Occasionally the DELL SX280 Optiplex booted with a BIOS warning "time-of-day" not set. Because the SX280 came from long-time storage, it wasn't really surprising for this to happen. The internal battery was probably depleted. After installation in The Machine the BIOS message came more often, so it was time for a quick CMOS battery replacement. But as usual the battery replacement wasn't that easy after-all.
The DELL Optiplex SX280 uses a common cr2032 lithium battery to remember it's BIOS settings in CMOS memory and to keep the internal clock running. The battery mounted somewhere on the motherboard usually last for several years.
The BIOS of the SX280 checks CMOS during startup and can trap a stopped internal clock. The factory date of the SX280 clock apparently is 30 march 2007 - 11pm. This value is the default BIOS value when there's no recent date available.
With a fresh CR2032 battery the SX280 occasionally comes up with this screen;
The "Time-of-day clock stopped" message seems to appear only in the morning after a night of down time.
And that's only occasionally, roughly once every 2 weeks.
|The location of the CR2032 battery / button cell in the DELL SX280 Optiplex - underneath the SATA hard disk frame
With the CMOS battery being perfectly ok, it seems there's a different problem. Till now the issue is unresolved. Months later the problem did not occur again, and had seemed to resolved itself somehow.