour at 3/4 volume with no problems.

[channelmaniac]

Model: MVS MV-4F
Troubleshooting reset lines

In working on a 4 slot board (MV4F) I encountered a Z80 error.

The board had other issues (documented elsewhere) and when those were fixed and the board not yet reassembled, it gave a Z80 error.

The reset line was held high.

The reset line goes through the 74AS245 IC at location E11. It goes through the latch on pins 2 and 18. If that IC is bad the reset line could be stuck high or low, causing the Z80 CPU to never boot.

That reset line must transistion from low to high to reset the Z80 CPU and make it start executing commands.

In this case the problem came because the IC at E11 was pulled from the board as a step in troubleshooting. Once the IC was placed back in the board the reset line cycled normally and the Z80 booted. (This was also tested by jumpering the reset line on pin 15 of IC A9 to pin 26 of the Z80 before replacing the IC)

[channelmaniac]

Model: MVS MV-4F
Symptom: Stuck in Watchdog (Click of Death)

Have a 4 slot board in to repair that was giving the click of death - stuck in watchdog - problem.

This can be caused by many different problems, including:

Bad CPU
Bad Work SRAM
Bad Backup SRAM
Missing control signals on Work or Backup SRAM
Shorted 74AS245 ICs buffering program ROMs on top board to CPU on bottom
Short on address bus
Short on data bus
Missing address or data signals to chips

First thing... Check for gouged traces. Found and fixed one. No effect.
Next... Substitute BIOS. Nothing.
Next... Check control signals on the Work RAM - Stuck high on pins 22 and 27.
Next... Check control signals on the Backup RAM - Stuck high on pins 22 and 27.
Next... Check control signals on the BIOS ROM - These were working.

So we had a problem somewhere in the system to where it was trying to read the BIOS but not able to initialize hardware.

Pulled the 74AS245 ICs buffering the data lines to the top board. Had no effect.

Checked for more broken traces. No more were found.

Checked the address and data lines going to the BIOS and SRAM ICs. All were good. Checked the data lines going to the NEO B1 chip. All were good. Checked the data lines. All were good.

Next checked the A22* and A23* alternate lines. Missing one one! Ran a jumper wire from Pin 55 of the NEO-E0 IC to pin 117 of the NEO-B1 IC and the board came up!

OOPS. Z80 Error. Reset line stuck high. On a Z80 since the reset line did not transition from low to high the Z80 never booted. Ran a jumper and the audio section worked. Replaced the pulled 74AS245 ICs and the board wouldnt' boot. Reset was stuck low.

Turns out the reset line for the Z80 CPU and chips on the left side of the board goes through the 74AS245 IC at E11. Removed the jumper for the reset line and board booted normally.

Plugged the top board back in, inserted some test carts and played a couple of games.

[channelmaniac]

Model: MVS MV6
Symptom: Vertical lines in graphics

Some background objects had vertical lines in them - in this case the "shock Troopers, 2nd Squad" floating logo had lines. It's the logo that is on the screen when it is playing in demo mode. I traced it to connector CN8 and started tracing it on the bottom board.

UGH. It goes straight to NEO-CT0

As one final step before replacing that surface mount chip I checked the continuity between the top board and bottom. Bingo! No continuity. Next step - pull the boards apart and look at the connectors. They had something sticky on 2 of the pins and up in the socket.

Desoldered and disassembled the socket then cleaned the pins on both connectors. Reassembled, resoldered into place, and tested. Board is fixed.

Moral: Don't discount those board connections! Look at them closely to see if there is a foreign substance in there causing the problem.

[channelmaniac]

Model: MVS MV4F
Symptom: Video RAM Error

This board had multiple problems due to liquid damage.

4F board came in with a Video RAM error. Replaced the upper Video RAM IC and error went away but video was glitchy and had bad colors.

Repaired a bad trace between the lower Video RAM IC and the LSPC2 IC.

Glitching was gone but the colors were bad. Test screen showed blank for red, blue for both blue and green, and white was a little off color. Put in a UniBIOS chip and noticed the green was off and the low end of red was missing AND a white block was in the place of the lowest red color. (SNK BIOS shows 4 color boxes, one for each color. The UniBIOS chip shows color spectrum bands for each color)

Checked the Color RAM and noticed that address line A2 was stuck low. Checked the NEO-B1 IC and noticed that A2 was stuck low there as well. Backtracked through the circuit and found that the TDI4 pin (pin 22 - signal name P16) was floating - no signal.

