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samsung le40r51b inverter fault?

 
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taloola



Joined: 16 Oct 2008
Posts: 3
Location: london,uk

PostPosted: Thu Oct 16, 2008 10:49 pm    Post subject: samsung le40r51b inverter fault? Reply with quote

am trying to test an inverter on a samsung le40r51b and i am getting strange results,the drawing below is the connections on the 2 identical inverter boards and there values.when i switch on i get 24v on 1-5, eth on 6-10, nothing on 11, 4.7v on 12, 2.7v on 13 and 3.3v on 14 and the backlight switchs on.after about 8 secs the backlight turns off but the voltages all stay the same as before.i have little experience of inverters but would have expected the on/off voltage to change when the light goes off.
there are 40 transformers and when i test i get continuity accross terminals 1-5 but open circuit across terminals 6&7 on all 40 transformers (2 transformers per tube)(my meter is working ok)

anyone have any ideas or info on testing, am i testing correctly
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Fri Oct 17, 2008 5:18 am    Post subject: Reply with quote

Not familiar with the specific set but you are looking at it correctly provided there are no other external connections. (Also make sure to monitor the same pins before the light goes off to rule out a quick change/recovery)Therefore, based on your readings, trouble has to be within the inverter pcb or may be the FL lamp?(unlikely)
As far as the txformers, chances of all 40 being bad is next to impossible.
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PostPosted: Fri Oct 17, 2008 12:38 pm    Post subject: Reply with quote

thanks for your reply,when the tv is on standby there are no voltages on any of the pins 1-14,when the tv is turned on the voltages are as stated before,then the backlight goes off but the voltages remain the same,i cant understand what is turning the inverter off if the input voltages all remain the same,any help appreciated.
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minnie-me



Joined: 15 Oct 2008
Posts: 17
Location: Mississauga

PostPosted: Fri Oct 17, 2008 3:38 pm    Post subject: backlight/inverter Reply with quote

I have a similar problem with a different model, Benq 26 inch. See my posting a few days ago. I emailed Benq but no reply yet. Mine stays on for about a minute. How long does yours stay on?
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Fri Oct 17, 2008 5:12 pm    Post subject: Reply with quote

Anonymous wrote:
thanks for your reply,when the tv is on standby there are no voltages on any of the pins 1-14,when the tv is turned on the voltages are as stated before,then the backlight goes off but the voltages remain the same,i cant understand what is turning the inverter off if the input voltages all remain the same,any help appreciated.


The inverter is pretty much self sustaining as long as it sees the basic external signals(ie raw supply, protect, on/off/control). It is obvious that inverter is turning off on it's own because of some internal fault. Chances of finding the problem within the circuit is usually time consuming &/or uneconomical. There are many variables involved & even for the experienced often difficult to locate individual parts as it was not meant to be repaired.
For this reason, few if any will provide schematics but if you are interested, suggest getting familiar with the circuitry first. There must be tons of useful info. on the net. Majority of the inverter problems are Mosfets or driver circuits but there is always other possibilities. In your case it could be anything from cold solder, dried up capacitor(s) or a thermal semiconductor.
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