Intermittent black squares printing from Pioneers to 82240B

[Joe Horn]

Could the problem be that the IR LED in your 27S is too LOW, rather than too close, relative to the printer's IR receiver? Try raising the calculator a tiny bit (e.g. by resting it on a thin booklet), until its IR LED is at the same height as an HP 48's IR LED. I vaguely remember HP recommending that.