Pages

▼

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


at

11 comments:

  1. RPRAVMay 10, 2017 at 12:03 AM

    Thanks. very clear and informative.

    ReplyDelete
  2. mustabzMay 10, 2017 at 11:13 AM

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

    ReplyDelete
  3. UnknownMay 18, 2017 at 9:58 AM

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

    ReplyDelete
  4. pankaj sharmaMay 27, 2017 at 10:49 AM

    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 side..in china kits..

    ReplyDelete
  5. pankaj sharmaMay 31, 2017 at 12:12 PM

    Thanks Sir

    ReplyDelete
  6. basavaJune 24, 2017 at 5:58 PM

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

    ReplyDelete
  7. Efije PhilipOctober 14, 2021 at 2:28 AM

    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 19v.how can I diagnose this fault. Cause I traced back and the resistors values are within spec.thanks

    ReplyDelete
  8. Humphrey MndakaOctober 15, 2021 at 11:00 AM

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

    Regards Humphrey

    ReplyDelete
  9. Fets repairMarch 2, 2024 at 9:35 PM

    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?

    ReplyDelete