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Old 7th Feb 2023, 9:37 pm   #58
frsimen
Heptode
 
Join Date: Jan 2011
Location: Croydon, London, UK.
Posts: 767
Default Re: Help needed with - Racal Dana 9081

Hello Mark,

I've checked the diagram again and I was wrong. Pin 1 of IC7 is not connected to the other pin 1s, so what you have measured is correct.

The pins I listed for IC20 are incorrect, I should have said to check on pins 14 and 2, both should be at 0V. I muddled up the pin numbers on the diagram.

The C11/R33 measurement is not correct, so that deserves more attention. Check that C11 is the correct way around firstly. I think you have fitted a new one already, so I hope that is a good component and not leaky. Also check that you measure 220k from the negative leg of C11 to chassis. A cracked track, bad joint or faulty R33 could all cause the problem here.

You could try turning the tuning spin wheel a few turns and look for pulses from pin 7 of IC4. You should see several pulses as it is turned. Move along to pin 7 of IC7 and look for pulses t should be 0V.there. They won't be as frequent as the ones from IC4. If you see that, move along to IC20 pin 7 then IC13 pin 7. The pulses will be further apart as you step along the IC chain. If nothing else, that should prove that the N counter is working. If you look at the output pins 2,6,11 and 14, you should see them changing state on the counter ICs as you tune.

I'm a bit puzzled though. If all the other measurements were as stated above, why is the frequency not settling in the mid range and why is the limits circuit complaining? I'm not sure the battle is over yet.

Paula
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