Quote:
Originally Posted by RevennaFox
.... and 160V on the output where I should be seeing 125. Cause for concern, but nothing apocalyptic.
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Yes it is!
That is your problem right there. This TV uses the LV regulator as the HV regulator. The HV is proportional to the LV, so anything more than 125VDC and the HV runs away proportionally.
You've got one of two problems: either C457 is open (47/150) or your Q801 (STR30125) is shorted internally.
Change the cap, if that doesn't fix it, look for the STR if you can find one.
If you want to troubleshoot this a bit for fun, unsolder the Horiz output transistor and remove it from the TV. Put a 75W incandescent bulb wired from the Emitter to the Collector points of the horiz output and turn the TV on. The bulb will light - measure the voltage across the bulb.
If the voltage is 125VDC at 120VAC input, then your C457 is open. If the voltage remains at 160, then the STR is bad.
The STR series of self contained series/pass regulators were made by Sanken and are generally reliable, but they do fail. They contain three or four transistors, some resistors, and a zener or two. These are fixed regulators and the part number identifies what the output voltage should be. So if you STR is a 30125, then you should get 125V +/- 1v over the full range of bright to dark scenes. You can put a STR30120 in place of it, but your B+ will now be 120V and your HV a bit lower as well. If that's all you can find, you may have to fudge the retrace cap on the horiz output to get your HV back up. Do not use a STR30130, 135, etc as the HV will be higher. It may not shut down but you'll be stressing the flyback and pushing the CRT filaments beyond 6.3 as well.
John