Wild_Bill wrote in message
...
This model is a factory assembled model, and wasn't available as a kit,
AFAICT.

Dual counter A-B, single 8-digit LED display (7-segment LED green or red
digits).

Input A 5Hz-175MHz
Input B 5Hz-2MHz

The Input B doesn't show a count when a signal is applied.

The Input A section seems to operate as it should.

I've seen that the actual circuit section for Input B does have an output
signal which is connected to the main board at J103.
I can also see that the counter/display IC is getting good signals at the
correct pins.. input A and B, and control.

Some repairs were made by previous owner, it seems, such as replacement of
the original Frequency Counter/Timer display driver U20, with an
ICM7226AIJL
(high reliability ceramic).

I first assumed that someone may have applied over-voltage(s) to the input
channels, and smoked the counter/display driver IC, but I've seen random
numbers displayed as I probed around the area of IC18 and the
counter/driver
IC, which indicates that the unit can display readings for Input B (no
signal applied to Input A), but the displayed count is incorrect and
inconsistent.

An Intersil ICM7226A/B application/datasheet was included with the counter
unit, and found to be installed in the unit.

The ICM7226 is capable of 2 inputs A & B, and up to 100MHz as a
multi-function (frequency/period) counter and 8 digit display driver.

http://www.nostalgickitscentral.com/...hkit_test.html

The the counter/driver IC, and a circuit IC U18 CD74HCT86E (quad 2-input
Exclusive-OR), and possibly one other support IC may have been replaced.

There was evidence of what appears to be probe-skid-type, or tool
scratches
on the bottom of the board in the area of the input circuitry section of
Input A.

The majority of the ICs are Hitachi, and a couple are Motorola and RCA
devices.

A third BNC input connector located on the rear panel is labeled TOTALIZE.

Another aspect that I'm unsure of is one of the functions.. there is a
selection of FR as one of the unit's functions, and since there is already
one marked FREQ, I think FR represents something else.

The other functions a

PER (period)

TI (time interval?)

TOTAL (totalize)

CHK (check display and indicators)


wb_wildbill-AT-yah-oh-oh.com

--
Cheers,
WB
.............



FR = Frequency Ratio ?
My guess , corroded switch contacts