Saturday, May 6, 2017

How to troubleshoot CRT Television with Power supply is dead but voltage at the main capacitor but nothing at the secondary side.

First find out the IC used in the supply and Google its datasheet and find out which pin is V.C.C

This is commonly called start up voltage, if this voltage is absent the I.C not work and therefore the supply will appear dead.

In the example given here the V.C.C pin is 3 and require 18.3 Volts to start. If this V.CC is missing then trace back looking for open resistors (e R802 or R801 and also diode D804 or even PCB broken.

For supply using switching transistor the start-up voltage go the base of this transistor and therefore if you find zero voltage at the base of switching transistor you should again trace back for any open component (usually a resistor in series with the base)

Note: when doing voltage testing here, use the main capacitor negative as your ground.

When you test between the two resistors you should get voltage half the rail depending with your power outlet (I mean 160v for 240vac and 75v for 110vac outlet)

Thank you guys
See you in the next class


  1. Thanks. very clear and informative.

  2. Thankyou.for the good informative read..i surely is helpful

  3. hi humphrey, im jun whats causing a horizontal pink line between the tv screen

  4. some time everything is all right in primary side but no output voltage in secondary side.
    these kind fault many time I see, some time repair or some time not, very confusion type fault this is..So please help to all these kinds type of faults in primary china kits..

  5. Hi sir thanks for the above tips its very useful logics while trouble shooting telivision SMPS

  6. Hi sir,I would appreciate any response from you.I am working on a 21" CRT TV with standby light on but low b+.the start up vcc in voltage is 11v instead of can I diagnose this fault. Cause I traced back and the resistors values are within spec.thanks

  7. Could be a capacitor on B+ line has developed high esr.

    Regards Humphrey

  8. Am working on Panasonic 14inch which had power supply damaged on primary part after changing BBC's and zena diodes I managed to restore 110v 26v and 15v but no 10v on the third diode. How can I trouble shoot this?