APC UPS Overload light blinking and constant alarm tone


I have a Back-UPS XS 900 on a standalone Debian server that seems to randomly start sounding a constant overload alarm, even with nothing plugged in. The alarm continues to sound until I manually turn the unit off. Additionally, nothing seems to be logged when the alarm starts to sound.

Here is the output from apcaccess while alarm is sounding an nothing is plugged in. The BATTDATE should actually be 2007-07-05, but apcaccess is reporting it incorrectly (the correct value is returned if I query it in apctest). The only difference appears to be that STATUS changes from ONLINE to a blank value.

APC      : 001,038,0925
DATE     : Sat Dec 05 16:37:38 MST 2009
HOSTNAME : kamui
RELEASE  : 3.14.4
VERSION  : 3.14.4 (18 May 2008) debian
UPSNAME  : kamui
CABLE    : USB Cable
MODEL    : Back-UPS XS  900 
UPSMODE  : Stand Alone
STARTTIME: Sat Dec 05 16:22:24 MST 2009
LINEV    : 117.0 Volts
LOADPCT  :   0.0 Percent Load Capacity
BCHARGE  : 094.0 Percent
TIMELEFT : 557.7 Minutes
MBATTCHG : 5 Percent
MINTIMEL : 3 Minutes
MAXTIME  : 0 Seconds
SENSE    : Medium
LOTRANS  : 088.0 Volts
HITRANS  : 139.0 Volts
BATTV    : 25.4 Volts
LASTXFER : No transfers since turnon
TONBATT  : 0 seconds
CUMONBATT: 0 seconds
STATFLAG : 0x07000000 Status Flag
MANDATE  : 2007-07-05
SERIALNO : [removed]
BATTDATE : 2145-00-36
NOMINV   : 120 Volts
NOMBATTV :  24.0 Volts
NOMPOWER : 540 Watts
APCMODEL : Back-UPS XS  900 
END APC  : Sat Dec 05 16:37:48 MST 2009

I have already tried it without anything plugged into it and with the server alone. I have also used a Kill A Watt to measure the outlet voltage and it measured 117.4 V when I tested it and the alarm began to sound.

Is there anything else I can check?

EDIT: The lights that show up when this happens is the blinking red overload light and nothing else.

Best Answer

I had a MOSFET failure on my APC RS-1000 with the same observations as yours:
Overload light and constant alarm even when nothing was wired on the outputs.

They changed the board (rather the entire unit) and retained the batteries which were still functional.
Uh, I had some hard time working this out with the APC Service though. That was not exactly stellar.