HP HP-21 - Seivice; Low Power; Blank Display

56 Accessories, Service, and Maintenance
Note: If you use your HP-21 extensively in field
work or during travel, you may want to order the
optional Reserve Power Pack, consisting of a battery
charging attachment and spare battery pack. This en-
ables you to charge one pack while using the other.
If the battery pack won’t hold a charge, it may be defective. If
the warranty is in effect, return the pack to Hewlett-Packard
according to the shipping instructions. If the battery pack is out
of warranty, see your nearest dealer or use the Accessory
Order Form provided with your HP-21 to order a replacement.
Service
Low Power
All decimal points except the true one light to warn you that
you have a minimum of 1 minute of operating time left.
1.0.0.0.0.0 0.0. Low Power Display
A :
True decimal point
You must then either:
1. Turn the calculator OFF and connect it to a charger that
is plugged into the ac line.
2. Insert a fully charged battery pack.
Blank Display
If the display blanks out, turn the HP-21 OFF, then ON. If
does not appear in the display, check the
following:
1. If battery charger is attached to the HP-21, make sure it
is plugged into an ac outlet. If not, turn the calculator
OFF before plugging the charger into the ac outlet.
2. Examine battery pack to see if the contacts are dirty.
3. Substitute a fully charged battery pack, if available, for
the one that was in the calculator.
4. If display is still blank, try operating the HP-21 using the
charger (with the batteries in the calculator).
5. If, after step 4, display is still blank, service is required.
(Refer to Warranty paragraphs.)