Author Topic: SNK Games (Neo Geo MVS/AES) (Read 126206 times)

channelmaniac · « **Reply #60 on:** May 23, 2014, 09:03:19 PM »

Model: MVS MV-4
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.

channelmaniac · « **Reply #61 on:** May 23, 2014, 09:03:29 PM »

Model: MV-4
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.

channelmaniac · « **Reply #62 on:** May 23, 2014, 09:03:37 PM »

Model: MV1
Symtpom: Audio cuts out

The audio would get very low and sputtery sounding at intermittent times. Board had a cap kit already installed. Narrowed it down to a dirty Stereo/Mono selector switch. Cleaned the Stereo/Mono selector switch and tested.

channelmaniac · « **Reply #63 on:** May 23, 2014, 09:03:45 PM »

Model: MV4
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.

channelmaniac · « **Reply #64 on:** May 23, 2014, 09:03:54 PM »

Model: MV4
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.

channelmaniac · « **Reply #65 on:** May 23, 2014, 09:04:04 PM »

Model: AES
Tip: Diagnosing RAM problems

The AES is different than the MVS in that it does not display error messages on the screen if there are hardware problems. To diagnose problems, boot the system without a cartridge installed. The screen will turn different colors depending on the errors.

Blue = All tests passed
Red = WorkRAM error ($100000 region)
Green = PaletteRAM error ($400000 region)
Yellow = VideoRAM error
Pink = Bios selfcheck error ($C00000 region)
Cyan = Memory card error

The AES tests will only test the memory card if it is inserted and it is blank. It does NOT test the Z80 or other parts of the sound subsystem.

Many thanks to the folks at the neo-geo.com forums for this list!

channelmaniac · « **Reply #66 on:** May 23, 2014, 09:04:13 PM »

Model: MVS-2F
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.

channelmaniac · « **Reply #67 on:** May 23, 2014, 09:04:21 PM »

Model: MV1C
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.

channelmaniac · « **Reply #68 on:** May 23, 2014, 09:04:30 PM »

Model: AES
Symptom: Needed custom BIOS installed

Customer wanted the system upgraded. It had the old Debug BIOS stacked on top of the AES BIOS chip.

Removed 1 resistor and the double stacked chips. Installed a new socket and a freshly programmed UniBIOS chip. Board would not boot. The UniBIOS file supplied by the customer was corrupt.

Programmed another EPROM with the UniBIOS 2.3 code and tested.

channelmaniac · « **Reply #69 on:** May 23, 2014, 09:04:39 PM »

Model: MV1C
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.

channelmaniac · « **Reply #70 on:** May 23, 2014, 09:04:48 PM »

Model: MV4FT2
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.

channelmaniac · « **Reply #71 on:** May 23, 2014, 09:04:58 PM »

Model: MV2F
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.

channelmaniac · « **Reply #72 on:** May 23, 2014, 09:05:06 PM »

Model: MV4
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.

channelmaniac · « **Reply #73 on:** May 23, 2014, 09:05:15 PM »

Model: MV4
Symtpom: Audio cuts in & out

Installed an audio cap kit and tested the board.

channelmaniac · « **Reply #74 on:** May 23, 2014, 09:05:27 PM »

Model: MV4
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.

channelmaniac · « **Reply #75 on:** May 23, 2014, 09:06:23 PM »

Model: AES
Symptom: No sound

This was a bear to track down. Cleaned corrosion off the board. Cleaned the right end pins on each slot and socketed 3 chips to check the traces under them. Found a bad trace between E9 pin 6 (74LS11) and CN4 (front slot) pin 47A and Q3 pin 9 (74LS04). This trace was the Chip Enable pin on the sound program ROM. Patched the trace and tested the board.

channelmaniac · « **Reply #76 on:** May 23, 2014, 09:06:32 PM »

Model: Ikari III - The Rescue
Symptom: Garbled graphics a lines on the screen

Checked the board for damaged traces then started checking the video SRAM with the well calibrated finger. Found one (and received a blister on the finger) that was internally shorted. Found another one hotter than the others and checked it with a logic probe. It had bad looking signals on the data lines. Replaced both SRAM ICs and tested the game.

channelmaniac · « **Reply #77 on:** May 23, 2014, 09:06:40 PM »

Model: MV1
Symptom: Z80 Error

Swapped the Z80 chip with the proper Z80A. No change. Inspected the board closely and found some corrosion on 4 pins of a surface mount IC connected to the Z80 CPU. Continuity tests showed one trace was open. Cleaned the board and soldered in Kynar jumpers pm all 4 corroded traces to repair it.

Only one was needed to do the repair but by doing all 4 the board will last a lot longer for the customer.

channelmaniac · « **Reply #78 on:** May 23, 2014, 09:06:49 PM »

Model: MV2F
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.

channelmaniac · « **Reply #79 on:** May 23, 2014, 09:06:56 PM »

Model: MV4
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.

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Author Topic: SNK Games (Neo Geo MVS/AES) (Read 126206 times)