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Grundig Tv Model T-51-540 , power problem

 
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abr
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PostPosted: Fri Jan 25, 2008 9:49 am    Post subject: Grundig Tv Model T-51-540 , power problem Reply with quote

Grundig Tv Model T-51-540 , when i switched it on it's having chik,chik, chik.... sound & the power LED is blinking. The voltage in the Secondary of the Transformer is reading infinite voltage & when i measure voltage in the collector of the Horizontal Transistor ( BU508D ), the voltage is 67v & when i took out the Horizontal Transistor & measure the voltage it's reading normal ( 120 to 123 v), And when i check the tansitsor it's ok. So what could be the problem , help me please
abr
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PostPosted: Wed Jan 30, 2008 7:10 pm    Post subject: Reply with quote

Grundig Tv Model T-51-540 , when i switched it on it's having chik,chik, chik.... sound & the power LED is blinking. The voltage in the Secondary of the Transformer is reading infinite voltage & when i measure voltage in the collector of the Horizontal Transistor ( BU508D ), the voltage is 67v & when i took out the Horizontal Transistor & measure the voltage it's reading normal ( 120 to 123 v), And when i check the tansitsor it's ok. So what could be the problem , help me please
abr
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PostPosted: Sat Feb 02, 2008 6:06 pm    Post subject: Reply with quote

Grundig Tv Model T-51-540 , when i switched it on it's having chik,chik, chik.... sound & the power LED is blinking. The voltage in the Secondary of the Transformer is reading infinite voltage & when i measure voltage in the collector of the Horizontal Transistor ( BU508D ), the voltage is 67v & when i took out the Horizontal Transistor & measure the voltage it's reading normal ( 120 to 123 v), And when i check the tansitsor it's ok. So what could be the problem , help me please
abr
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Mon Feb 04, 2008 10:19 am    Post subject: Reply with quote

Try replacing the BU508D anyway, in some cases those transistors do not fail as completely short circuit, but they might act as a proper transistor in parallel with a zener diode of 50-200 V.

Also, check very carefully that the transistor gets correct base drive and that the flyback caps, any E/W correction diodes etc are in order. Make sure that there are no dry solder joints, suspect electrolytics etc in the horizontal output area.
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PostPosted: Sat Feb 09, 2008 8:17 pm    Post subject: Reply with quote

I came to check that the power on the BU508D is intermittently reading 90 then 85 then 68 then 75 & the same repeatedly , so what might be the problem on ?
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Mon Feb 11, 2008 12:27 pm    Post subject: Reply with quote

It is probably due to the fact that the power supply repeatedly shuts down due to overcurrent and then restarts.

But you should NEVER try to measure the voltage on the collector of the horizontal output transistor of a tv or monitor with an ordinary multimeter, as the flyback pulses might be in the order of 1200-1400 V peak (typically, ten times the supply voltage to the horizontal output), which will immediately blow most multimeters.
Instead, measure the supply voltage to the horizontal output, check out the schematic for the tv to find a suitable test point.
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PostPosted: Mon Feb 11, 2008 2:01 pm    Post subject: Reply with quote

so how am i going to find the schematic of the Tv. & also plz give me some guides to test the Tv . ( the most propablr faults for that )
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Mon Feb 11, 2008 2:31 pm    Post subject: Reply with quote

Probably, you can find the schematic in the database here at eserviceinfo.com . But it is easier to find it if you know the tv's chassis number. Usually you can find it in fine print somewhere on the type plate. Grundig's chassis numbers usually consist of the letters CUC followed by a number of three to four digits.

Make the checks i suggested on Feb 04, this is a good beginning in the troubleshooting. Also, have several BU508D's available.
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