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Panasonic rear projection tv

Discussion in 'Troubleshooting and Repair' started by theshftmn, Dec 14, 2010.

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  1. theshftmn


    Dec 13, 2010
    Hi all, new to this forum I am working on a Panasonic rear projection tv PT45LC12. The set blew the bulb and a replacement was purchased from a Panasonic dealer. The set lasted about a week and no bulb light. The set powers on and blinks green then red then shuts down. According to the manual either the bulb is bad or the ballst is bad. I have replaced all the components in the ballast with the exception of the transistors (4) only 1 included in the kit. I have tried to test the transistors (K2842) out of circuit. The test was 1. Ensure the MOSFET is out of circuit, then place the DVM into the Diode test position. Attach the positive lead (Red) to the Drain terminal, and the negative lead (Black) to the Source terminal. Confirm an Open circuit condition.

    2. Leaving the negative lead (Black) attached to the Source Terminal, remove the positive lead (Red) and briefly attach it to the Gate terminal. This applies a voltage to the gate of the MOSFET through the DVM's internal battery.

    3. Repeat Step 1. This time, confirm device conduction.

    4. Attach the negative lead (Black) to the Gate Terminal, and the positive lead (Red) to the Source terminal. This turns the device off by reversing the Gating voltage (making it more negative). Repeat Step 1, and confirm an Open circuit condition.

    the test failed number 4, I am assuming that the transistors are bad. I applolgise for the long post, trying to give enough information, I have also checked the thermistor for the lamp

    Any help would be appreciated, thank you in advance
  2. Resqueline


    Jul 31, 2009
    It's very strange that it would pass step 1 (open circuit) first, and then fail step 1 (after step 4). Try to just short the gate instead while in step 3, it should do the same trick.
  3. theshftmn


    Dec 13, 2010

    Thank you for your help, I found 2 of them bad.I am going to replace them all. Will let you know how it goes.
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