Samsung plasma tv wont turn on - Page 1
Forum section: electronics / repair

author: EvilGeniusSkis
author_rank: Regular Contributor
timestamp: August 10, 2016, 03:06:10 am
content: I've got a Samsung plasma tv that won't turn on. when it is first plugged in there are 2 relays that click, the screen lights up but stays black for a bit then goes out, I've tested the power supply and it works, I can't find any blown fuses and don't see any obviously damaged components. I've thought things through and it seams to me to be either the input board or the processing board. Would i be correct in assuming that due to the lake of any menus ect. that the problem is the processing board?

author: poot36
author_rank: Frequent Contributor
timestamp: August 10, 2016, 03:27:03 am
content: It still could be the power supply is not working correctly under load and falling out of regulation. Do you have a scope to look at the ripple on the power supply lines? If not set your multimeter to volts AC and tell me for each voltage what you get on the meter.

author: EvilGeniusSkis
author_rank: Regular Contributor
timestamp: August 10, 2016, 03:52:07 am
content: Quote from: poot36 on August 10, 2016, 03:27:03 amCan't test right now as it's late at night but if this is the problem would it indicate bad caps?

author: Ijaz
author_rank: Contributor
timestamp: August 10, 2016, 04:08:11 am
content: Which model is this ? I did spend a lot of time in fixing Samsung Plasma TVs.Some Samsung Plasma TVs have builtin test function. To exclude the possibility of main board, you can disconnect the LVDS cable from main board to control board (the smallest one) and look for a jumper on the control board. Connect pin 2-3 (I hope I remember it correctly) and power up. This will start a self test on the display. If you see some patterns on the screen, then everything except the main board (with lot of video inputs) is the problem.I have rarely seen a main board going bad, most of the time it is the power electronics, either Y-Sus or X-Sus or the Y-Buffers.

author: EvilGeniusSkis
author_rank: Regular Contributor
timestamp: August 10, 2016, 04:35:32 am
content: Quote from: Ijaz on August 10, 2016, 04:08:11 amTV is a PN50B540S3F, I don't suspect the input board either. on the control board there are 2 loops that are soldered on, one is GND the other is labeled "test trig"[or something like that], so i just short them, plug the tv in an see what happens?

author: BMack
author_rank: Regular Contributor
timestamp: August 10, 2016, 07:54:34 am
content: Quote from: Ijaz on August 10, 2016, 04:08:11 amIt's pin 3 and 4. It might be holes or pins, there will be four in a square configuration.

author: Kilrah
author_rank: Unknown
timestamp: August 10, 2016, 08:00:15 am
content: Check all the supply voltages' DC levels and ripple.Had nightmares with a TV back in the day because the PSU's 5V rail was a tad low, and caused the mainboard to only occasionally start up properly.

author: poot36
author_rank: Frequent Contributor
timestamp: August 11, 2016, 03:56:45 am
content: If my test shows more then a few volts AC on the higher voltage lines and more then 250mV on the low voltage lines I would start suspecting the caps. The fact that you hear the relay click twice probably means it is dropping out due to not enough voltage to keep it on. I have had caps go bad but look visually fine. One was on the output of a linear voltage regulator for a LCD computer monitor that caused the main control micro to lock up and the monitor to try and turn on fail and then not be able to turn off or respond to any signal or button input.

author: EvilGeniusSkis
author_rank: Regular Contributor
timestamp: August 15, 2016, 09:42:31 pm
content: Quote from: poot36 on August 11, 2016, 03:56:45 amThere are 2 relays.

author: poot36
author_rank: Frequent Contributor
timestamp: August 16, 2016, 06:45:03 am
content: Doh! I misread that as 1 relay clicking twice. Before the TV broke how many relay clicks where there at power on? When you turn on the TV does the startup sound play (if so equiped and turned on in the menus before the fault)? Have you measured any of the local regulators on the main motherboard? I would expect at least around 12V for the sound amp, 5V, 3.3V for logic and maybe 2.5V and 1.8V as well for memory or core logic in some of the chips. If all else fails try using a heat gun on any of the large bga packages or reflow the entire board in the oven.

author: EvilGeniusSkis
author_rank: Regular Contributor
timestamp: August 27, 2016, 07:57:03 pm
content: Quote from: poot36 on August 16, 2016, 06:45:03 amI got it broken so I'm not sure about the # of relay clicks or weather the start up sound was enabled. was getting 1VAC on 15VDC rail.

author: poot36
author_rank: Frequent Contributor
timestamp: August 28, 2016, 01:46:38 am
content: If you were getting 1V AC on the 15V DC line I am going to suspect dried out caps on that line. Try disconnecting everything from the power supply board except for the board that the power switch is connected to and re-measure all the rails on DC volts and AC volts and report back.

author: grifftech
author_rank: Frequent Contributor
timestamp: August 30, 2016, 03:29:58 pm
content: just buy a new TV