Apple II+/IIe will not power on.
Replace 22ohm resistor & nearby small electrolytic cap in power supply - common problem on the non-Astec model supplies.
Apple IIe/II+ will not power on. Power supply tests good.
Check for shorted capacitors on the +12v line and replace.
Apple IIc/IIe has garbage on the screen
Common problem on these. Press Ctrl-Open Apple-Closed Apple-Reset to run diagnostics and replace the defective IC shown on the screen.
Apple IIc floppy disk will not spin or read. Drive tests good.
Replace defective IWM (Integrated Wozniak Machine) IC. This controlls the floppy disks.
Commodore 64 gives nothng but a blank screen - reset line on CPU is stuck
Found a short between the 7406 IC and the metalized cardboard RFI shield. Attached a thin piece of posterboard to the shield with double-stick tape and trimmed the pin on the IC.
Commodore 64 gives nothing but a blank screen
Found multiple machines with this symptom: Replaced bad VIC II chip on one, replaced a bad PLA chip on another, Replaced a bad 74LS629. Could also be caused by a defective crystal.
Commodore 64 shows screen & border, but no text
Ran into different causes of this. One machine had a defective 4164 RAM IC, another machine had a defective PLA, and another a bad Character ROM.
Commodore 64 has bad text colors
Replaced a defective 2114 SRAM IC. This IC is responsible for the text colors.
Commodore 64 has missing keys when typing
Commonly this is caused by dirty switches on the keyboard. If it is a single key or multiple keys that aren't in a pattern, then press them repeatedly for a few minutes to let the self wiping contacts clean the switch. If the keys are in a row or column then replace a defective 6526 CIA chip.
Commodore 64 won't read/write to/from the serial port
Replaced a bad 6526 IC.
Commodore 64 has missing or stuck audio
Replaced defective 6581 SID chip.
Galaga3 has a garbled title on screen
Checked the ROMs and PROMs on the board for proper checksums. Programmed 2 new 82S131/63S241 PROMs to replace 2 PROMs that were for the Gaplus game and not the Galaga3. The title was Galaga3 but the colored outlines were for Gaplus.
Galaga3 is dead
The power supply board had 2 problems. First battery on the power supply board had leaked and corroded quite a few components. The second was a blown 3/8 amp slo-blo fuse that someone had replaced with a 7 amp (!!!) fuse that blew as well. Replaced a cracked 10 ohm 5 watt resistor, 1N4001 diode, a shorted 4.7uf tantalum capacitor, and the LM305 voltage regulator. Cleaned the circuit board and replaced the corroded components as well. Set the 5v line to 5.15v and tested the game.
Kangaroo monitor only shows a white screen
This was an old WG 4800 series monitor. Replaced a shorted zener diode and blanking transistor on the input daughterboard. While the board was out a cap kit was installed and all cracked solder joints were fixed.
Neo Geo AES error screen info
The Neo Geo AES system has built-in diagnostics that give different color screens depending on the test results.
Boot the system without a cartridge and make a note of the color on the screen:
Blue = All tests passed (The AES does not test the Z80 sound IC).
Red = Work RAM error (0x100000 region).
Green = Palette RAM error (0x400000 region).
Yellow = Video RAM error (programmed through custom port).
Pink = BIOS selfcheck error (0xC00000 region).
Cyan = Memory card error (only tested if card in unit and blank).
Neo Geo MVS 4 slot system doesn't recognize cartridges
The 74F138 (3 to 8 decoder) at location A2 was missing a signal on an enable line which caused the chip's outputs to never go active. Repaired a broken trace on the board to repair.
Neo Geo MVS 4 slot system only works with slot 3 and 4.
The 74LS138 (3 to 8 decoder) IC at location A2 is responsible for the decoding of the slot enable line. Pin 2 was stuck high. Traced that back to the 74F174 at A1 and there was no signal on that chip. Fixed a broken trace between A1 and C4 to repair.
Neo Geo MVS System - diagnosing 4-slot SRAM locations
When reading error messages such as:
Written AAAA Read AABA
The AABA can be broken down into upper and lower bytes. AA is upper, AB is lower, and each byte is handled by a separate SRAM IC.
