MY SERVICE EXPERIENCES
Part-2
As secondary voltage has been found more than normal, I concluded that this mighe be the cause for the failure of horizontal output transistor continously. Determined to check the voltage to set correct, before feeding it to horizontal output section. So the loaded a filament type 100W bulb after Line Output Supply has been disconnected, as there must be a load to SMPS, otherwise the measured voltages will be improper.
Checked all the solder terminals of components on the power supply SMPS circuit for any loose solder or dry solder. All found to be OK. But I determined to resolder all the terminals of components in the power supply regulator section, especially to some components including the power switching STR, and other resistors. Have done. Switched ON the set. There is no improvement. Voltage measures as it was early 146.5VDC now.
STR suspected. But before replacing the STR, I've replaced all the small elelctrolytic capacitors at the control circuit to the STR as a precaution. And switched On the set. Measured the voltage again. The bulb loaded showed a dimmed light. Alas! It was OK. Exactly 134.89 VDC. The correct voltage. One or two electrolytic capacitors at the power regulator section might cause this problem. Electrolytic capacitors can degrade in capacity with time. That might have happened here.
Replaced the horizontal output transistor, with a new one. Reconnected the LOT supply line. removed the loaded bulb from circuit. Switched ON the set. Secondary power switched ON. OK. LOT began to work filament of CRT ignited. Raster began to appear, but there is something worng again I felt. Connected to external antenna. Selected channel [11] as there is a good on air signal in our area with this channel. Picture appeard, but as the party said me earlier, it was stretched horizontally [expanded], and a 'Sweeking" sound heard from somewhere from the Horizontal output side. Switched the SET OFF at once. Disconnected the Power plug from the wall socket. Touched the heatsink of the horizontal output transistor. The heat to it was abnormal. Unable to touch the heasink. Something short must have there in horizontal output stage. To suspect, components are more. But how to locate the exact one? Let me go on. Will come back to you soon.
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