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Old 25th Nov 2020, 9:50 pm   #21
PETERg0rsq's Avatar
Join Date: Jun 2009
Location: St Helens, Lancashire, UK.
Posts: 556
Default Re: Racal Dana 9916 Frequency Counter.

Have you looked at the data sheet for IC 1 (74247!) on the display board.

This may give you a clue as to what likely is wrong?

On digital circuits you never see sawtooth wave forms, especially not 12mV!

TTL is 5V or 0V.

What is the BI input (IC1 pin 4 on display board) for, and what does it do?

The data sheets will help you understand what is supposed to happen, and so you can work out what is wrong when it doesnt happen.

If you do not understand the data sheet (not everyone is experienced with logic circuits I know) I will be happy to go through it with you.
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