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The 3B2 computers have a pair of LEDs on their front panels, one green and one amber/red. When system problems crop up, the 3B2 may give a hint by flashing these LEDs, and this table summarizes what those LEDs mean. This is taken from the 3B2 Maintenance Reference Manual.
|1 amber/red pulse||Unknown Problem: the console may be wired incorrectly or there may be other trouble not revealed by LED pulses. Investigate further using diagnostics.|
|2 amber/red pulses||Problem with CPU|
|3 amber/red pulses||Problem with firmware (ROMs)|
|4 amber/red pulses||Problem with RAM. Possible bent pins in backplane (usually where system baords plug into backplane), defective I/O boards, or any hardware failure that may cause a problem with memory access.|
|5 amber/red pulses||Problem with the DUART (console serial port)|
|Both green and amber/red LEDs on||Reseat memory boards, I/O backplane. Remove feature cards. Try to reboot. Disconnect battery and reconnect (to clear CMOS), then reboot. Swap first memory card.|