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PJL · 11th May 2019, 11:28 pm

Not much time today but the 100KHz is OK so it's the complicated 36.4MHz oscillator that is the culprit. The scope images match the repair guide and I followed the realignment instructions that centres the control voltage and it quite happily runs at 36.4MHz with a fixed voltage but then runs faster as soon as the feedback connection is restored.

I will have another run through tomorrow to try to understand whats going on by breaking the loop, varying the control voltage and monitoring the frequency and phase comparator output. It's using another double balanced mixer this time with the 4 diodes on an IC. It converts the edge of the 100KHz clock to a pulse then adds ringing at approximately 36.4MHz and phase locks to this. I guess the ringing might be off frequency?

The 36.4MHz oscillator, is only used for the counter and tracking generator and it could have been wrong for a while. There is still the original fault of low amplitude.

11th May 2019, 11:28 pm	#21
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Marconi TF2370 fault fixing Not much time today but the 100KHz is OK so it's the complicated 36.4MHz oscillator that is the culprit. The scope images match the repair guide and I followed the realignment instructions that centres the control voltage and it quite happily runs at 36.4MHz with a fixed voltage but then runs faster as soon as the feedback connection is restored. I will have another run through tomorrow to try to understand whats going on by breaking the loop, varying the control voltage and monitoring the frequency and phase comparator output. It's using another double balanced mixer this time with the 4 diodes on an IC. It converts the edge of the 100KHz clock to a pulse then adds ringing at approximately 36.4MHz and phase locks to this. I guess the ringing might be off frequency? The 36.4MHz oscillator, is only used for the counter and tracking generator and it could have been wrong for a while. There is still the original fault of low amplitude.