--- In hp_agilent_equipment@..., "arthurok" <arthurok@...>
wrote:
does the unit use a 5 volt power supply?
one trick would be to build up a circuit to divide a
crystal osc down to 5 hz
i think a 7492 is a divide by 12 counter.
7490 is divide by 10 in ttl
More informations on the schematics:
The logic power supply is +5V (more exactly 5,1V according to the
manual), the logic is TTL (not ECL) but the function of the I/O pins
is not totally trivial.
The decade divider chip 1820-0098 picks up its 100Hz input with a
capacitor coupling just behind the 155V high voltage rectifier.
The chip has an input pin and divide by 10 output cascaded to another
divide by 10 chip, a reset input, plus a couple of less obvious pins:
I named them control input and controlled output.
The controlled outputs from the two cascaded dividers are connected
together directly and to the Clock input of the counter Main Gate JK
flip-flop.
The control pins are connected to the gate time selector switch that
can ground one or the other divider's control pin.
The logic appears to be: grounded control pin => controlled output is
active divide by 10 output, else controlled output is high Z.
So I guess I could effectively replace this chip with a modern decade
divider such as a 7490, a logic OR and an open collector transistor.
My main option is still to try to find a spare chip ...
-Marc-
