Gamry Instruments Reference 3000 Operator's Manual page 55

Power LED
USB LED
When the Reference 3000 is first turned on, the Power LED glows steadily for a second or two, blink three
times, and then go to its normal steady blue output. Each blink in this sequence indicates successful completion
of a portion of the Power PC's power-up self-test routine.
A Reference 3000's Power LED blinks when that instrument is selected in the Framework's Instrument
Manager. This allows easy identification of a specific instrument in a MultEchem system without looking at the
instrument Serial Label on the bottom of the instrument chassis.
When the Power LED is off, one of the following is true:
The rear-panel power switch is off.

There is no DC +24 V supply connected to the rear panel DC Power In connector.

The external DC power supply has no input power or is malfunctioning.

One part of the Power PC's power-up self-test has failed.

Caution:
have passed. It therefore cannot be relied on as a true power-status indicator. Always unplug the DC
Power In connection if you suspect your Reference 3000 is malfunctioning.
Panel Indicators and Connectors – Front Panel
The Power LED is used both to indicate power status and that power-up tests
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Cell On LED
Overload LED