Phoenix Repair Logs
Repairer: Paul Swan
BOARD NO: 0077
No ship explosion or shoot sound. Other sounds O.K.
IC5 and IC6 (LS374) are the sound control latches. Using a logic probe to map out which circuit contributes to what sounds gave the following results:-
IC5 (Data outputs)
pin 19 -> Barrier tone (Bit 0)
pin 2 -> Barrier tone (Bit 1)
pin 16 -> Barrier tone (Bit 2)
pin 5 -> Barrier tone (Bit 3)
pin 15 -> Alien hit explosion
pin 6 -> Bird wow-wow
pin 12 -> Music select
pin 9 -> Music on
IC6 (Data outputs)
pin 19 -> Alien swoop/hit tone (Bit 0)
pin 2 -> Alien swoop/hit tone (Bit 1)
pin 16 -> Alien swoop/hit tone (Bit 2)
pin 5 -> Alien swoop/hit tone (Bit 3)
pin 15 -> Alien hit explosion
pin 6 -> Alien swoop
pin 12 -> Ship fire
pin 9 -> Ship explosion
Both the ship fire and explosion circuits were fed from a linear feedback shift register (IC46, CMOS 4006) that was in turn clocked from a NE555 oscillator (IC42). The oscilator was switched by TR1. Using a logic probe verified that TR1 was working correctly and pin 3 of IC42 was oscillating as was pin 3 of IC46. The outputs of IC46 taken at pins 8 and 9 were stuck high. These two outputs feed a an XOR gate (IC22, LS136) the output of which is inverted and fed back into pin 1 of IC46. The schematic for this circuit seemed to suggest that it was possible for this LFSR to "lock-up" if all the shift register latches end up all-one, and using a pulse injector on pin 1 of IC46 to add a few zeros into the LFSR chain started the sounds off and the LFSR maintained itself from then on. Power cycling the board always seemed to result in the LSFR locking up. Since this seemed to be a "design fault" rather than a circuit fault, I examined some of the other LPN Phoenix board sets and these had a modification on them to insert zeros into the LFSR at power on as follows:-
Wire link: IC9 (8085) pin 3 -> IC28 (74LS05) pin 5
Wire link: IC28 (74LS05) pin 6 -> IC29 (74LS05) pin 9
It looks as if this was a "field" modification and it isn't a particularly "neat" solution but it does seem to work.
Symptom: No video. Whining sound from speakers
The board was stored someplace where it got wet & had what looked like leaf residue on it.
Cleaned the bottom board and replaced all 12 ROM sockets. Replaced the K1 and K2 EPROMs as they had pins that rusted off at the body.
No change. All ICs appeared dead. There was no clock signal. Replaced a bad 7404 IC to fix the clock. Game would boot but had garbage on the screen and would randomly reboot.
Replaced 1 74LS244 IC and 1 2114 SRAM ICs that had corroded legs. The rust on the 2114's legs went up the pin into the body of the IC.
Played a few games to test the system.
Symptom: Graphics glitch and bad audio
Replaced missing sound pot. Board was missing the shooting and explosion sounds. Replaced a bad 4006 IC at IC45. Replaced bad socket on ROM at location IC23 to fix an intermittent graphics glitch and tested board.
Logic probe showed the clock signal and video sync signals were present. It also showed no activity on both the address and data busses. Replaced a bad 2114 SRAM IC to fix. Replaced broken sound pot to fix the audio output.
Symptom: Dead. Missing 3 chips and 17 capacitors. Has 2 pulled traces.
Obvious trace damage on board - 2 traces were sticking up from the board and there were 2 missing pads on IC17. IC17 was also missing. The CPU socket was partially melted from a soldering iron.
Replaced missing IC17. Patched 2 broken traces. Replaced bad CPU socket and replaced the missing 8085 CPU. Replaced broken IC48 on the video board.
Replaced 17 missing capacitors and 1 incorrect resistor to fix the sound subsystem.
Symptom: Board sync output is bad
Board had some kind of output on the sync pin but it was incorrect. Found that the board was modified. 1 trace was cut and 2 were jumpered. Reset the board back to factory, replaced the broken sound pot, and tested.