On the NEO-MVH MV4 (4 slot) board these are at the following locations:
- Upper Backup RAM: D9
- Lower Backup RAM: F9
- Upper Video RAM: L9
- Lower Video RAM: K9
- Upper Work RAM: H9
- Lower Work RAM: G9
Neo Geo MVS System - diagnosing 6-slot SRAM locations
When reading error messages such as:
Written AAAA Read AABA
The AABA can be broken down into upper and lower bytes. AA is upper, AB is lower, and each byte is handled by a separate SRAM IC.
On the NEO-MVH MV6 (6 slot) board these are at the following locations:
- Upper Backup RAM: E9
- Lower Backup RAM: F9
- Upper Video RAM: L9
- Lower Video RAM: K9
- Upper Work RAM: J9
- Lower Work RAM: H9
Neo Geo MVS system gives Backup RAM error
A four slot Neo Geo MVS gave a Backup RAM error: Address 00D00000; Written 5555; Read 0000. Battery corrosion on the board ate up a trace between the 10k resistor next to the battery and the 74HC32, pin 13 at location D10. This was causing a loss of a signal at pin 20 (/S) on the 256K SRAM chips. The loss of the signal meant the chips would not enter the write cycle.
Neo-Geo MVS system gives Bank 1 RAM error message
Replaced the CXK5864 SRAM ICs. If the message was Bank 0 then the LSPC IC needs replacing as that RAM is inside the IC.
Neo-Geo MVS system gives Main CPU RAM error message
Replaced the two 62256 SMT (Surface Mount Technology) SRAM ICs connected to the CPU. This error message could also be caused by bad traces on the board.
Neo-Geo MVS system gives Video RAM error message - address $0000
Replaced the 62256 SMT (Surface Mount Technology) SRAM ICs. Bad traces on the board can also cause this error.
Neo-Geo MVS system gives Video RAM Error at address $8000
Replaced CXK5814 SRAM ICs and tested board.
A second board with the same error had a corroded plated through hole on a trace between the SRAM and the LSPC IC. Jumpered the trace to fix the problem.
Neo-Geo MVS system gives work/backup RAM error message
Replaced 62256 SMT (Surface Mount Technology) SRAM ICs. These RAM chips are the ones with pin 24 connected to the backup battery for power. Defective traces on the board have also been found to cause this problem.
Neo-Geo MVS system gives a Z80 Error message
This one is tricky. Cleaned the cartridge edge and cartridge slot. This did not fix it. (Some carts have the sound ROM on the cart and a bad connection will give this error) Replaced the Z80 CPU to fix.
Error could be caused by the Z80, Sound ROM, 6116 SRAM IC, NEO-257 IC, NEO-G0 IC, or they YM2610 sound IC. Basically any problem that causes the sound system to appear unresponsive will give this error.
Neo-Geo MVS system has garbled video
Neo Geo 2 slot board worked and passed all RAM tests but video was messed up. The normal title screen was squished up into the upper half of the screen. The bottom half of the screen was a jumbled mess. During gameplay things on the screen changed on the upper half and bottom half at the same time.
Replaced one CXK5814 IC. IC tested fine on self tests and on an external tester. It had an internal addressing issue where the top addressing line had failed. When addressing the top half of the chip it would restart at the bottom of its memory. It would pass the simple memory tests of the Neo Geo and the external tester. Replacement of the chip cured the video problems.
Neo Geo MVS has missing audio sounds
This 4 slot system took a lot of troubleshooting to fix as it could've been any IC in the sound subsystem. Certain sounds were missing while others were fine. Replaced a bad 74AS244 at location R1 to fix.
Neo Geo MVS system is dead - has clicking from speakers
This system powered up but never appears to start its self tests. The clicking sound from the speakers meant that the watchdog circuit was resetting the CPU in an attempt to kickstart the system. Replaced the lower work SRAM IC to fix the board.
Neo Geo MVS system is dead - no clicking from speakers
This system powered up but never finished self tests. The missing clicking sound from the speakers meant that the watchdog circuit wasn't resetting the CPU. Found that the bottom board had bad battery corrosion damage. Removed the battery, cleaned up the damage, and checked the work and backup SRAM ICs with a logic probe. Found the /write signal missing on the lower backup SRAM. Patched the bad trace and replaced the battery.
