The 1k resistor doesn't seem to feed the 'S30'. It looks as though pin 14 (Vcc) goes via that thick track to the +12 input.
On Fri, Oct 28, 2016 at 5:46 PM, jimlux <jim...@earthlink.net> wrote: > On 10/28/16 8:31 AM, Peter Reilley wrote: > > Looking around with my scope it seems that the output driver chip is bad >> as I expected. It is a TI 14 pin surface mount DIP. It says S30 on it >> which if it is a 74S30 it is an 8 input positive NAND gate. The board >> layout confirms this as the 10 MHz signal is connected to pin 2 and all >> other inputs are tied high. Pin 8 is connected to the output. >> >> The chip is run off 12 volts so it must be CMOS. But I cannot find any >> chip like that that will run off 12 volts. Any suggestions for a >> replacement? >> >> Also, using an 8 input NAND chip for a driver seems an odd choice. >> >> > could it be some sort of 74C series? if it's intended to run off 12V, a > lot of the CMOS parts can run at almost any Vdd (a virtue of 4000 series > CMOS - 15V power, no problem) > > Maybe they got a good price on the 8 input NAND parts? > > If unused pins are tied high, it's unlikely that they are outputs - most > parts are either a totem pole or open collector output, neither one of > which would like being tied high. > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
