Cpu Board Test

RUG PATTERN. At power-up, a scanning "rug" pattern appears on the game's screen. During this display, the game checks Video RAM chips. These include Video RAMs U42 through U49 and U68 through U75. A stationary, striped pattern replaces the scanning rug. This pattern is an artifact of the testing process. (It reproduces the last two lines of the rug pattern stored in Palette Latch U13/U30.) Since DMA U77 loads the Video RAM, the test also demonstrates DMA condition.

CPU BOARD DRAWING. Following the stripe pattern, an assembly diagram of the CPU Board appears very fleetingly. This diagram indicates test passage by Video RAM chips checked during the rug pattern (above). Also tested is main microprocessor (GSP) U18. Other tested components include Scratchpad RAM (U60 through U63) and Color RAM (U7/U41). The game checks CMOS RAM U65 too. As they check good, the screen depicts the chips in green. Bad chips appear in red.

BAD CHIP NUMBERS DISPLAYED. If the game finds an error, you'll see the message "RAM ERRORS DETECTED. PRESS ANY KEY TO RETURN TO MENU." Normal games display the message "NO RAM ERRORS DETECTED. PRESS ANY KEY TO RETURN TO MENU."

LED INDICATOR. If RAM damage is extensive enough to prevent a screen display, examine the CPU-Board LED-indicator. The game attempts to display bad chip numbers (digit by digit) here too. The error code on the indicator corresponds to RAM chip number. This code appears one character at a time. The code begins with "E" for error. The next two digits refer to the chip number of the first bad chip detected. Corresponding chip numbers are screened on the game's CPU Board. {NARC games display these letters and numbers upside-down.)

If the game displays a RAM error; check the indicated RAM's DC power voltage...

• 4461 DRAMs: Positive five volts on pin 12 (ground at pin 24).

• 4464 DRAMs: Positive five volts on pin nine (ground at pin 18).

None of these pins should have more than a few millivolts of AC on it. Never replace a RAM chip until you prove that these voltages are normal!

RAM Power Pins

RAM Power Pins

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