Samsung won't power up ln32a450c1d

[simcole]

Hello again everyone. I was watching TV the other night and it was working fine. This morning when I turned it on, it won't power up. The standby light is ON and when I press power, the standby light flicks off, then on again (and remains on) but nothing happens. There is no picture or sound nor does the TV come on.

I have pulled the power board and I'm not getting ANY voltages except my 5V standby power off the "SB" pin that goes to the main board.

I downloaded the service manual but there is a major problem. All the troubleshooting and diagrams have DIFFERENT numbers and names than what's on my board. My power board is a BN44-00214A. I've pulled EVERY capacitor including the big one out of the board and bench tested it. They all check OK. The Blue capacitor on the board is also ok.

Are voltage loss % around 2-3% mean the capacitor is bad?
Here are some readings:
CM861 - 3677UF 1.8% Voltage Loss
CM868 - 697UF 1.3%
CM858 - 678UF 2.5%
CM856 - 470UF 3.6%
CM582 - 682UF 2.0%
CM851 - 695UF 1.3%
CB852 - 2076UF 1.5%
CM808 - 17.7nf 17ΩESR

I checked the solder joint on the (transistor/bridge??) QB802 and it looks fair. I manged to scorch the board near there too. I pulled it and cleaned it and added my own solder. I haven't tested it yet except out of circuit and with my MM. With Red prong on left lead and Black prong on right lead (nothing in middle) in diode mode I get .62. I don't get readings any other way or combination.

I'm getting NO DC voltages anywhere else on the connector pins that go to any other part of the TV. I'm not getting 24V or my 12v or my 5.3v etc.

How do I test that QB802 and what else do I need to check. I DID scrape all the glue off all major components. I also checked the big cap but forgot to write the values down, but they were within the 10% limit.

I referenced the service manual and see the flow chart on page 4-2 says step 2 to check 5V at D1001. I don't have a D1001 on my board.


I attached a clear well lit picture.
Has anyone had similar problems with this unit and manual? I searched the forum and saw the same model TV having problems, but my problem is different.

[tom66]

Re: Samsung won't power up ln32a450c1d

Lots of issues with this PSU, caused by bad glue.
https://www.badcaps.net/forum/showthread.php?t=42422

Were there burn marks around QB802 there before?

[simcole]

Re: Samsung won't power up ln32a450c1d

Yah I saw that thread. There was no burn marks before. With no voltage anywhere else I'm leaning toward checking transformer or ic but I don't have a manual that lined up.

[jetadm123]

Re: Samsung won't power up ln32a450c1d

This schematic of the power supply might help. Are you getting the PS_ON voltage at pin 1 of CNM802 on the power supply board?

[simcole]

Re: Samsung won't power up ln32a450c1d

This schematic of the power supply might help. Are you getting the PS_ON voltage at pin 1 of CNM802 on the power supply board?

Thanks for the schematic. I'm gonna go look at this now.

No I'm not getting any voltage at PS_ON on pin 1. I DO get 5v at pin 3 though, which is the ONLY voltage I get out of that entire connector.

[flocko]

Re: Samsung won't power up ln32a450c1d

Pull the plug from power board to main at main board end, with a 500-1000ohm resistor jump stby to Ps on(pin 3-pin 1) the board should now show all supply voltages. if you see it is working your problem is with the main board, if not its power board. hope this helps Flocko

[simcole]

Re: Samsung won't power up ln32a450c1d

Pull the plug from power board to main at main board end, with a 500-1000ohm resistor jump stby to Ps on(pin 3-pin 1) the board should now show all supply voltages. if you see it is working your problem is with the main board, if not its power board. hope this helps Flocko

Hi again. So I did like you said and jumped the pins. All power connections came alive and read the voltages they were supposed to. AMAZING! I guess this means there is something on the power board that's bad. Specifically something from the input voltage to the pwr_on voltage? Where do I look now that I know this?

[vinceroger69]

Re: Samsung won't power up ln32a450c1d

The fault is on the mainboard the power supply seems fine as its giving the correct voltages now
What is the mainboard number?

[flocko]

Re: Samsung won't power up ln32a450c1d

Hi you have a problem with the main board as it is this board that turns on the power board, the 5v stby from the power supply goes to the main , when you use the remote or side buttons to turn the set on, it returns a voltage of about 3v to the PSon pin . that was why you were asked to check for life on pin 1, faults to main boards are hard to trace, so I would look for a replacement, the part numbers for Samsung mains are on the white bar code sticker and need to match like for like look up the number you find on shopjimmy , as some time you can use other board numbers as well Flocko

[jetadm123]

Re: Samsung won't power up ln32a450c1d

Post a good focused photo of the mainboard. Wouldn't hurt to check for basic things like: fuse (if any) and voltage regulators for proper output.

[Alastair E]

Re: Samsung won't power up ln32a450c1d

Has this got a Bordeaux Mainboard...?

