Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/off

[lucasius]

My Samsung LCD TV (LN40A550-P3F-XZC) stopped working :-( I hope someone can help? Symptoms: the red standby light blinks all the time, and the white light at the bottom-center of the screen is on, but there is absolutely no image (not even in a pitch dark room) and also no sound. The voltage on the STB 5.3 pin measures 5.1V and the voltage on the PWR On/Off pin measures 4.33V. The strange thing is that I can't turn the TV off either: as soon as I just merely connect the power cord, the situation will become as described above: white light at the bottom-center of the screen is on, red standby light blinks -- can't turn it off, not with the remote control nor with the on-off button on the right side of the TV: white light at the bottom-center of the screen stays on, red standby light keeps blinking. The only way to turn off the TV is by disconnecting the power cord. However, interestingly, when I keep the TV unplugged for a few weeks and then plug it back in after all that time, then the TV may work as normal for a couple of minutes, showing a perfectly fine image from a local TV channel when I turn on the TV via remote control or on/off button, but then suddenly the image freezes (showing at much lower resolution and also colors off, sometimes accompanied by a loud buzz coming from the speakers) and then the next thing is screen goes black, no sound. FYI: I'm using a properly grounded power outlet (no surge protector in between). I'm trying to figure out which board in the TV might need replacement (I can check Ebay if they sell the board) -- I suspect it must be either the *PSU board* or the *main logic/video board*. Just want to avoid buying one of these two boards and then the next thing is it turns out that the board it replaces wasn't the one with the defect after all. Thanks in advance for any help/hints from anyone! B.t.w., although the caps on the PSU board are all looking good (no bulging/leaking), I replaced them (Rubycons from DigiKey) -- but it didn’t fix the problem. Maybe another component on the PSU board could be faulty (maybe a voltage regulator)? Or would the main board be the more likely suspect now?

[DakotaKid]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

**thanks**

[lucasius]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

I did some voltage measurements on the pins and found:

* pin Power On/Of pin = 4.2V -- interpretation: power board powered on, also explains white light at the bottom-center of the screen is on; merely connecting main power cable gets TV in this state, can't power off (to get pin voltage near 0) using power button, power off commands seem to simply be ignored
* pin Inverter On/Off = 0.03V -- interpretation: main board not sending inverter-on signal to power board, hence no backlight seen; backlight comes on when I manually apply 4V to this pin
* pin Sync (pin 2) = fluctuating voltage -- changing in time anywhere between 0.3V and 4.3V, values seem random, not sure what to think of this, anyone has any suggestions?
* All other pins showing expected voltage values

Starting to think that my main board may be fried? Or maybe the EEPROM reset/replacement trick could work to fix the problem? Anyone has any thoughts?

[ron77]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

From the voltage readings you have taken, and the way your tv is performing, I would suspect the main board. I am only going on my own experience,after working on a number of Samsung tv's over the last six years. However, I can only remember one model of samsung tv that had a chronic problem with the main board. That was the Le40r88bd. This was caused by two capacitors, sometimes more, swelling on psu. Poor standby voltage caused main eprom to fail. In fact it got very hot.This tv had relays that kept clicking, I suspect your tv has no relays. Anyway models before this one, and after, caps going, main board survived. No invertor on voltage on any of those faulty boards.Bar capacitors failing had few problems with Samsung lcd psu's. Repaired a celcus tv last week, a vestel tv.Had voltage readings identical to yours, was main board faulty. If it is the main board playing up, I change them, pulled ones are inexpensive.

Ron77

[whatusername]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

Hey guys i just got the same tv same issue blinking red light..If i left the tv alone for a long time it would attempt to turn on. you can hear the samsung chime then see backlight and when you look at the screen its flashing like low on power then shut off.. i found 1 bad cap on power board replaced it and still same thing blinking led.. but this time after a while it attempted to start again i heard half chime and then a annoying squeal coming from the speakers.. i did check all voltages on power board and everything is correct... the optical out on main board is not lit up but then when it goes to power on it lights up thats how i know its gonna attempt to start from behind.. i would like to fix this board if possible so where should i start?

[whatusername]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

bump

[whatusername]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

no one wants to help take on this challenge? i hear it could be the Ic but im not sure

[budm]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

@whatusername, what is the power supply board P/N? BN44-?????

[whatusername]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

get you that info right now bud

[budm]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

One of these?
http://www.shopjimmy.com/catalogsear...lt/?q=LN40A550

[whatusername]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

bn44-00197A

[budm]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

OK, here is the SCH.
So all the voltages (stb5.3V, 5.3V, 13V and the signals (Power_on/off, Inverter_on/off are >2.5VDC). If that is the case, then the problem will be in the main board. I never have luck fixing the Samsuung main board myself.

[whatusername]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

power on 4.32 stb 5.12 13's are 13.00v

[whatusername]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

inv on off 0.03

[budm]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

OK, what you can do then is to disconnect the INV ON/OFF wire going back to the main board first and then use 100~1K resistor between INV ON/OFF and the STB5V to force on the backlights, we have to disconnect that wire because we do not want the main board to keep forcing the inv on/off LO and not allow it to go HIGH when we try to force the line HIGH. When the bcaklights are on, if everything else is OK on the main board then you should see the pictures, and hear the sound and all the function should work.

[whatusername]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

cn803: connected to main
det 5v= 5.11
gnd=0
pwr dim= 4.76
nc= 2.46
inv pwr on/off = 0.03
if removed from main nc=0

[whatusername]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

i dont have a 100 -1k resistor i dont have any resistors.. i do have a light bulb.. i remember we used it once just cannot remember how

[budm]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

You can do without the resistor, the reason we use the resistor is just in case you slip and touch something else, the resistor will limit the current.

[whatusername]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

ok jumped it and bl came on front led still blinking red not responding to button presses

[whatusername]

Re: Samsung LCD TV: no picture/sound, red light blinks, white light on, ignores on/of

wait u said use 5v stb? i used det 5v does that make a difference?