DAMAGED D2499_Horizontal Output Transistor _ SAMSUNG CZ21V5MJ - Deflection Yoke Fault.
The set received for repair, in dead condition. As per information from party, they haven’t used it for a long time; at about 2 years or so; as there was nobody at home. Might be; because, the set too looks so. Whatever it may be; let me work with it.
I did plug the set to AC power and switched it ON. Dead indeed. But, the green power LED at the front panel of the TV lights up for a moment, and goes OFF. That was all. No symptom of software loading or any static EHT effect at the front of the screen.
As the power/standby LED lights up; at least for a moment, means the SMPS section circuit is working normally.
These sets have short circuit protection. If a direct short circuit occurs at any stage at its main board, the SMPS circuit will shut down automatically. That is what happening here. There should be a short circuited component/s anywhere at the circuit board. Where might it be?
The set gives me no time to measure any voltage points. It shuts down, as soon as I switched it ON.
Disconnected the set from AC mains. A meter test done to all suspected components. Detected a damage with the Horizontal Output transistor. Collector to Emitter leak [Direct shorted junction].
If this transistor (D2499) should get damaged, there are 4 possible causes.
* 3k9pF [2000VDC] capacitor. [Free-wheeling capacitor]
* Horizontal oscillator frequency.
* Shorted winding inside the LOT
* Shorted winding in the deflection yoke.
* The 3k9pF capacitor [connected to the collector terminal of the horizontal output transistor to Ground]. Either it might open or the solder terminal loose contact. Checked it. No loose contact. The capacitor showed a value of 4k2pF, with capacitance meter test. It's OK.
* Frequency of horizontal oscillation. If this frequency go beyond a specific value, say if it changes very low or high; the horizontal output transistor will get damaged. The normal frequency is 15.625kHz. about +/- 2% deviation can be tolerated. Not too much.
When the set receive a transmission, this frequency will get synchronized with the incoming RF signal, as synchronizing pulses is being send by the TV transmitter along with video information; to synchronize the picture at the TV end. There are both horizontal & vertical sync: pulses are present along with the transmitting video signal. At the TV end; the synchronization separator circuit; built within an IC, will separate these signals and will routed to horizontal and vertical oscillator section circuits of the TV set; to lock the picture rock-rigid.
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Here my problem is how I can measure this frequency.
If I could measure it; the set should switch ON; and stay ON.
Here the set switches ON and shuts OFF due to the shorted horizontal output junction. If I rectify this short-circuit, the set will stay switched ON and I can measure all other voltages.
I de-soldered out the horizontal output transistor from circuit board. Switched ON the set, without horizontal output transistor.
Now I can and did measure the DC [+B] supply voltage with volt-meter. This 110VDC supply voltage was OK.
Plugged the set to AC, and switched it ON.
The power/standby LED now stay ON, just for 5 seconds and shuts OFF; indicating a software load up.
Measured the horizontal frequency at the base foil point of the horizontal output transistor. Found OK. 15.596kHz.
Switched OFF the set. Soldered a new horizontal output transistor of same number in place. [D2499]
Plugged to AC power, and switched ON.
An EHT static felt at the front of the screen; but, within 10 seconds the transistor became very hot.
Either LOT or the deflection Yoke might be the reason.
Disconnected the deflection yoke plug from the main board.
Pulled out the CRT base card from the CRT neck and kept it securely without making any short circuit to it with any other components on board.
Switched ON the set, after plugging it to AC mains.
Checked the heat of the horizontal output transistor after 5 seconds. It was normal.
Means, the deflection yoke have the fault. If the fault was within the LOT, the transistor might have heat up this time too. It is difficult to detect the winding short, either to LOT or deflection yoke. The only way is to check it by replacing with an other good one of same number.
I too did it.
Switched ON the set. OK.
On checking, the deflection yoke the winding of it have corroded. Might have short inside in between adjacent turns. That was the fault.