wolfievtec
Member
I have a 1979 Flash that has some issues. The game plays but I have no sound. The test button on the sound board works when I press it. I sent the main board and driver board out for repair so I know they work. Any ideas? Thanks.
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Sound Board Basics - Its Own Computer.
All versions of the System3 to System7 sound boards operate in the same manner. The sound board is basically a stand-alone computer. Its brain is a 6802/6808 CPU chip, and also has a single 6810 static RAM chip, and its own 6821 PIA (Peripheral Interface Adaptor) chip, and a 2716 or 2532 EPROM which holds the program code. There is a reset section just like the main CPU board, and the boot up process for the sound board is very similar to the boot up process for the main CPU board.
For example, pin 40 of the 6802/6808 CPU chip is held low at power-on for a moment while the +5 volts stablizes. Then the CPU reset pin 40 goes high. There is a clock signal at pins 38,39 of the 6802/6808 that also must be running, from the 3.58 mHz crystal. If the CPU chip's pin 40 is high, and the clock is running at CPU pins 38 & 39, the program code stored in the sound board's EPROM is run (assuming all the address and data lines are present between the CPU, PIA, RAM and EPROM).
The sound board also has its own +5 volt power supply. The transformer supplies 12 to 18 volts AC to the sound board connector 10J1, which goes through a small bridge rectifier and a filter capacitor. Unregulated +12 and -12 volts DC is produced in the process. The unregulated +12 volts goes to a 7805 voltage regulator, producing a regulated +5 volts DC just for the sound board. Remember there are also one or two fuses on the sound board for the incoming AC power.
Sound Board Test Works, but Missing Sound in Game.
Sometimes there will be a problem where the game is powered on, sound test button pressed, and all the sounds (and speech) work. But in game mode the sounds don't work. Usually this is a 6821 sound board PIA problem, or maybe a 6810 problem. But here's some things to try:
Verify with a logic probe that the 5 signal lines to the sound board are all pulsing low when cycling through solenoid tests 9-13.
Grounded each signal pin at the sound board and see if sounds are produced.
Measure the associated pins on the 6821 when you're grounding pins on the sound board connector pins.
Check sound board IC6 pin 13 (4068). It should pulse high whenever you ground a pins on the input connector.
Check sound board chip 6821 pins 37/38. If it's working, the /IRQ will go low when you ground input pins.
Example: Pinrepair user K.Nelson had a Gorgar that was missing two sounds in the game, and that played the wrong sounds during game play. Using the game's solenoid test he found solenoid sounds 9/10 were not working. Yet pressing the sound board's red test switch played all sounds.
To make sure the driver board was not the problem, he ran a jumper wire from the driver board solenoid9 connector pin to one of the sound board inputs he knew was working. And sure enough, the game triggered this sound no problem in the diagnostic sound test. So he knew the problem was on the sound board. Turns out after replacing the 6821 PIA on the sound board, the problem was fixed.
Great info tool guy..
I've got a Firepower with some sound problems.. I'll pay a little more attention to the 6821 PIA ,is that common issue for these?
Is it mostly the chip or the sockets?
VB,