Tip & How-To about Philips Televison & Video

How to test Flyback Transformer Without taking it off the Board




How to test Flyback Transformer Without taking it off the Board


a) Basically it has to be acted upon by a supply voltage of at least 95V

to work.



sample picture:




b) Of course, assuming the horizontal deflection oscillator works, same

with the horizontal drive and horizontal output transistor



sample of H out transistor




It would generate output voltages on the secondary terminals

and 200V line will be active sending voltages to the

Video Drive circuits. Of course high voltage will be generated

ranging to at least 30 KV and there will be voltages on the G2 of the CRT.


c) The easiest test point to look when it is oscillating, is the CRT heater

voltage, the heater lit when flyback is good ( mostly at night times when it

is dark ) and you can hear sounds, too ( if speaker is connected).









• Heater : marked with letter H and H1

• Green Arrow for the G2 voltage


d) Having a B+ voltage reading of 75 V or lesser ( primary pins )

indicates a bad or partially shorted flyback, assuming your

horizontal output transistor and power supply are good & OK.











• These only applies to CRT type TV's.

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1 Answer

why not flyback oscilate or fly back voice?


I am unable to give any specific advice but if there is voltage or power to the Line Output circuit then its possible a short or load exists on the flyback transformer which causes a shutdown in this circuit.
I am afraid practise and knowledge of a particular model is a great help to find its faults.
The Flyback transformer (if like I remember) will have sub power supplies from it to drive audio, frame etc so a short on these will cause problems, also the rectifier diodes to these can fail you may need to remove one end of a diode for accurate testing.
Another failure point in power supply rails is capacitors which go open circuit this makes their voltage line unstable, also on the capacitor problem list are those around its flyback circuit that act as snubbers to tune it, these were at my time little blue capacitors of several KV which had a habit of shorting or change value.
Any of these will disturb a balanced start up cause a spike and shutdown.
Without particular knowledge of a model and its circuit I am unable to help further, I would look for shorts on Diodes and components, disconnect supply rails to audio and frame if they come from the flyback transformer (these are the heaviest loads and will only serve those particular circuits) then it will possibly capacitors gone o/c (I used to carry a cap tester years ago which used a 555 ic easy and robust).

Hope this helps in some way...

Mar 05, 2015 | LG Televison & Video

1 Answer

flyback KPT6AW4SSF not working losing voltage.


Hello
If there is a voltage drop with flyback transformer connected, keep its supply point desoldered, or make a nice cut on track which supplies the FBT. That is isolate it from the main supply rail and check the voltage again. If the voltage is found normal now, desolder and take out the Flyback Drive Transistor, and check it for any leak, check it for collector to base leak. A good quality analogue multimeter is recomended for this check, beacuse digital multimeters cannot display this correctly. If it has a little leak as specified above, it will overheat after some seconds of working. Anyway replace it with same type and number.
If the fault perists, FBT should be replaced. After its replacement you should retune its focus and screen voltages for proper picture.
Hopes that you can do. Wish you sucess. Ok
If any doubts, inform Fixya. The will send me alerts.

Oct 21, 2010 | Panasonic CT-32SL14 32" TV

1 Answer

hi i m sanjay i m having sony colour television kv-2782me7 i found some problem in power supply section i m geting low voltages frm secondary output i want 135 ,25 ,8 , and -33dc voltages bt i m geting only 50 ,6 ,2 and -10 dc voltages i checked all components in secondary section bt i could nt found any diffective component can u help me plzzzz


there is a possibility of a shorted turn of the flyback transformer. To test. short B-E together on the horizontal output transistor and connect 60W globe across C-E. measure voltage across lamp - if it comes up to 135v then you have a short either in the horizontal circuit or secondary circuit off the flyback transformer or even the transformer itself.

Aug 10, 2010 | Televison & Video

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