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Old 12th Oct 2017, 10:16 pm   #46
Argus25
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Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: My first antique TV-Olympic Model 755-need help.

Quote:
Originally Posted by ms660 View Post
So far as I can make out the sound IF take off is via the anode circuit of the common IF amplifier not the IF vision detector.
oops, I had not looked back at the schematic and noted this, So Chris, ignore the remark in my post about intercarrier sound. Most USA TV's, even ones older than yours do in fact have it. The idea of it was to avoid any effects of the sound channel going out of tune with drifting of the local oscillator in the tuner. If that drifts the effects are a bit less noticeable for the vision channel as its a wide bandwidth. So on most sets when you adjust the fine tuning knob, you do it for best picture quality, and the sound signal tuning looks after itself.

So in your set, the fine tuning control would be used to peak the amplitude of the sound signal.

In any case, I suggest for now, check all the voltages in the tuner and IF area, the anode voltages of the valves, the AGC voltage, especially as noted the 140V rail. See if you can find anything abnormal. Also check the voltages across the cathode resistor of any of the valves you can as this is an indication of their plate current and if they are biased into conduction, you can compare the cathode voltages on stages with similar valves and similar cathode resistor values even if you don't know what exact voltages should be there.

Last edited by Argus25; 12th Oct 2017 at 10:26 pm.
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