How do I charge the internal battery of a 72A series DAS?
CPU Battery: The CPU board has a 2.4 volt back-up battery to retain CPU RAM when the DAS is powered off or asleep. This battery also powers the Perpetual Time Clock of the CPU under those same conditions. When external DAS power is available and the DAS is turned on, this battery is recharged via the 5 volt Vcc. The Vcc voltage is constantly monitored. If Vcc falls below 2 volts the monitor chip switches RAM and PTC circuits over to operate from the back-up battery. If ever the back-up voltage becomes very low, the contents of CPU RAM are lost and the DAS reverts to sleep mode with acquisition set to ‘STOP-OFF’. The initial indication of a low back-up voltage is that DAS time becomes erratic and eventually defaults to 1988:001:00:00:00:000 – this occurs at about 0.4 volts. RAM content and timing accuracy are guaranteed to remain intact as long as the back-up is 2.0 volts or more. Experiments have shown that the RAM can remain intact down to 0.3 volts, but this is not guaranteed. These
