Hi Gerald!
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Do you have any service adapters?
Do you have the Extended Service Software SRAM Card?
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Or could you open the Duplex, Output and FEX unit, leave the unit on the side with a good look into the unit while running.
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Wait until the unit is cold, power it up, check that all LEDs on the open boxed are going off after a few seconds.
Play around with the thing and wait until the error appears. Report which LEDs got lit.
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Background is that there are multiple signals checked on BIT tests. These are logically or-ed into one fault signal per box. The LEDs are on some of the detailed lines and some only on the combined output.
To be able to locate the LEDs, some pictures or card and name of LED would be helpful.
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73 de DC3AX
OE3UPR / DC3AX