Checked the other ends of the signal - the 74LS245 IC buffering the L0 ROM and pin 134 of the LSPC2 IC. They had signals. The trace under the LSPC2 connecting to pin 134 was bad. Ran a jumper wire between the 74LS245 and the NEO-B1 chip to fix. (It was WAY easier to solder to the big pin on the 245 than the small one on the LSPC2!)

Audio was missing on one channel. Grabbed the oscilloscope and found that the volume control was bad. Replaced it with one off of a parts board.

Reassembled the game and tested. Slot 3 had vertical lines on the screen through graphics. Patched a corroded trace to fix. Played a few games to test.

Replaced the leaking battery then reassembled the board for one final test.

[channelmaniac]

Model: MVS MV4F (newer smaller 4 slot)
Symptom: Missing/Garbled sound problem.

This board has been a pain to track down. The board had been worked on before  by another tech.

Fixed a broken trace on pin 15 of IC 4N (74AS245 - other tech damage - grrrrr!) and the board would play sounds but was distorted on the higher frequency digital music.

The sound ROMs are read through the YM2610 IC through data latches (74LS245) at board locations 2M and 2N. If the voice and lower frequency music notes are distorted then replace the IC at 2M. If the higher frequency music is distorted, replace the IC at 2N.

On this board the replacement of 2N did not fix it. Board had a damaged trace internal to the board and the ground pin on IC 2N was not connected. Ran a patch to fix the board.

[channelmaniac]

Fixed: AES
Symptom: Lines in overlay graphics (text, health, etc) and no sound

Fixed a corroded trace leading to NEO-B1, pin 131, from the cartridge slot to restore the video.

Looked at the YM3016 Sound DAC and there was no serial clock or data flowing from the YM2610 sound chip. Checked the Z80 CPU and it appeared good. Looked at the clock signal on the YM2610, pin 63, and it was dead. Traced it back to a 74AS04, pin 1 near location K4 and found a corroded plate thru hole on the trace. Patched the trace to finish the board repair.

[channelmaniac]

Fixed: AES
Symptom: Garbage on screen

Swapped out the Video RAM (62256 surface mount) chips and system would then give a yellow screen indicating a video RAM error. Checked the VRAM with a logic probe and saw that the address lines were pulsing regularly and were not pulsing erratic indicating they were being used when the system would run the Video RAM tests.  Data lines, CE*, and W* lines appeared to be working normally. Checked the pins on the LSPC2 and found address line A1 was not pulsing with data. Traced it back to the BIOS chip and found the upper pad missing from the address line A1 pin.

Ran a short jumper to fix the board.

When someone replaced the BIOS on the console with the UniBIOS chip they socketed it, but not before pulling the upper pad and platethru removing the old chip.

[channelmaniac]

Fixed: AES
Symptom: No video, would play blind

Repaired bad trace on pin 126 of the NEO-B1 IC to fix the video clock and bring back the video.

Fixed a bad trace on pin 125 of the NEO-B1 IC to fix a graphics corruption problem.

Board played for about 10 minutes then rebooted to a red screen - bad Work RAM. Replaced the surface mount 62256 SRAM at R6 to bring it back from the dead. Finish the repair by running the game for a half hour to burn it in.

From the last couple of repairs it appears that the AES suffers from the same random board corrosion problems that some of the MVS boards do. Some of the boards weren't cleaned very well at the factory and gunk left on them would eat random traces.

[channelmaniac]

Resurrected: AES Parts Board
Symptoms: Dead, multiple cut traces, no video out.

Had a complete parts board (no missing chips or damaged SMT chips) that was dead. Multiple solder bridges, traces cut, and missing the daughterboard.

Installed a replacement daughterboard and patched 3 cut video (RGB) traces. Patched a broken trace connecting to pin 112 of the PRO-CT0 chip. Removed multiple solder bridges. Board would then try to boot but was stuck with garbage on the screen. Shorting out 2 data lines would result in a watchdog reset. No W* or CE* activity on the video RAM but did have activity on the work RAM and the system BIOS ROM. Board was trying to boot but never making through self test enough to put a color on the screen indicating what RAM was bad.

Replaced the work RAM at R6 and the board would then boot to a blue screen with no cartridge plugged in indicating system's RAM was working properly. The video output was distorted and would fade in and out during the self test. Checked the CXA1145 RGB Encoder chip for broken traces as that chip looked to have been replaced before. Found a break between the pad and trace on Pin 13 (I REF connection.) Patched the trace to fix the video.

Board would then boot and run but had connection problems with the cartridges. The slot connectors were very loose - basically worn out. Replaced both connectors (100 pins per connector!) with ones pulled off of a parts board to fix the slot problems.

Unit had a Japanese BIOS. Swapped that out for a European BIOS and socketed it.

