Hi april, sorry for the late reply, I was repairing a batch of 15 computers .
Do the other digits still work properly? Select various frequency bands on the FT-7B to verify that the first digit (tens of thousands) changes. This will confirm that the 74LS196 is ok.
I suggested earlier that you set up the counter to work without the metal chassis so you can measure the voltages under the board. You could solder a wire to the ground of the circuit board and wrap the other end around the negative probe of your meter so you will have one hand free and a solid ground.
I have also been looking into the possibility of invalid data at the input of the MSM561RS. Some display decoders blank the display when the input data is invalid (greater than 9 , binary 1001) like 4511.
The 7447 decoder has a RBI (ripple blanking input) pin that blanks the display when it is L (logic 0) and the input is zero (LLLL). This removes leading zeros for example, 14.5 is displayed instead of 00014.5.
This may be the function of pins 14 and 15: pin 14 is open and pin 15 is H (5v) for Q8 to Q12, pin 14 is grounded and pin 15 is open for Q13 (tens of thousands).
I would be my pleasure to get your counter working because equipment like this lasts for years unlike the modern micro-controlled disposable equipment.
If you have two transistors and light emitting diodes, you can build a simple logic probe that would make testing easier. Use red and green leds.
Timescope
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