UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Help needed with

frsimen · 8th Feb 2023, 10:26 pm

Hello Mark,

One problem fixed, still a few more to find, I think.

IC20 should be dividing by 16, so you will need 16 pulses on the output of IC7 to see one pulse on the output of IC20, IC13 will need 8 pulses, I think, to get an output on pin 7, so will take a lot more spins of the wheel to see anything.

The ICs I was referring to are the same ones still. IC4, 7, 20, 13 and 23. You should see pin 6 change for every pulse going in on pin 5 for all of them except IC4, which is arranged slightly differently. For IC4, you should see the change for every clock pulse on pin 15. It's worth checking that all four pins (6, 11, 14, 2) on each IC change state just to confirm that all is well. Pin 11 will change at half the rate of pin 6. Pin 14 at half the rate of pin 11 and pin 2 at half the rate of pin14. The exact number of pulses needed to complete a count will depend on the initialisation values.

You may have found a fault, or you may just need to spin the wheel for a bit longer!

As a bit of a diversion, one further test which will identify if the VCO is actually locking is to switch the Fine Tune switch to INT. If the VCO is locked, the frequency on the display will change as the fine tune control is adjusted. If it doesn't change, or doesn't seem to change in step with the control, the VCO isn't locked. Go back to the OFF position at the end of the test.

Paula

8th Feb 2023, 10:26 pm	#62
frsimen Heptode Join Date: Jan 2011 Location: Croydon, London, UK. Posts: 773	Re: Help needed with - Racal Dana 9081 Hello Mark, One problem fixed, still a few more to find, I think. IC20 should be dividing by 16, so you will need 16 pulses on the output of IC7 to see one pulse on the output of IC20, IC13 will need 8 pulses, I think, to get an output on pin 7, so will take a lot more spins of the wheel to see anything. The ICs I was referring to are the same ones still. IC4, 7, 20, 13 and 23. You should see pin 6 change for every pulse going in on pin 5 for all of them except IC4, which is arranged slightly differently. For IC4, you should see the change for every clock pulse on pin 15. It's worth checking that all four pins (6, 11, 14, 2) on each IC change state just to confirm that all is well. Pin 11 will change at half the rate of pin 6. Pin 14 at half the rate of pin 11 and pin 2 at half the rate of pin14. The exact number of pulses needed to complete a count will depend on the initialisation values. You may have found a fault, or you may just need to spin the wheel for a bit longer! As a bit of a diversion, one further test which will identify if the VCO is actually locking is to switch the Fine Tune switch to INT. If the VCO is locked, the frequency on the display will change as the fine tune control is adjusted. If it doesn't change, or doesn't seem to change in step with the control, the VCO isn't locked. Go back to the OFF position at the end of the test. Paula