For more than a year I was searching the Internat for an obsolete IC that's used in a Motorola S1344AAB Frequency Counter/Auto Tune Deviation Meter. The Motorola part number 51-80329A60 is actually a DM85L52 manufactuerd by National Semiconductor (the IC is stamped 528 055178). I was able to get the data sheet from a friend that had an old NS data book from the early 80's. The part is a decade counter/latch with tristate outputs and will cause readout or counting problems or an incorrect frequency display. The counter also uses a DM85L51 that crosses to a
74LS173.In the early 70's the unit was Manufactured by Systron Donner for Motorola. Systron Donner's model number was SLN6407A-75. They also manufactured a frequency counter model 6252 that's identical to the counter section of the 1344AAB. Other SD frequency counters, like the 6250 or 6202 use the same part.
If your looking for that part and you don't want to spend hundreds of dollars buying a minimum quantity from a surplus dealer, Look for any of the above SD models on Ebay. If your lucky and get one for about $25, cannibalize it for parts.
Jack WA9FVP