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Repair Logs

Phoenix (Centuri, Inc) PCB repairs


Tools: schematics, logic probe, soldering iron

Problem: No fire or death (explosion) sound

Solution: Cold solders joints at C34 and R67. Replaced IC 45 a 4006


Problem: The background was not scrolling

Tools: schematics, logic probe, soldering iron and solder wick

After adding support for this version of Phoenix to MAME and setting the scroll value to 0 in the emulation, the emulation acted the same as my board. The scroll memory handler in MAME was set to address $5800. With some help from Chris Hardy, the suspected components were identified, IC 33, IC 35, the #2 ribbon cable connectors at pin 4, and finally IC 8 on the ROM board.

IC 33 is responsible for decoding address $5800, which we found to be the address of the background scroll location from our experiment with MAME. How was this component identified? Good question, I asked it myself, then looked closer at the schematics and parts. The Hexadecimal value $5800 is 101100000000 in binary, this tells me that the address lines corresponding to the bits set in the address are the first place to look for the problem. They are A11, A12 and A14 on the CPU, they connect to IC 33 as inputs on pins A0, A1 and E3 respectively. Looking at the truth table for IC 33, which is a 74LS138 1-of-8 decoder, when all three inputs are high, only the output on pin 12 is high, the rest are low. This means that every time this address is written to by the CPU, these three lines need to be high. Pin 12 of this chip connects to pin 12 of an OR gate in IC 35, a 74LS32. When the input is high, the output on pin 11 should also be high. Putting a logic probe on pin 12 of IC 35, I noted that the pin was pulsing, as it should. Then I checked the output on pin 11 expecting to see the same pulsing, but the pin was always low. Replacing this chip with a $0.89 part from Radio-Shack solved the problem.

Solution: OR gate at IC 35, a 74LS32, had its output at pin 11 stuck low.

Phoenix (T.P.N.) PCB repairs


Tools: schematics, logic probe, soldering iron

Problem: Garbage screen game does not play

Board was populated with incorrect EPROMs. I erased and burned copies of the ROMs in a working board. Game now powers up and runs. NOTE: The EPROMS were 2716s, my working board has 2516 in it. It turns out, this board can run either EPROM type.

Problem: board will not coin up

Traced this one down to a bad 27LS244, the input on pin 2 is connected to the coin input on the card-edge and is pulled low when the coin switch is closed, as it should be, but the output on pin 18 was not pulsing low when the board was coined. Replacing the chip with a socket and new chip fixed the problem.

Solution: Replace 27LS244, IC4


Tools: schematics, logic probe, soldering iron

Problem: Player 2 start button does not work

The input on pin 4 of IC4 is connected to the player 2 switch input on the card-edge and is pulled low when the button is pressed, as it should be, but the output on pin 16 was not pulsing low when the button was pressed. The 47LS244 tested good, so I check the schematics to find where the trace fom pin 16, the output was supposed to connect. It runs to pin 16 on IC1, a 74LS245. There was no continuity when checking it with a meter. Using a magnifying glass, I could see the trace had been pulled up from the pcb at pin 16 of IC4. Soldering a jumper wire between both pin 16s fixed the problem.

Solution: Broken trace between pin 16 of the IC4 and pin 16 on IC1.

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