Friday, January 21, 2011

PANASONIC TV MODEL TC-14E1T with intermittent single horizontal line (blue), sometimes screen is lit but no picture, sound ok. Also the osd(ie channel number is visible but blurred)




Panasonic Television with intermittent single horizontal line

Intermittent problems are mostly caused by dry joints; you can confirm this by hitting the Television gently with bare hand on the sides. This I did and confirmed there were many dry joint because the screen kept on changing.


Sometimes I even managed to get a picture, which was reddish purple in color. I mean this Television has all sort of weird symptoms.

The Television was using I.C LA7837 for the vertical Drive so I decided to Google for the datasheet of this IC and I bumped on this shown in the diagram below.



You know sometimes if you fail to get the circuit diagram of the exact model you are working on you can go round this problem by getting only the data sheet of the suspect I.C and this can go a long way in assisting you to know which pin is which for proper diagnosis.

Very important is the supply (v cc pin) which is very important because a new working I.C from the factory is as good as a bad one if the V CC supply is missing, it’s like trying to drive a new car without gasoline.

That is why it is very important to make sure the supply voltage to any I.C is present and is correct value. So from the data sheet I was able to see that for this particular I.C LA7837 it is feed by three Voltage sources.

Pin 1 is feed with 12 Volt DC; pin 8 and 13 is feed with 24 volts each, Please note that the 12 volts is from the secondary of the power supply and the 24 Volts is from the secondary of the fly back transformer and therefore one can fail and the other remain but still the vertical I.C will not work.

I mean if any of the three supplies is missing the vertical I.C will not work and therefore if you find any of the supply missing be sure to do the voltage testing from that pin backward and find out what is blocking the voltage.

Look for open fusible resistor or filter capacitor for that line has developed high ESR. Usually if capacitor has high ESR causes the supply for that line to drop.

One thing I was sure about is that there was a problem with the vertical circuit. I measured all the components around the vertical I.C and they seem okay according to my meter.

The voltages were also okay to me. I.e. main supply 24volts both sides of the diode, and 12 volts for pin 1.

After doing a lot of re-soldering on all the suspect areas including the main ic which generate the vertical pulses i finally decided to change the vertical ic.

This made the Television come back to life.

Below see the actual vertical circuit of this Panasonic Television



Conclusion:

1. Intermittent horizontal line in crt television and monitor is usually caused by dry joint on the Vertical IC or dry joints on the vertical yoke connector
2. Capacitor dried up…try touching the top of electrolytic capacitors around the vertical ic and whichever is getting hot should be replaced.



If all the supply voltage to the vertical ic are okay and still you are experiencing vertical failure symptoms consider replacing the vertical I.C directly.




Thank you guys

Let meet in our next class.

Wednesday, January 19, 2011

How to fix an Onkyo receiver

If you want to fix your own Onkyo Receiver...Click on this video recommended by Mr Beh.

Wednesday, January 12, 2011

Understanding the Degaussing coil in CRT television


Understanding the Degaussing coil in CRT television


CRT Television and monitor are affected by the Earth magnetic field and for this reason Engineers designed the degaussing coil in order to take care of this effect which is usually manifested by colored spots on the screen.

Besides the magnetic field caused by the earth there are also other causes like placing strong magnet near the CRT television and therefore it is advisable to keep Speakers away from the set, usually when you find a television has spots on the screen first be sure there is no speaker or big radio(speaker inside) near the set.


One cannot talk about the degaussing coil without mentioning the Posistor(PTC). This is because since degaussing coil has very low resistance and is directly connected across the AC power line(240 Vac or 110 Vac) then it would create a short circuit across the power line but this is not so thanks to the Posistor(PTC) which is connected in series with the degaussing coil and when power is switched on the Posistor which has low resistance when cold but very high resistance when hot and therefore the coil will Pass current just for a moments before the Posistor get hot and cut off the current trough the degaussing coil.
 

Effect of the power supply when the Posistor fail:

1. Open - No effect on the power supply, only lose the demagnetizing effect of the degaussing coil (picture with spots)

2. Short - If the posistor shorts it means the coil will create a direct shot to the power supply and therefore fuse will blow.

In conclusion I wish to encourage technicians to take time to check the circuit diagram in order to see how the component is positioned (series or parallel) to the supply because by this one can be able to conclude the effect that component can have if it fails shorted or open.

 Thank you guys

Let meet in the next class








Monday, January 3, 2011

Happy new year everybody

Humtech electronics is back!! but not without a challenge..after proceeding for a short leave i encountered this television Sony KV-BT212P40 made in Malaysia which decided not to listen to me even after several rounds of attempt to wake it up.

i wanna give it another trial but i need your BIG HELP from you dear Techs...IF YOU HAVE THIS circuit diagram PLEASE KEEP IN TOUCH WITH ME...

Otherwise let discuss more in the next class.

Regards Humphrey