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Re: Horizontal Output Transistor
This philips board give many problems with no raster. Most times its Horizontal and sometimes it transformers I have found it would be much simple to buy board or send off to be repaired. Pts 1800-844-7871 is the best bet. You also can get hot at places like MCMelectronics, bluestar international, tritronics. If you do not want to buy board.
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Check its horizontal output stage circuit for any short. Check the horizontal output transistor, for collector to emitter, of collector to base, leak. Replace it with a new one and check whether the newly replaced transistor gets too hot. If so, suspect the FBT. To get some details, http://electronicshelponline.blogspot.com/ Pull up older posts.
Hello You are talking about the horizontal output transistor damage I assumes and post this solution. If LOT has internal winding short, the horizontal output transistor will get shorted. It will be best to replace the horizontal output transistor, alongwith the LOT
Six blinks denotes the absense of horizontal sweep. Check the horizontal output transistor, whcih can be located very near to the LOT [Line Output Transformer]; for short. If it is shorted, LOT must be suspected. Replace the line output transistor with a new one, and switch ON the tv for a short period of time, say 6 seconds or so, and check the heat of the replaced transistor. If it overheats within this time, be sure that LOT is damaged; shorted inside; and should be replaced with same type and number. If a digital multimeter which can measure frequency is available, take the frequency at the collector of the horizontal driver transistor. It should come around 15525Hz. If not replace the jungle IC. OK.
Before replacing an other one, replace the freewheeling capacitor, the capcitor fitted between the collector of the 2222 and earth; usually of a value of 3500pf 2000VDC, some times this value may differ from set to set. If this capacitor has opened of developed in value, the result will be the failure of the horizontal output transistor, at switch ON itself. The second reason is the short in horizontal yoke windings. Even one winding get shorted, it will cause to a heavy load flyback transormer which in turn to 2222 failure. The last reason for this fault is defective Line Output Transformer itsef. Check these three.
Before proceeding, desolder out the horizontal output transistor 2222 fro circuit, and measure the frequency at the collector point of horizontal driver transistor. It should be around 15625HZ [may differ a little], with no signal. If this frequency is found higher than normal, The main IC jungle should be suspected.
Anyway, go forward after checking this frequency. OK.
The F27442 uses the CTC203 series chassis and that symptom is very common. If the horizontal output is shorted you MUST resolder the coil in series with the base of that transistor and the pins of the small horizontal drive transformer. When they have been properly resoldered you can put in a new original horizontal output transistor. If the output transistor shorts out again then your flyback (high voltage) transformer is shorted and needs to be replaced.
The horizontal output transitor is always connected to the primary winding of the flyback transformer (via collector) and also to the horizontal deflection coil via an electrolytic capacitor.
The most likely suspect for damaging the transistor is the fylback transformer. In some countries there are electronic stores that test flyback transformer by winding a few turns on the ferrite core and applying a test voltage. This test will only test the secondary.
The primary winding is difficult to test for turn to turn short because the resistance is quite low and you do not know the 'good' resistance.
Check for shorted base-collector junction on horizontal output transistor designator Q14401. Also coil L14401 going to base of transistor needs to be desoldered, scrape ends, resoldered. If horizontal transistor is shorted, real possible flyback transformer bad.