Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

[Bertron]

... but the samsung logo in the bottom does light up. 5.13V standby power holds steady even through the 'clicking'. The huge capacitors in the middle of the IP board give me 392 and 393V. I have replaced all of the capacitors except the two huge ones with no changes in behavior. I even tried resetting the EEPROM (or what I thought was the EEPROM, there is no IC with 'EEPROM' explicitly marked on it) with no success, by soldering wire to pins 5 and 6, holding them for two seconds then letting go. I am mentally drained from getting nowhere with this thing and would really appreciate any pointers and suggestions as I am still a rookie at this. I will post pics tomorrow morning if they help. Thanks a million.

EDIT: forgot to mention all the fuses in the power board are fine

[attainteddragon]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

since you have 393v on the main cap, that would mean that your main board is sending the ps on signal to the ps which in turn is activating your pfc section.

now you need to check the connector that leads to your main board.
dcv, black probe to chassis ground.
pin label, stby voltage, on voltage.




working blind till you get those pics up!

[Bertron]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

http://imgur.com/a/ZAuQX

uploaded the pictures to IMGUR as part of an album for this repair

I took the voltage readings for that whole connector. The readings are as follows:

DESIGNATION.................READING
13.0Vm.........................13.15V
13.0Vm.........................13.15V
13.0Vs..........................13.57V
STB5.1V........................5.16V
Sync.............................3.192V
PSON............................14.09V



should STBS 1V read.... 1V? I am getting 5.16V there....


thanks for the help, I am poking around a lot of the test points theyve built onto the board, but without proper schematics its really hard to get anything done.


EDIT: 'STBS 1V' was really STB 5.1V... I am a dummy. Thanks for clearing that up andrew

[Andrew F. Ali]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

I think what you read as STBS 1V......is really STB5 .1....Which is OK....You may have a T-CON Bd problem or Inverter/Driver problem to power the Backlights....I couldn't view your picture/s from the link....But look for BL-ON on the same or other jack on the PSU and see if it is >2.5Vdc.

[Bertron]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

so I tested a connection called CN1805 that goes from the power board to the main board with readings as follows:

INVERTER ON/OFF...................0.038V
NC.......................................0V
PWM DIM..............................0.425V
GND.....................................--
DET_5V.................................5.13V


is that voltage way too small for the INVERTER ON/OFF signal? I have no idea what it should be. Thanks again to everyone helping me out with this, I am certainly learning a lot.

EDIT: from an older post here (https://www.badcaps.net/forum/showthread.php?t=51026&page=1) it seems the INVERTER ON/OFF signal should be greater than 2V to turn the backlights on. The same thread suggests replacing C102 on the main logic board. I think I will attempt that now and see what happens.

[Andrew F. Ali]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

Yes that is way too low. You could try measuring the INV-ON/OFF with the jack disconnected. It may be instantaneous so you would have to connect the DMM then power up as it might go high and then drop low as it's not connected to anything. If you get positive result then there could be a short on the Inverter section causing it to go low....If it is negative then there is an issue with the Main Bd.

[Bertron]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

so I replaced C102 on the main logic board and the television still does the same red blinking and clicking on the power board. When I try to power it on with the remote, the red blight strobes/blinks rapidly as if it knows im pushing the buttons, but I still have a complete lack of backlight. Could use some more suggestions.

[attainteddragon]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

if you disconnect the main from the ps, the backlights should come on. that is if this is one of the sets that has built in pull up resistors. otherwise, you would need to use a couple of 1k resistors. if the backlights work, you will need to look further into the main, or replace it.

[Bertron]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

dragon, I have tried disconnecting the main from the power supply and the backlights do not come on. How would I use the 1k resistors, exactly?

[attainteddragon]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

disconnect the cable to the main board. i remove it at the main end, then use the end of that loom to place 1 resistor between stby and the ps/on pin.
on (what looks like cn803, in your pic), place the other resistor between inverter on/off pin and any of the active 5v lines. back lights should come on, but without any pic since the main is now disconnected.

you wont need to press the power button with the resistors in place, it will power in automatically when you plug it back in.

[Bertron]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.



So I tried what you suggested with a 15kohm resistor and the backlight still didnt come on. I did notice a very faint squeaking coming from the 'HOT' side of the power board that I normally don't get. I made sure the resistor made good contact with the connector and even tried to unplug and replug the power back in. No success. What does this tell me about what steps I should take next?

Thanks again, without help I would be totally lost.

[dskall]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

15k is way to much resistance

[attainteddragon]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

have you got a resistor closer to 1k?

that first resistor should turn the ps on. are your other output voltages there?

if they are, then add another 1k resistor between 5v and bl/on.

[Bertron]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

I'm a dolt. The resistor in that picture is actually 1.5kohm, not 15.

anyway, I tried a 15 ohm resistor in the same configuration and I still didn't get a backlight.

[attainteddragon]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

have you jumped the bl/on pin yet?

[Bertron]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

ok I put back the 1.5kohm resistor and here are the results I got from each connection with the 1.5kohm resistor in place and the TV plugged in:

CN801
PSON...............3.75V
SYNC...............0
STB.................5.17V
13.0Vs.............13.31V
5.1V.................5.1V
13.0Vm.............13.21V

CN1805
INV ON/OFF.......0.001V
PWM DM...........0V
DET_5V.............5.17V

CN1806
FB...................0V
FB...................0V
GND.................NA
GND.................NA
LD...................11.51V
LD...................11.51V

sorry again for the earlier mixup.

DRAGON: I am not sure where the BL ON pin is on this set

[attainteddragon]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

yours in marked inv on/off.
this is the inverter on control

[Bertron]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.


AHA. After connecting the 1.5kohm resistor to INVERTER ON/OFF and DET_5V the backlight came on for 5 seconds then a *click* and the backlight went off for approximately 15 seconds.... then it came back on for 5 seconds... then off, and on and off and on.

It doesn't stay on solidly, but it's good to know that the backlight at least works.

I hope this sheds some light on what direction I can take on the repair. Thanks!

[attainteddragon]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

check what voltage you have on the inv on/off pin. it should be staying on.
i'm guessing that a voltage will be dropping out with the on/off cycling.

p.s. if you add pics via advanced, manage attachments, then they will show up as thumb nails and make viewing the thread easier. thanks.

[Bertron]

Re: Samsung LN52A550P3FX2A, blinking red light in front. No backlight.

steady 4.98V throughout on INV ON/OFF, except for when it clicks on and it makes a brief jump to 5.00V