Friden 1166 Circuit Board #3

The logic board in slot #3 of the backplane of the Friden 1166, like the 1160 and 1162 calculators in the series, contains mainly the arithmetic logic unit (ALU) of the calculator, along with logic that directs the flow of data between the counters. The board has similarities to Board #3 in the 1160 and 1162 calculators, but is most definitely not interchangeable with these machines. The circuit board has "1166" etched at the upper right hand corner of the circuit board to make it apparent that the board was only intended to be installed in the 1166 calculator.

This board contains the "three counter" arithmetic architecture that carries over from the earlier Friden EC-130 calculator. The three counters are implemented in custom TTL (Transistor-Transistor Logic) chips in 24-pin packages. Two of the counter chips are made by Texas Instruments, and the other counter chip is an early Friden-manufactured part, produced by Friden's Research & Development Lab. Friden's R&D Lab had cutting-edge, but small-scale production facilities for integrated circuits, and developed the design for the specialized counter ICs used in the Friden 115x and 116x-series calculators, then provided the design to Texas Instruments, who produced volume quantiies of the chips for Friden. During the early production of both the 115x-series and 116x-series calculators, some of the supply for these counter chips was manufactured by the Friden R&D Lab until Texas Instruments could provide the chips.

It's odd to find one of these chips in a Friden 1166 calculator, as it was introduced somewhat later than the 1160 and 1162 calculators, and by the time the 1166 was introduced, it would be expected that TI's output of the counter chips would have completely fullfilled the production needs for the calculators. However, the date code on the Friden chip in the exhibited 1166 calculator is 6905 (fifth-week of 1969, January 27-31), is in the same date range as the chips found in the museum's 1160 calculator, so perhaps this chip was just a left-over, and ended up used on this 1166 as a fluke.

The three custom chips mimic the functionality of each of the three switch-tail ring counters used in the transistorized first-generation Friden 130 calculator that the 1166 is patterned after. The devices have TI part numbers SN1286(A Counter), SN1287(C Counter), and the Friden-labeled 811788 (D Counter, which would be TI part number SN1288) device.

Board #3 contains a total of 26 integrated circuits, mostly DTL devices, with one TTL 7400 Quad 2-Input NAND gate, and the three TTL custom counter chips. The rest of the IC devices on the board are DTL devices made by Fairchild (DTµL 99xxx-family) and Texas Instruments (SN15xxx-family) Along with the ICs, there are 26 diodes, two resistors and four capacitors.

The bare circuit board has Friden Part #7016704 Revision 1, with the completed assembly having Part #7016705.