Thursday, August 27, 2015

HP-21 Calculator

Picked up this HP-21 calculator at a yard sale.DSCF3670 DSCF3671 Plugged in and it doesn’t seem to work and the display is not refreshing quickly.DSCF3673 Power adapter is putting out what I think is the correct voltage more or less.DSCF3681 DSCF3682 DSCF3684 DSCF3687 Batteries looked ok, but are probably bad.DSCF3690 With the batteries out (something you’re not supposed to do) the calculator display is stable but pressing buttons does nothing.DSCF3694 Removed two rubber feet and the screws underneath.DSCF3695 Careful prying separated the halves. DSCF3698 DSCF3700 DSCF3703 DSCF3705 DSCF3707 The board interconnectors are pretty neat.DSCF3708 DSCF3711 So this is a problem (corroded and lifted trace)DSCF3714
And this as well…  DSCF3717 DSCF3718 More corrosion.DSCF3720 DSCF3721 DSCF3723 DSCF3724 DSCF3725 DSCF3727 DSCF3728 DSCF3731
So I’ll have to see about removing all of the corrosion and rebuilding the broken traces. I hope I won’t have to desolder any of the ICs but some of the corrosion runs underneath. Fun!