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CPU Logie Circuit
The CPU has three LEDs located on the upper left. side of the board, DI9, D20, D21 . On game power-
up DI9 and D2I turn On for a moment then, D19 turns Off and D20 starts to blink rapidly. D21
remains On . The system has detected a problem if the fol1owing happens:
CPU Board LED Error Codes
D 20 blinks one time -
D
20 blinks two times -
D 20 blinks three times -
ROM Error U6
RAM Error UB
Custom Chip Failure U9
1. The game stays in Factory Settings or the displays flash "Factory Settings Restored",
This message indicates that the CMOS RAM no longer retains any custom Pricing or Game
Adjustment
settings and has reverted to factory default sett ings . Generally, the following CPU
checks will isolate the cause of the CMOS RAM memory failure. The voltage at pin 28 and pin 26 of
UB should be +5V (game turned On) and at least +4V (game turned Oft). When the voltage drops
below +4V, memory reset occurs. Check the batteries and battery holder. Be sure that the batteries
are good and that there is no contamination on the battery holder terminals.
'Iurn
the game OFF,
and use an ohmmeter to check diodes Dl and D2 on the CPU Board.
Dl should read 0 ohms when
forward-biased and infinite ohms when reverse-biased.
D2
should read
15
ohms when forward-
biased and infinite ohms when reverse-biased.
2. U6 Checksum
ErTOr.
Check chip U6 and its socket for bent pins. Check the socket for cold solder joints .
If
possible swap
U6 with a known good ROM
3. The game displays flash "Time and Date Not Set".
The real time clock is not running. The clock is necessary for the Audits Menu.
If this occurs go
to U.4 of the Utilities Menu and set the time and date .
4. The CPU is dead
When the CPU is dead it is usual1y very difficult to determine the cause. The biggest problem is
that the address and data lines are almost always stuck low or floating.
Check for +5V and ground. Check for a +5V short to ground. Check for solder short or , cold solders
under any chip or socket . Check the latches for activity. There should be square waves about 4V
peak-to -peak on the outputs.
Check that the 8Mhz and 32Khz clocks are running.
If
all else fails,
swap U4, U6 and, U9 one at a time to try to isolate the problem .
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