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#1
02-02-2020, 10:27 AM
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Power supply filter symptoms in 50Hz sets
I've got a mid-60's Sony that someone has replaced one of the 500uf filters with two 470uf in parallel at some point in the past. The set has a fairly pronounced hump about 2/3 of the way down the screen where it all bends to the left and then back. It occurs to me that since the power line frequency and the vertical sweep frequency are both 50Hz, it's likely that a filter-related bend like that won't crawl up the screen as it does on NTSC sets on 60Hz power.
Is that right? A bad filter will manifest as a bend that doesn't move? 
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#2
02-02-2020, 10:57 AM
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Correct.
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#3
02-03-2020, 07:03 AM
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Great thanks
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#4
02-03-2020, 08:29 AM
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The grid fequency is not constant. It varies up and down by small amounts. Hence a hum bar can run slowly up or down the screen in 50Hz countries. In less developed countries the grid frequency may vary more widely.
I've not had experience of seeing hum in 60Hz countries but I guess it usualy moves in one direction because the nominal field frequency is 59.94Hz. (60/1.001) The grid frequency would have to be unusually low for visible hum to move the other way.
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#5
02-04-2020, 02:23 AM
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Right, it's a bar that moves gradually up the screen then starts over at the bottom.
The one on the set I'm looking at now is stationary pretty much, aside from a couple times I thought "is that a bit lower than it was?". After a recap I suspect it will clear right up. Then I can go on to track down why there is no RF AGC voltage. And why there is no audio. This set is more fun than a barrel of monkeys!
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