Board played until it got hot then would randomly reboot. Board would also reboot when tapped or flexed. Used an eraser attached to a #2 pencil to just barely touch each pin on the NEO chipset chips and found the LSPC-A0 IC was the culprit. Resoldered the IC then was able to shake and tap the board without it rebooting. Let the board play for an hour to test.

[channelmaniac]

Model: MVS MV-2F
Symptom: Audio would cut in & out

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

[channelmaniac]

Model: MVS MV4
Symptom: Audio would cut in & out

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

[channelmaniac]

Model: MVS MV4
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.

[channelmaniac]

Model: MVS MV-4F
Symptom: Lines in background AND foreground graphics. No audio but board would make popping sounds and the screen would flicker with the pops.

Board had strange graphics corruption on foreground and background graphics. This was different than what is normally seen as evenly spaced lines (1 bad line showing up out of every 8 bits across the screen) and instead was like every other line was missing.

Swapped top board out and narrowed problem down to the bottom board. Checked the 74xx245 buffers between the top and bottom board. No problems found. Put the board under the magnifying lamp and found shorted pins from pin 65 to pin 80 (65 through 76 are ground pins anyway) on the NEO-ZMC2 IC at location 11M. Resoldered the pins to fix the graphics problem. Installed an audio cap kit and reset the backup RAM to finish the repair.

It appeared to be leftover solder from when it was factory soldered that finally bridged the trace between pin 79 and 80. There were solder blobs between every pin down that side of the chip but only 79 and 80 appeared to be shorted.

[channelmaniac]

Model: MVS MV-2F
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.

[channelmaniac]

Model: MVS MV-2F
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.

[channelmaniac]

Model: MV-6 (6 slot)
Symptom: Bad Video RAM and graphics corruption

Battery leaked and caused corrosion on the board and it had a Video RAM error at $8000 - Written 5555 Read 5FFF.

Replaced and socketed both CXK5814 ICs to fix the Video RAM error. Removed the battery and cleaned up the corrosion some. The board would work but then had a funky video problem.

This wasn't a normal vertical line through the images type of problem. It looked like horizontal lines through all images. It started with overlay graphics, moved to foreground moving objects and then on to backgrounds. It also got worse as the board heated up.

Resoldered the NEO-B0, PRO-C0, and LSPC surface mount ICs. This helped some but not much.

Running a finger across the board would cause the problem to get worse if you touched the area around the 74HC32 IC at C6. Replaced that IC but it had no effect.

Broke out the component cooler and sprayed the PC board under each chip around the 74HC32 and found that the clock driver IC, a 74LS368 was bad. Spraying it with component cooler immediately fixed the graphics problems until the chip heated up again.

Replaced the chip and played a game of Shock Troopers 2nd Squad.

[channelmaniac]

Model: MVS MV2 (older 2 slot)
Symptom: Lines in foreground (player) AND background objects

On the 2 slot Neo Geo boards the NEO-257 ICs are the 2 to 1 multiplexer ICs that choose which slot to get the graphics data from. There are 3 of them on the board. If one of these is bad then there will be lines in the graphics elements they are selecting. Top left is background graphics, bottom left is player graphics, and the one on the right side is for text and other overlaid objects.

Replaced both of the left side NEO-257 ICs and the corruption was still there. Logic probe showed that the data was coming in and exiting the NEO-257 ICs correctly but I thought that maybe they were garbling the data. Nope. Problem still there.

Did some further tracing down to where the data goes to the NEO-C0 chip. It flows from the 257s through the ZMC2 IC and then on to the C0 chip.

Replaced the NEO-ZMC2 IC and tested the board.

[channelmaniac]

Board: MVS MV4
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.

[channelmaniac]

Model: MVS MV4
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.

[channelmaniac]

Model: MV2
Symptom: Backup RAM Error

Board would get to the green screen then reboot. This was a constant repeating cycle. Flipped all the dip switches to run the system through a Backup RAM test. It gave a Backup RAM error with the message Written: 5555 Read: B240

(The B240 error is stuff of legend over on the Neo-Geo.com forums.)

Checked the Backup RAM with a logic probe and found pin 20 (CS*) was dead on both. Traced it back to the 74HC32 and back to the battery backup circuit. Traces were good. The resistors and diodes in that section were good. Checked the C1815 transistor with an ohmmeter and it was OPEN from collector to emitter. Replaced the transistor and the board booted right up.

I have to say this is the first time I've seen an open transistor that wasn't blown in pieces. I think the corrosion from the battery must've traveled up the legs and into the body of the transistor and caused it.

[channelmaniac]

Model: MV2F
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.