Sharp IS501 OPIC

I havea shaft encoder here in a classic (well, it's over 10 years old :-)) printer. And it seems to have failed in that I am getting no signal at all on either output line (they should be quadrature signals, of couse). They test as floating.. I've taken in apart (of course, what have I got to lose...) and the PCB cotnains a Sharp IS501 OPIC device along with a couple of resistors conencted to it, a supply decoupling capacitor and a limiting resistor for the IR LED. THe latter seems to be working (dropping about 1.5V). but no outputs. The IS501 is a 6 pin stagered-DIP transparent package. The 6 pins are +5V, gorund, the 2 outputs and the 2 (sensitivity?) resistors. So not much I can so other than replace the chip. A qucik web search turns up nothing useful (and no data sheets). Anyone ever come across anything like this before, knows a substitute, etc? -tony