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Old 16th Sep 2019, 2:59 pm   #56
peter_scott
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Join Date: May 2003
Location: Edinburgh, UK.
Posts: 3,273
Default Re: Yet Another Bush TV22

Very many thanks for all your thoughts. I haven't pursued them all yet but I think I have eliminated faulty or wrong value components around the frame oscillator.

Looking at waveforms wrt ground I can't see any movement in the frame output drive or anode but if I look on the secondary of the output transformer then (wrt ground) the wiggles are clear to see. The osc. transformer is original and I don't think it has ever been removed since manufacture.

I did try removing the C34 2uF electrolytic mounted on the scan coils but this made no difference to the wiggles. It appears to simply straighten the top lines of the scan when in circuit.

Disconnecting the signal the timebase free runs and appears to still be interacting with the interfering mains.

I did wonder if the HKS transformer could be affecting the frame ECL80 that it is mounted next to so I put an aluminium sheet between the two but couldn't see any change.

I don't think the HKS could be leaky because primary and secondary are side by side in separate partitions of the plastic former.

Yes Jac, holding my finger on the grid of the output valve does give an accentuated version of the fault.

Shorting the triode grid to ground I can't really see any wiggles.

Thanks to all,

Peter

Last edited by peter_scott; 16th Sep 2019 at 3:07 pm.
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