Neo-Geo MVS system runs but will only display a white screen
Neo Geo 4 slot top board would only display a white screen with the "Insert Coin" and "Credit 0" text visible and that text was misspelled too. Sound and program ran normally.
Replaced 74LS244 ICs at locations N4, J4, E4, and A4 to fix. These are all tied together and a short in one will take out the other three.
Neo Geo MVS System shows crosshatch and won't recognize cartridges
Neo Geo MVS 4 slot gives a crosshatch pattern on the screen. Won't recognize any cartriges. The problem was 4 corroded traces going to connector CN10 from a nearby leaky backup battery. Ran jumper wires from CN10 pin B5 to B9 pin 18; CN10 pin B6 to B9 pin 3; CN10 pin A5 to B7 pin 2; and CN10 pin A6 to B7 pin 3 to fix.
Pit Fighter game controls are not working
Replaced bad 74LS244 ICs at locations 70B and 75B. Tested board.
Pit Fighter has garbled graphics
Swapped IC S30 with a parts board to fix. Burned a new GAL for the parts board.
Pit Fighter has no video output
Traced the video signal back to the output latches. Signal was on the input side but not crossing the IC. The clock signal was missing. Replaced the GAL at 65D to fix.
Pit Fighter loses most sounds after heating up
Most audio signals disappeared after playing the game for about 10 minutes. Cooling spray had no effect. The audio signals would come & go. Sometimes they would work but most of the time they wouldn't. IRQ lines were going dead when the sounds disappeared. Replaced the 6502A CPU on the sound board to fix.
Pole Position II is dead - garbage video
Replaced the two big blue capacitors in the bottom of the cabinet, resoldered the broken pins on the power supply/audio boards connectors, and set the 5v line for 5.05v at the game board. Now the game powers up & tries to run, but has garbled graphics.
Pole Position II runs but has garbled video
Put the game in test mode and found that the video RAM was bad. Replace 2 2148 SRAM chips and had fun playing the game.
Rally Bike has garbage video
The screen was black with a small section of garbage characters on it. Board would make the coin up sounds when the coin mechs were triggered. Looked at the board carefully and found a corroded pin on a capacitor. This corrosion went down into the PC board and ate an internal trace. This disconnected power from 2 ROMs. Removed the cap, cleaned up as much of the damage as possible, and ran 2 jumper wires to fix the game.
Sega Turbo Out Run is dead
Lights were on for the video board but not for the CPU board. Replaced burned power connector and adjusted power supply voltage to 5.05v.
Sega Turbo Outrun is missing obstacles and backgrounds
This was a strange one. The sky and road obstacles were missing. The buildings were there but the road and the car never moved left or right. This was a problem with the subprocessor. Built-in tests showed one of the ROMs bad. ROM read good in an EPROM programmer and a replacement ROM gave the same symptoms. Checked all the pins on the socket for continuity. The ROM pairs (High & Low) had a common CE line. This was driven by a 74LS138. The chip had badly rusted legs. Replaced the chip and the game worked normally. The rust had travelled up the body of the chip.
Sega Turbo Outrun has no sound
Resoldered the internconnects and the audio output IC.
Street Fighter 2 has no video - sounds work
Replaced a bad 74LS00 and 74LS74 on the ROM board. Replaced a corroded socket and an EPROM with a broken leg. Game now gives video but has no sync - this will be looked at another day.
TI-99/4a powers up but is dead
Checked the Address Bus lines with a logic probe. Some were stuck low. Replaced defective ROM IC.
TRS-80 Color Computer has nothing but @ on the screen
Computer was a 64k version. Owner had moved jumpers on the board causing +12v and -5v to be applied to the RAM. (Jumpers were used to reconfigure the sockets for 16k or 64k DRAM ICs) Reset jumpers to correct position and replaced all 8 4164 DRAM ICs.
TRS-80 Color Computer keyboard is not working correctly
TRS-80 Color Computer is missing rows or colums of keys - replaced a bad PIA IC.
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