How to buy and test Hewlett Packard HP48 Calculators

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Hewlett Packard Calculators are among the most collectible in the world. Sometimes units fail due to misuse or neglect, but many sold on ebay today are still working perfectly after 30 years or more.   Testing calculators before selling them on ebay ensures a good experience for both buyers and sellers. 

The HP 48 series is extremely popular model from the 90's!!   All 5 models below set the standard for Advanced Graphing Calculators, and are still used today by Engineers, Surveyors, Scientists, Educators, and Hobbyists today.  Below you will find some quick facts about the HP 48 calculator, and a brief test and inspection procedure that tests the keys and functions of the calculator. There are similar tests for nearly every HP calculator ever made.
Things to beware of when buying (any) vintage calculators: 1. Buying a calculator that hasn't been tested or that is not powered when the eBay listing picture was taken.
2. Sellers that don't show the actual calculator,
3. Sellers who insert brief or vague descriptions about the condition.
4. Sellers that say: "we dont have batteries to test this" -- most of the time it is often a cop-out for selling defective instruments- the only exception is on the models with custom battery packs ( e.g. HP 97, HP 67, HP 19, HP 10, HP 35, 45, 37, 38 etc...).  Nearly all of the models made after 1980 use common primary cells like LR44 coin cell, AA, AAA, or N-type batteries.

HP 48 Quick Facts:

Power requirement:  3 each AAA batteries (nominal 4.5 Volts DC)
Number of Keys:     49
Hidden Reset:          Under the top right foot on the bottom of the calculator
Weight:                    7.1 oz ( 202 g) without batteries or case
Screen Resoultion:   131 by 64 pixels
Screen type:             LCD

Models covered in this test:
Model     Code Name        RAM      Expansion     Processor
--------------------------------------------------------------
HP-48S      Shorty             32K        N                 2 Mhz
HP-48SX   Charlemagne   32K         Y                 2 Mhz
HP-48G      Alcuin             32K         N                4 Mhz
HP-48G+    Plus               128K       N                 4 Mhz
HP-48GX   Hammer         128K       Y                 4 Mhz

Test

1. Press ON and E at the same time to start the self-test. This loops the following: Processor Speed test, Disp test, IROM,  IRAM.  When the test is completed you will see OK-48.   Press ON and C to reset the calculator and terminate the test.
2. Press ON and D to initiate the system test menu.  Then press E to start the keyboard test.  You will see a prompt that says KBD1. Press each key left to right, top to bottom starting wit A B C D E F G H… and ending with SPC +.  Follow KBD1 OK with ON and C to reset the calculator and terminate the test.  If pressed out of order, terminate and restart the key test.
3. Press ON and D then EVAL.  This starts the IR Loop back test.  Follow IRLB OK with ON+C to terminate test.

Inspect

1. Front is scratch/dent free. (very limited wear)
2. Screen is not bruised or damaged. (may have some use)  
3. Open battery compartment. Insert/remove batteries and check connections for clean contacts (little or no white or green corrosion).
4. Reverse is clean and scratch free.
5. All 4 rubber feet present.
6. Visually check for 4 straight serial pins.


- hudendai