Too Much High Voltage, Flyback Problem? -'92 Samsung

[RevennaFox]

I'm working on an old Samsung 19" TV, circa 1992. Model TC9865, chassis K50UC. I've cleaned everything up and replaced most of the electrolytic capacitors, but I'm still not having any luck getting it to stay powered on. When powering on, I hear the relay click on, the tube filament starts to glow, and I start to get a raster but everything shuts down after about 2 or 3 seconds and won't power up again without being unplugged for a few minutes. This is what it was doing before I replaced the caps. I think this symptom is caused by the fail safe circuit detecting excessively high voltages and shutting down the set to prevent damage/overheating.

The first thing I do is start checking voltages. On power up the anode voltage rises to 35kV or so before the fail safe trips and it slowly drops back to zero. Normal operating voltage is supposed to be 27kV. Yikes. At this point I turn my attention to the power supply. According to the schematic I should be seeing 150V at the input of B+ voltage regulator Q801, where I'm actually reading about 170V, and 160V on the output where I should be seeing 125. Cause for concern, but nothing apocalyptic. I checked all of the resistors upstream from Q801: R802, R804, R805, R806, and R807 and everything is within 5%. Diode D802 checks out as well.

Nothing interesting so far. Out of curiosity I try to measure the voltage at the HOT collector, at power-on I get out of range on my 600V voltmeter, and nothing on my high voltage tester, so it's between 600V and a few kV. When the fail-safe kicks in, it drops to 165V. I power the set up without the yoke connected and everything stays powered on, with a bright white out-of-focus dot in the center of the screen. Anode voltage at this point is 20kV. Thinking that one of the deflection coils might be shorted, I measure their resistance, 16Ω for the V coil and 2.2Ω for the H coil, which is perfect.

Something must be wrong with the deflection circuitry. I rig up a test and connect just the V coil, I get full vertical deflection and the set stays powered on with a nice bright line down the middle of the screen. Anode voltage is 20kV, and everything is still blurry. I power up the set with just the H coil connected and the set behaves as before, fail safe kicks in after 2-3 seconds as anode voltage reaches 35kV.

Now I know something is wrong with the horizontal deflection front end. I power the set back up with just the V coil connected while I think about it and get ready to measure some voltages and waveforms. I adjust the focus pot on the flyback to try and get visible scan lines and the fail safe kicks in again. I wait for it to reset and power back up and the fail safe kicks it off instantly this time. Reset again and it does the same thing, move the focus pot back to where it was and still nothing.

It looks like the flyback is the problem. I desolder it and read the resistance of the primary and secondary windings. Actual values followed by specified values in parentheses: pins 2-3: 0.3Ω(0.33), pins 3-6: 0Ω(0.27), pins 6-1 0.2Ω(0.42), pins 1-4: 0Ω(0.23), pins 10-5: 1Ω(1.1), pins 5-7: 0.2Ω(0.48), pins 7-9: 0.3Ω(0.24). I don't have much experience with flybacks so I don't know how far off these values can be, but it looks like some windings have internal shorts, although I'm taking this with a grain of salt because I can't find my good multimeter and am using a spare.

This flyback (FCM-2015) is pretty generic part, and I can get one for a few bucks, but how can I be sure it's the problem? More importantly, how can I be sure it's the only problem and not just a symptom? It would be foolish to replace it and have the new one instantly destroyed by a problem elsewhere in the circuit. Is there anything, like for example a bad HOT or voltage regulator, that could instantly destroy a new flyback, or would the protection circuitry take care of it? Or maybe I'm barking up the wrong tree altogether? Any ideas would be welcome.

Service manual/schematic is attached. I also have the factory manual, but it's not as easy to read as the Sams' diagrams.