Getting Zapped While Isolated From Ground?
This TV (Electrohome/Mitsubishi Model 69CK03, Chassis UM2-C-10R) would power up and immediately blow the fuse on the “cold” side of the circuit board. On the “hot” side (power supply) after changing the bridge rectifier, everything checks normal. I get 125 volts using a 100W light bulb at the (removed) collector of the HV transistor. I changed the flyback. The fuse no longer blows, but the TV goes into shutdown. I removed the CRT circuit board, then pressed the power button and got zapped by the high voltage. No longer taking a chance with my finger on the power button, I used a remote to turn on the TV. There’s a cap between the two 120V line inputs (.01mfd 250V). A piece of plastic surrounds part of the circuit board. When powering up the TV, arcing occurs from one end of the cap to the plastic. I checked the plastic. There’s nothing under it. This is arcing from one of the line inputs. I removed the anode from the TV and measured the high voltage. My meter went up to 40K. I disconnected the TV before it got any higher. No arcing occured with the anode disconnected.
I think that the high voltage is crossing over from the “cold” side to the “hot” side of the board. Or from the anode to the ground straps on the TV tube, to all grounds on the board.
The point is that I have been servicing TV’s for over 20 years. This was the first time I ever got zapped by high voltage by only touching the power button on the circuit board, and touching nothing else. I was also sitting on a wooden chair with my feet off the ground. How many people ever got zapped by pushing a plastic power button? And, as mentioned before, I had checked the power supply for excessive voltage output. I know all the dangers of servicing TV’s, but this was really unexpected, and I wonder to how many people did this ever happen to?
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