What is an HP1858-0054 transistor array?

I am working on the reset circuit of an HP9816 computer. The output side is rrlatively conventional, but it takes an input from a chip that I can't identify. The chip is a 16 pin DIL package marked with the HP house-number 1858-0054. That's not in my equivalents list. The chip seems to have been made by RCA, and tracing the connections to it show that 2 of the pins are grounded, but none of them go to any power line. I susepct it's a transistor array, therefore (HP1585-xxxx numbers tend to be transistor arrays too). I've unsodered the chip, but trying to work out the internal arrangement is non-trivial, partly because there seem to be parasitic diodes, and secondly because I am not convinced it's just transistors brought out to the pins. There may be a long-tailed pair, for example. It doesn't match any of the arrays in my RCA databook. As I said, it's on the main processor board (the big board at the bottom) of an HP9816 computer. It's U115 on this board, at the front left corner, just behind the 16MHz clock oscillator can. Does anyone have any suggestions as to what it might be? Anyone have an HP9816 with this IC labelled with somethign other than an HP house number? -tony