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Toshiba CF3566A

Discussion in 'General Electronics Discussion' started by bandit, Jun 5, 2007.

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  1. bandit

    bandit

    16
    0
    May 13, 2007
    I would like to know if the HOT is good or bad on this TV set. I have removed the transistor. It is NOT an original Toshiba part. The last TV repairguy installed a NTE2353 NTP type with a built in damper diode. The part has 3 pins. Anyway, I want to test the part to see if it is good. I am assuming that from left to right the first pin is B. The Second or middle pin is C, and the last pin all the way to the right is E.

    With my DMM on the 2k diode setting I placed the red lead of the DMM to B & the black lead of the DMM to C and got a reading of 499 ohms. Then in reverse I got a zero reading.
    Then I placed the red lead of the DMM to B & the black lead of the DMM to E & got a reading of 38 ohms. Then in reverse I got a reading again of 38 ohms.
    Then I placed the red lead of the DMM to C & the black lead of the DMM to E & got a zero reading. Then in reverse I got a reading of 521 ohms.

    Based on the above assumption of pin locations (from left to right B,C,E) and the recorded DMM Readings (as there can ONLY be 6 combination readings), can anyone please tell me if the Transistor is Good or Bad? If you think it is bad, please tell me why because I would like to learn something in the process.

    I thank you and appreciate any & all replies!!!
    The Bandit
     
    Last edited: Jun 5, 2007
  2. Jimmybravo

    Jimmybravo

    18
    0
    Jul 1, 2011
    Its too hard to tell if that transfer varistor is faulty,unless i test it myself,because i have my own pattern in testing those..the best way you can do is buy a new transfer varistor and compare the too by testing them.. Let me tel you this, a zero reading at any side any pin..b to e,b to c ,etc etc means shorted,and a reading in infinity means its open,but that was using an analog tester,hehe i havent used a digital multi, no budget for that and no idea.hehehe
     
  3. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Just for the record:
    That transistor has an internal (on-chip) resistor in parallel with B-E. It can be anything from 30 to 100 ohms, so the reading of 38 shows the resistor is ok.
    A B-C forward bias of 499mV and a reverse bias of OL (not zero) seems to show the B-C diode to be ok.
    A C-E normal bias of OL (not zero) is good, and a reverse bias reading of 521mV shows the damper diode to be ok. This could be the B-C diode via the resistor though.
    It seems the transistor is ok, but it's not guaranteed since one is unable to measure the actual B-E diode voltage drop with a multimeter diode test - due the resistor.
    To get a definite verification one needs to set up a test circuit, injecting sufficient curent into the base to overcome the resistor current, and measure collector current.
     
  4. sheldonstv

    sheldonstv

    68
    0
    Jul 17, 2007
    ok first checks should be to see if the smps is working....you have already removed the line output transistor....if you locate the ht reservoir cap ,connect a lamp across it(to load the supply)switch on and if the supply is working the lamp will light and you need to measure the ht voltage to see if its in spec(i shall upload the relevant service manual when i find it).sometimes if the supply isnt regulating properly that can cause problems too.
    if thats ok,all other voltages are present,next step is the line output stage.this is where a scope (and isolation tx) is useful so you can check for presence of line drive to the line output transistor....if its present its a case of checking everything in the line output stage for shorts-the lopt is a major suspect here(as well as the transistor you have removed)...
    check for sc diodes,sc caps(or oc caps) and poor soldering(around the lopt,line output transistor,driver tx for the line op transistor,and the frame op ic.)also you need to check the condition of the soldering around the scan coil connector on the board as well....let me know how you get on
     
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