Samsung le40a756r1m

[sordids999]

Hi guys bought this tv today was told the screen will go black after a while but still has audio so been running it for a while today but everything seems ok

any ideas ive attached voltages and pictures of the chassis and boards

[wills123]

Re: Samsung le40a756r1m

might of knocked a connection taking it apart, try cleaning and reseating them all

[sordids999]

Re: Samsung le40a756r1m

I've since changed the psu due to having a spare just in case it was that all voltages I thought the 12V was running low at 11.1 but they are still the same with replacement psu, so testing now, could it be the panel ? Well if it goes on me

[tom66]

Re: Samsung le40a756r1m

I've had an LE40A656 which would reboot when the 13V went below 11.5V. (There's a 12V and 13V rail, they are different.) In that case it was bad capacitors. I'd advise replacing them anyway on these models as they have a high failure rate.

[sordids999]

Re: Samsung le40a756r1m

ok thanks m8 ill try change them all

[sordids999]

Re: Samsung le40a756r1m

what caps do you recommend tom ?

[tom66]

Re: Samsung le40a756r1m

You can buy high quality Panasonic FC, FM or FR capacitors from CPC a division of Farnell.
I think I used a mix of FM and Nichicon PW capacitors (because I had them on hand, Nichicon is also high quality like Panasonic.)
That TV is still playing well about 18 months later, gave it to the parents.

[sordids999]

Re: Samsung le40a756r1m

ok just a quick update changed all the caps to Panasonic like tom suggested ok at the moment been running all day,not saying its fixed but hopefully it will be fingers crossed

[tom66]

Re: Samsung le40a756r1m

That's good to hear. Make sure to do a full factory reset after replacing capacitors - corrupted EEPROM can occur due to bad caps causing other/future issues.

[sordids999]

Re: Samsung le40a756r1m

yeah already done that thanks tom

[asesutomas]

Re: Samsung le40a756r1m

my LE40A6561F does the same... after a 4-8 hours of work the TV lamps goes off.... then i plyg the AC out from the wall... wait for 2 minutes and than everything goes ON again... and just one more thing... when TV is ON and i go in MENU>SETTINGS>ENTERTAINMENT and choose something between SPORTS CINEMA GAME OFF... when i go between these options the lamps goes OFF.... even the TV is On just for 10 minutes...

[sordids999]

Re: Samsung le40a756r1m

i changed all the caps and its still runnning it was for a family member only spoke to them the other day the tv still has not cut out

[tom66]

Re: Samsung le40a756r1m

my LE40A6561F does the same... after a 4-8 hours of work the TV lamps goes off.... then i plyg the AC out from the wall... wait for 2 minutes and than everything goes ON again... and just one more thing... when TV is ON and i go in MENU>SETTINGS>ENTERTAINMENT and choose something between SPORTS CINEMA GAME OFF... when i go between these options the lamps goes OFF.... even the TV is On just for 10 minutes...

This is indicative of a problem with the lamps, one is wearing out. You will need to turn the backlight level up and turn off any dynamic contrast mode. It will give you an extra bit of life. In my case it worked for over 2 years but it doesn't always.

[asesutomas]

Re: Samsung le40a756r1m

This is indicative of a problem with the lamps, one is wearing out. You will need to turn the backlight level up and turn off any dynamic contrast mode. It will give you an extra bit of life. In my case it worked for over 2 years but it doesn't always.

realy???
hmm... interesting... i have tried many things with this TV:

1) replaced all electrolythic caps on POWER UNIT BORD... seemed like the problem is solved... but not...

2)than tryed to search the problem in PCB where LX1692BIDW stands...

http://circuits.datasheetdir.com/59/...IDW-pinout.jpg

i thought that problem is in this chipp.... so - it watches the HIGH VOLTAGE lamps – PIN number 14 ISNS - waches how it works and found in CHIPS manual that: ""Current Sense Input. The ISNS input is full wave rectified by an On-Chip circuit, then presented to the inverting
input of the current error amplifier. Frequency range of the input signal is DC to 200KHz. The ISNS pin also
monitors lamp current to determine if the lamp is ignited. If a single cycle at the ISNS pin is greater than 0.7V,
the strike / run flip flop is clocked to the RUN state and threshold of the strike comparator is lowered to 0.3V.
During RUN mode current levels are continuously monitored to detect less than 0.3V. A counter clocked by
RMPD_OUT is reset each time current is sensed at this input. If the counter overflows (256 counts) a fault latch
is set which shuts down the IC. This fault is expected to occur when the lamp is shorted to ground through an
impedance of less than 2K ohms or the ISNSresistor itself is shorted. The counter is inhibited during digital
dimming off time. Normal operating voltage levels will be in the range of ±0.5V to ±5.5V. An abnormal voltage
can operate continuously as high as ±7V peak under load fault conditions. Transients under fault conditions up
to ±11 VPK are permitted. Input voltages up 4V peak are linearly rectified. An input voltage above ±4V peak
but less than ±11V peak may cause saturation but will not cause malfunction, phase reversal, or reliability
issues with the IC. "... so i think it can be something wrong with the HIGH VOLTAGE UNIT... some voltage peaks or something that puts this chipp OFF when it senses something bad.... im confused.... how to solve this problem...


but now i think it can be true - maybe lamps is a little bit messy and the driver shuts down the HIGH VOLTAGE unit... to prevent something

i think i will go and test every single component around this chip: every resistor, capacitor, transistor and diode – maybe something will come out....

and one more thing seems that when TV is cold – just turned on, you can go in MENU>SETTINGS>ENTERTAINMENT> ad select OFF CINEMA, MOVIE, SPORTS jusg go selecting up and down up and down... everything seems ok, but when you run TV a little bit longer (hour or two) THAN when you do the same – it shuts down the laps imediatly....

[asesutomas]

Re: Samsung le40a756r1m

This is indicative of a problem with the lamps, one is wearing out. You will need to turn the backlight level up and turn off any dynamic contrast mode. It will give you an extra bit of life. In my case it worked for over 2 years but it doesn't always.

onemore question TOM, by saying wearing out - you mean - wearing out in place where HIGH voltage board connects to panel or in other side - the sealed one - where all lamps goes together?

here is an pic

http://i1.ytimg.com/vi/uEcQUeg-jLA/maxresdefault.jpg

wearing out in left (from picture wiev) or right side?
and - is there some method to test it - that its true? because when you put the HIGH VOLTAGE unit on the panel, it closes all holes and you cannot tell - that lamps are connected well or not....

[tom66]

Re: Samsung le40a756r1m

No I mean the bulbs themselves which have a limited lifespan are wearing out.

[Dang]

Re: Samsung le40a756r1m

What tom66 is saying is that the CCFLs requires more current/voltage to spark up and stay lit in it's current state, hence turning the back light setting up, if the current/voltage drops below the heightened minimum threshold(due to age), then the CCFL will extinguish, this is why it's best to turn off any dynamic back light settings as the current/voltage will fluctuate to a point where it may become too low for the CCFL to use, this is also why choosing a different picture mode setting will cause the back light to turn off as you have seen, I hope this helps.

[asesutomas]

Re: Samsung le40a756r1m

thank you guy's, your words was useful to me. now it's more clear about this situation.

[asesutomas]

Re: Samsung le40a756r1m

and by the way - i think that get inside the panel and try to change the lamps - is very hard thing, in fact maybe it isn't worth changing?