Missile Command Multigame -- Trouble shooting guide

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Missile Command Multigame -- Troubleshooting guide

* * * Under Construction * * *

So far the only issues seen with the Missile Command Multigame have been either incorrect installation or general Missile Command board problems. The Multigame kit can only work on a fully functional Atari Missile Command board.

General Missile Command troubleshooting guide

As with most Atari games of this era, the first thing to do when a game is not working correctly it to put the game in self test mode. Refer to the manual on where the self test switch is located.

Game is dead. Test mode only pulses out a series of beeps

The first thing MC will do in test mode is a RAM test. MC uses 8 DRAM chips that are 16K x 1-bit. The RAM test fully exercises the first 512 bytes of the DRAM and if that test fails, it attempts to identify the failing and passing DRAM chips by looking at the failure data. It then takes this data and converts it into a series of pulses to indicate which chips seem good and which chips seem bad. The test uses a low tone for good and a high tone for bad. The codes are shown in the table on the right.

It has been seen that MC can sometimes do a poor job of identifying any failed DRAM chips. While the test over the first 512 bytes is very thorough, it stops after the first failure which can lead to misleading results. Also the design of the DRAM circuit is lacking pull-up resistors on the DRAMs. This means a failing DRAM what is not driving its output will leave that data bit floating which also contributes to misleading data. It should be noted if the self test does not pass the RAM test, that there is a very high chance one more DRAMs are bad, however, it may not correctly identify them.

The Multigame self test improves the identification logic and performs additional testing to more accurately report the good DRAMs versus the bad DRAMs. The Multigame also will test the entire 16K bytes versus just the 512 that the original MC self test does. The result is improved fault identification. The Multigame self test also uses both audio and visual indications to pulse out the pass/fail DRAM codes. The screen will change colors, Green for pass, Red for fail while the tones are being pulsed. The original MC tones are also preserved. Low tone indicates a good DRAM, high tone indicates a failed DRAM.

Beep Number	Suspect BAD ram chip
1 (D7)	P4
2 (D6)	N4
3 (D5)	M4
4 (D4)	L4
5 (D3)	K4
6 (D2)	J4
7 (D1)	H4
8 (D0)	F4

Sounds are wrong (or missing)

Missile Command produces sounds using a single pokey chip (40 pin IC at chip location N/P/8/9 near the DIP switches). The pokey chip usually has the text "CO-12294" on it. The pokey chip is a custom chip made by Atari.

If the sounds are incorrect, distorted, it is possible the pokey chip is bad. If you have no sound at all, it could be the pokey, it could be the audio pre-amp on the board, or it could be the external audio amp on the AR II board.

The standard Atari Missile Command self test will perform a simple pokey diagnostic and report the result. A failed pokey is indicated on the upper left side of the screen with the text "CHIP BAD". The diagnostic only tests the random number generator function of the pokey, but it does provide some indication if the pokey is bad.

The Multigame self test performs the same random number generator test on the pokey, but the results are indicated in a different place on the screen.

Pokey chips are used on many classic Atari gameboards including Centipede, Millipede, Asteroids Deluxe, Missile Command, Crystal Castles, and many more.

We have replacement pokey chips should you need one here.

Missile Command test mode screen
showing faulty Pokey

Multigame test mode screen
showing faulty Pokey

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