[time-nuts] Opening an Isotemp OCXO
artgodwin at gmail.com
Fri Oct 28 13:03:35 EDT 2016
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 <jimlux at 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
>> 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.
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