Galaxian by channelmaniac
Symptom: Large color stripes on screen
Board was missing the U and W ROMs. Burned replacement 2716 EPROMs to bring the CPU to life. Large color stripes would change periodically. The ROMs at J1 and L1 were bad. Burned replacement 2716 EPROMs and the board showed a perfect screen.
Symptom: White screen
Game gave a full white screen and no video artifacts. CPU was rebooting itself and the data lines were in a repeating loop for signals. Replaced bad ROM at Z. Pin 13 was broken on the chip.
Symptom: Bad RAM 2 error message on screen
This error message is related to the RAM at 3F or 3H. Replaced both RAM chips then the board came up with a Bad RAM 3 message. This indicates a bad RAM at 4FH or 5FH. Replaced the RAM at 5FH to fix that error. Board then came up with a Bad ROM message. Reseated the ROM daughtercard to fix that error.
Board then came up with horizontal lines across the screen. Burned a new character EPROM at 1H to fix the lines.
Symptom: Bad RAM 1
This indicates a problem with the RAM at 7N or 7P. Replaced both RAM chips to fix the error. The game had horizontal lines across the screen. Replaced the ROMs at 1H and 1K to fix the lines.
Symptom: Constant background tone when playing
Galaxian is supposed to have a varying tone in the background when playing. It gets faster and faster as the game is played. On this board it was only playing a single continuous tone.
The troubleshooting guide points to a problem with a 555 timer and the 2 GE6015 transistors. The 555 timer had already been replaced by the customer. Checked the 2 GE6015 transistors and they were good.
Checked C15, C16, R15, R16, R17, R18, R20, and R21. All checked good. Swapped the 555 timer chip since it was CMOS and the original part wasn't. No change. Checked the resistance from pins 2/6/7 of the 555 to +5v and ground. It read 1200 ohms to both power and ground. Swapped out the LM324 quad op-amp chip to repair the board. It connected to pins 2/6/7 of the 555 timer chip and had an internal short to power and ground on the input.
Tip: Transistor cross reference
The Galaxian sound subsystem uses 2 GE6015 transistors to oscillate the background audio. These transistors are no longer made and are not in the NTE cross reference book.
They can be successfully replaced with the easy to find 2N3906 transistors.
Symptom: Board had multple RAM failures and no video sync
Replaced U74, a surface mount 74LS07 and replaced a burnt zero ohm resistor on the video ground to fix the video sync problem.
Resoldered U66, U32, U62, and U63 then resocketed U48 to fix the RAM issues and random reboot issues. Board can now be jostled briskly without rebooting.
Reset button was dead. It had liquid (rodent?) damage. Cleaned the board and replaced the switch.
Symptom: No Sync
Replaced a bad 74LS08 at location 6H and tested.
Symptom: Dead. Garbage on screen.
Reseated the ROMs. Address lines were stuck high. Data lines were dead. CPU stuck in watchdog reset. Replaced bad Z80 CPU and tested.
Symptom: Dead
Board had damage from a previous attempted repair.
Board would try to boot but just make beep/blip noises and repeating garbage on the screen. Cleaned the legs on all the ROMs. ROM W on the daughter board had a broken leg. Patched the bad leg and replaced a bad ROM U on the daughter board. Chip at 9B had a pulled trace that needed patching. Patched the trace then replaced a bad 74LS367 chip at 8D. Board would THEN try to boot but had a RAM Error. Replaced a bad RAM chip at 5F. Board then booted but had color stripes on the screen and no stars. Replaced bad ROM at 1H to finish. Tested game.
