Wild_Bill wrote:
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

Do you have a copy of the schematic that you can post somewhere on the web
so we can take a look at the circuitry? Otherwise, it's just a shot in the
dark.

--
David
dgminala at mediacombb dot net