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Originally Posted by vts1134
Stupid question, but I'm not afraid to look stupid to get it right. "Hot" and "cold" aren't euphemisms right? If they are not euphemisms then would a simple finger test be recommended for a thermometer (after discharging the HV of course)? How "hot" is hot and how "cold" can it run? Also how long should the set heat up before testing temp?
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Well, assuming it's a half-watt, "hot" would mean blistering and probably smoking after a minute or two. Since it's holding value within tolerance and showing no sign of overheating it would be 'cold'.
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As far as the flyback output is concerned, I will obtain a high voltage probe to measure the output. Does any one know what the voltage should read out of the flyback? Hopefully this will pinpoint the exact problem.
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A HV probe is DC only and will not measure the direct output of the fly, which is pulsed RF. The probe will measure anything 'downstream' of the 1X2 however, which is DC. Since you've already gotten a hefty 'air arc' off the fly and
have seen a raster of full width and adequate brightness, this indicates the fly is performing up to par.
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Tonight I removed, completely, the doorknob from the set. The results with the doorknob removed:
Blue glow on the new 1X2 (although not as strong as when the capacitor is installed). No glow on the old 1X2. After leaving the voltage around 100V for 70 seconds or so both tubes made a pffffssst noise. I fired the set down immediately after hearing this.
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This suggests to me a leakage path from the tube socket itself to ground that's killing the HV and thus leaving resistor R89 cold and unmolested. Is there any way you can temporarily remove the mountings of the socket so it 'floats' free of any connection to ground? This would prove whether or not a leakage path through the mounting(s) exists. The "pffssst" noise certainly sounds like such a leakage condition.
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The only things that are connected post 1X2 at this point are the filament loop, two resistors, and the anode connection on the picture tube. I've tested the set without the anode connection to the picture tube and it failed. Both resistors measure within 20%. The filament loop is solid and double insulated where is loops through the flyback. While the doorknob was removed I took the time to make sure all solder points on the base of the 1X2 are smooth. I'm thinking that the only two things that remain are the 1X2 itself, and the flyback output to the 1X2. I'm going to try another 1X2.
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I would definitely try 'floating' the socket as the next troubleshooting step if it's doable.