I know that pressing and holding [ON] and pressing and releasing [/], and then releasing [ON], the keyboard test is started in the HP-15C. With [ON] and [x] is possible to test the calculator and display functionality.
Similar and more complete tests exist in the HP-48SX.
It could be usefull to me and to all the HP collectors to know how to perform these test in all the other HP models, to test a calculator before pay for it. Could anybody help me ?
Thanks. (I think it is a good info for the Collectors Corner of the HPMuseum)