[simcole]

Re: Samsung won't power up ln32a450c1d

Hi you have a problem with the main board as it is this board that turns on the power board, the 5v stby from the power supply goes to the main , when you use the remote or side buttons to turn the set on, it returns a voltage of about 3v to the PSon pin . that was why you were asked to check for life on pin 1, faults to main boards are hard to trace, so I would look for a replacement, the part numbers for Samsung mains are on the white bar code sticker and need to match like for like look up the number you find on shopjimmy , as some time you can use other board numbers as well Flocko

SO I SCREWED UP. I (incorrectly) assumed when you asked for voltage on the pwr on pin (pin1) that I was checking with it unplugged from the main board. I assumed power came from the power board even unplugged. I was wrong. So when I test pin1 while pressing the power on button I get 3.5 volts, which drops to 0, then back to 3.5, then back to 0 and stays 0.

I'm sorry I led everyone astray here. If the main board IS sending the 3.5 volts when commanded, but its not coming on, I still assume power board.

[vinceroger69]

Re: Samsung won't power up ln32a450c1d

as per flocko post 6 retest like this, Pull the plug from power board to main at main board end, with a 500-1000ohm resistor jump stby to Ps on(pin 3-pin 1) the board should now show all supply voltages. if you see it is working your problem is with the main board, if not its power board does pin 1 now stay a stable voltage?

[flocko]

Re: Samsung won't power up ln32a450c1d

Yes I could see from your first post that you must have a return (PSon) from main board, as you said you had a blinking red light to the front of the set, but this can happen with a bad power board as well , so the power board test tell me its working and that your fault is with the main board ,as already said take white barcode number go to shopjimmy.com put that number in it will gave you a list of boards you can use, with this model I think you have a lot of subs, then with your list of numbers check out ebay or give to call out on here for a board . Hope this helps Flocko

[MacAddict]

Re: Samsung won't power up ln32a450c1d

I don't mean to but in but I have the same power supply board that is having a similar problem except the stand by red light is on but the briefly flashes. The cycle time seems to be ON for 10-12 seconds and OFF for 3 seconds. All of the power readings are good but something is causing a restart, any ideas? This was a set I bought cheap with the intention to repair but I new to the electronics trouble shooting.

[newtothis]

Re: Samsung won't power up ln32a450c1d

Have you jumpered the PS-ON to Standby as above and got all correct voltages at the connector? If so your main is at fault so replace

[MacAddict]

Re: Samsung won't power up ln32a450c1d

I did not see a voltage change when pushing the on button. It stayed at 5.37 v until the red standby light on the front flickers once and the voltage dropped and everything started back up again. On the main board there is an optical sound plug that shines red. The light stays on for 10+ seconds and then is off for 3 seconds as if the system is rebooting. I also replaced 2 SR104B diodes on the power supply board because they were reading .204 v out of circuit but reading .972 one way and .178 the other while in circuit but that did not help. Like I said, I am new to this and trying to learn but some things just don't make sense. So if the correct voltage is going to the main board and it has a fault then it sends a signal to restart the system? Or would it be a chip or relay (?) that would detects a power problem and restarts the system?

[flocko]

Re: Samsung won't power up ln32a450c1d

Try reading posts 6 and check this for your self Flocko

[newtothis]

Re: Samsung won't power up ln32a450c1d

I did not see a voltage change when pushing the on button. It stayed at 5.37 v until the red standby light on the front flickers once and the voltage dropped and everything started back up again. On the main board there is an optical sound plug that shines red. The light stays on for 10+ seconds and then is off for 3 seconds as if the system is rebooting. I also replaced 2 SR104B diodes on the power supply board because they were reading .204 v out of circuit but reading .972 one way and .178 the other while in circuit but that did not help. Like I said, I am new to this and trying to learn but some things just don't make sense. So if the correct voltage is going to the main board and it has a fault then it sends a signal to restart the system? Or would it be a chip or relay (?) that would detects a power problem and restarts the system?

If the main is at fault it will keep rebooting the system while plugged in, We need to omit the main from the equation and put a dummy load on the PSU to start the PSU up. The mainboard receives 5v STBY from the PSU, The main send power to the PS-ON pin when the power button is pressed... This turns the PSU on and gives all other voltages. So.... We need to see what voltages you get without the mainboard

Not all components can be checked while in circuit... If they read fine out of cct they are fine.

[MacAddict]

Re: Samsung won't power up ln32a450c1d

Okay, I unplugged the 24 pin power ribbon from the main and added a 680 ohm resistor from pin 1 - 3 and read the 5v pin on the start up connector on the power board. The voltage now reads a steady 3v and the power does not go through a restart cycle. Pushing the power button had no effect on voltage. Checking the connections to the inverter revealed steady and accurate voltage. Is the 3v correct and enough to send a start signal?
So it looks like there is a problem with the main board, correct? Is there a way to isolate the component(s) on the main board so I can replace them? Remember, it is not about replacing major part but the quest to find what went wrong and fix it, then pushing the power button... IT'S ALIVE!