"Michael Black" wrote in message
...
"Alfred Lorona" ) writes:
Does anyone have a schematic for a Ramsey CT-125 frequency counter? Mine
crashed and I'd like to revive it.

Thanks. AL


Open it up, and see what's in side. It will likely be one of two routes.
Either it's going to have a lot of TTL, a decade counter/latch/decoder
for each digit (and possibly 7490/7475/7447), and a divider chain made
up of a string of decade counters. Or it's going to have a large IC that
does all or most of the work, something like the Intersil 7208.

If it's the first case, you can look up any schematic from 20 to 30
years ago, and get the basic wiring. There may be small changes
but it will be fairly constant. Or pull out a TTL databook, and you
will get the functions of the pins. The real variation will be on
the input circuity, ie the analog stuff before it's converted
to TTL, and the reset circuitry.

If it's a large IC inside, then find the datasheet and again
you will have most of the schematic. There will be much less variation
in this case, since the wiring is pretty fixed.

Once you have this basic information, then you can trace to find out
what's not working. Figure out the time base, and make sure it's
outputing properly. Maybe in either case, the analog circuitry is
at fault (after all, it faces an uncontrolled environment, when it's
hooked up to outside circuitry), you can always feed its output
with a TTL oscillator in the HF range, in effect inject a signal,
and if the counter reads out the right frequency, you know where
the problem lies.

Michael VE2BVW


Of course you could always contact "RAMSEY" to get the information straight
from them! I'm sure they have it on hand. They are online! C.L.