Thursday, March 8, 2012

Customer support-email between me and Mr Romeo from Philippines

Hi Humphrey,
Thanks again for your guidance. Now the Toshiba TV is fine now 
when I did what you've suggested.

Great! Congratulations Romeo

 Now we go back to other TV unit which I consulted to you earlier. That one which I heard tweet, tweet sound when it is powered on. In that condition no voltage in the secondary side especially from the secondary diode that supplies power to the B+ line. You suggested that I disconnect the B+ line from the flyback transformer which I did then the tweet,tweet sound stopped.

Okay… Noted

This time I checked the voltage from the B+ line and got 102 volts (B+ line disconnected from flyback) but unstable, this voltage supposed to be 110Volts as shown from the schematic diagram.

This presence of the B+ concludes that the primary power supply is working well and should not be considered for further troubleshooting. Again with the flyback out of the circuit the 102 Volts is ok. Let’s move on.

When I checked this voltage with analog multimeter the needle is shaking which shows unstable reading. But when the B+ line is connected there is no voltage shown in the multimeter.

Usually for Voltage testing use the digital meter, so far I don’t suspect any serious issue here since you already have 102 volts on this line.

There is voltage from the filter cap which is 310(220 volt power source).The IC driver (L6565) which is 8 pin has 11volt from the Vcc pin. There is also a N-channel MOSFET in the primary side. I checked this component out-board with analog multimeter and it is ok too. There is also voltage reading in the DRAIN pin which is the same as in filter cap, but no reading from the other two legs.

Since we have the output on the secondary side, this means the primary supply is working well.

So upon seeing all these results my question is one, why there is voltage in the secondary diode when B+ line is cut off from the flyback.

This means the primary supply is okay and we should concentrate our effort on components after the takeoff..This include the flyback itself, the HOT is shorted, the horizontal yoke shorted or Short or excessive load on secondary supplies fed from flyback.

To isolate this problem Romeo do this… 

    1.Solder back the B+ line, remove the yoke and power On..Still tweet, tweet sound? It still there this mean the yoke is okay. Power off and return the yoke to the connector. 

    2.Lift up the middle leg of the H.O.T transistor and power up? Tweet, tweet gone? If yes then it means the H.O.T is shorted or components on the secondary side of the flyback transformer. If the tweet, tweet continues after you remove the middle leg of the H.O.T then we can conclude that the flyback is faulty and should be replaced.

Two, why is the voltage unstable, is there a defective component somewhere in the primary side or secondary side?

So far I don’t suspect the primary side Romeo.

Is the flyback is main culprit?If so pls.give me some hint in disconnecting the flyback transformer.

I would say yes and No, use the above method to isolate the real culprit but still the flyback is highly suspect.

To remove the fly back transformer from the circuit you need higher wattage Iron gun and solder sucker (this one is a must) and be sure you suck the solder on all the fly back pins. 

Then using a big flat screwdriver try to push between the fly back body and the circuit board and rotate the screw driver slowly and carefully until the fly back come out.

Please don’t use force otherwise you are going to break the board, if you find still the fly back is not coming out easily this could mean there is still a strong joint and should be checked and solder it out.

Is there any means of testing flyback out-board other than flyback tester? Sir I cannot settle all these things without your technical guidance, so pls. I want to read your soonest reply.
Regards, Romeo

Yes but the best test is by substitution

All the best Romeo Humphrey


  1. I like this concept. I visited your blog for the first time and became your fan. Keep posting as I am going to read it everyday.

    1. Keep coming, for that cause we are here.
      regards Humphrey