I post this here because I could not find this solution anywhere on the internet.
For those of us that still have an old HP 48 lying around, be aware that the survey card and RAM card each have an internal battery that need to get charged every month or so. As it turns out, the HP 48 only supplies a charge to these cards when it is turned "ON".
Yesterday I decided that I wanted to try to use the HP 48 for a little project. I have a TDS survey card loaded and a RAM card. I turned on the 48 and discovered that it couldn't read or see the survey card or RAM. After multiple tries and a walk through the internet, I learned that I needed to charge these card batteries. This sounds simple enough, but the internet gurus all said I needed to charge these cards for at least 24 hours. The HP 48 automatically turns off after 10 minutes of no activity.
The solution to overcome this 10 minute "off" problem is to set an alarm for every nine minutes. First thing is to put fresh batteries in the HP 48. The HP has two types of alarms. The first is an appointment alarm which beeps and wants to be turned off. The second is a "control" alarm. A control alarm executes a command. You'll want to set a control alarm, as follows:
With the calculator on, hit the "shift right" button, then the "time" button.
This brings up the alarm window, select "set alarm"
In the message window enter any command such as <>, be sure to use the double arrow key to create a command. This command does nothing but keep the calculator on.
In the time window, select a time a few minutes in the future.
Set the date.
In the repeat window, set it to repeat every 9 minutes for a GX, 4 minutes for an SX
Press "OK"
This should keep the HP 48 turned "ON" so the card batteries get a charge. After 24 hours. Return to the alarm screen, "Browse alarms" and "Purge" to cancel the alarm. The cards should now be charged and ready to be re-installed. You do remember how to do that, right?
