SOLVED--Samsung 850HW-YD03 power up issue - Page 1
Forum section: electronics / repair

author: Doc38343
author_rank: Contributor
timestamp: May 22, 2015, 06:43:25 am
content: Hi Guys,Love this forum and am a novice to electronics repair but i need to fix this TV since it has become my nemesis. Thanks in advance for any help you may be able to share.First open and look inside, tested the obvious fuses and there were several. Found one blown up between the two main middle heat sinks. I continue to examine for a cause and saw a vented cap on the HV board to the right side (the one the plasma screen ribbons go into.) so I made sure the caps were discharged and replaced the swollen one. I tested things in circuit as best I could and everything else appeared ok. (i had not seen the remove from circuit video at that time) I then replaced the fuse and as I was about to test i thought to give it another good look to see if anything else was bad. I found 2 diodes on the power supply, not far from the fuse that was blown that had burnt out and were dead shorted. They got hot enough to brown the board slightly. I replaced them with the exact same kind and tried to test all the other diodes in circuit and all appear ok.I put the board back and decided to give it a try. When I plugged in mains I saw a green led lit solid on a small board solder pinned into the main power supply board (looks like some type of analysis point) anyway I think this is a good sign so I test the standby voltage and it is 4.89V which is probably correct for 5v allowing for my lack of a good meter. so I press the power button. I see the green on light and hear some relays click and then a second click about 1.5 seconds later. Nothing.... then after about 10 seconds the power light goes out. Also I noticed that the little board attached to the main power supply led was now blinking and it keeps blinking. i wait a few and then try the power button again and this time no relays click either.So now I unplug the set and allow it to discharge for a while. I examined things again to see if i overlooked something to no avail. So I plug it in and try the power again, Same thing. I did notice the little board led was solid lit right up until i pressed the power button and the relays clicked on then off. I decided to test this again so I unplug, wait, then plugged back in only this time I waited for a long time before i pressed the power button and the led on the little board stays solid up until i press the power button.I suspect the shorted diodes damaged something more but apparently it is not in the low voltage section 5v standby is good but when those 200V relays trip something pulls them right back out . Oh yeah i did try it with the boards to the right and left that have the plasma ribbons disconnected and exactly the same sequence occurs no change.I know i'm a noobe so be kind..... I want to learn not quit on it. I could buy boards but whats the fun in that!! LOLThanksDoc

author: Hagis2k
author_rank: Regular Contributor
timestamp: June 01, 2015, 01:17:56 pm
content: First start with taking some quality photos for us to look at from both sides.Try to find a schematic of the set if possible, then start measuring all the voltages 3.3-5-12V and so on make sureyou do not miss any needed dc voltage, if then you confirmed that all voltages are present you might wonder if theeeprom failed or got corrupted its located on the video processing board.I have a 40" lcd tv from samsung with the same fault repaired the psu and now i will change eeprom.Good luck and if your not using a isolation transformer be careful! put the negative cable on the chassis somewhere with a crocodile clip or sothen measure the dc voltage with one hand behind your back it is an old school safety tip.

author: Doc38343
author_rank: Contributor
timestamp: June 02, 2015, 02:28:03 am
content: Thanks for the assist and the advise.I was about to post some photos when i decided to do a google search for the PS Board PS-50 W3-STD. I can buy one for $139 but heck whats the fun in that!!I found much info and a forum with several folks with the exact same issue, blown fuse at F8201, burnt diode/s at D8301 and D8302, and what do ya know WAALA! the only part I haven't changed and didn't know how to test yea olde MR4030 at U8301.I had mustered up the courage to finally test the board live. (I saw Daves video about cheap meters and so I borrowed a Fluke from my buddy) I have the 5V rail just fine but thats it. 12v and none of the high voltages. I even got so brave as to have my wife press the power switch while i was on the VS 200v test point to see if anything passed those relays... nothing. May have heard a cricket chirp... just kidden. i am fairly satisfied it is the MR4030 (its name is too long to type but it supply's control and standby voltages for most of the other devices on board) I ordered a 5 pack off the slow boat for $10 so perhaps in a couple or 3 weeks i'll have an update. Sure beats the crap out of $139 and in actual time spent on it so far, heck i think i've spent more on here typing...For the time being back to the learning board... making me a decent functioning ESR meter from junk around the shop and getting me a bench power supply together... from junk of course! I got tons of it here since it is a computer shop. I just recently decided to switch roles from a parts swapper to an actual fixer and son, this is WAY more fun! (It all started when i decided to make my own door open chime... got hooked!)Thanks to all the fine folks who help guys like me!

author: Hagis2k
author_rank: Regular Contributor
timestamp: June 03, 2015, 11:30:03 am
content: Nice with some progress yesAnd i agree with you why spend $139 if you can replace a couple of faulty components?I would use the multimeter and check the transistors and diodes for dead short sometimes you need to desolder one leg to be able to get a accurate readingson one 32" samsung i worked on i had a defective rectifier bridge, ptc (over current protection) and i also found out that the two mosfets that feed the backlighttransformer was blown they work in push-pull most often.And if you do not own a variable ac transformer you can always hook up a 60w incandescent bulb in series with the load, if you then see thebulb flash up and down in pulses that looks promising then the controller for the psu is alive. Or if it just lights up you have some moreproblems like shorts (and the best with using a bulb in series it gives you a cheap current inrush protection) better with a bulb that lights up thento see the new components you just replaced go up in smoke

author: Doc38343
author_rank: Contributor
timestamp: June 04, 2015, 04:32:27 am
content: QuoteThanks and please help me understand the bulb thing.... how do i connect it in series with the load, referring to before i replace the suspected device or after i have installed the new one. (saw something about using this method somewhere else also) and thanks because i do not have a variable ac supply yet. Am quite interested. I could make me a socket for this bulb to have on hand for testing on other projects as well.

author: tautech
author_rank: Super Contributor
timestamp: June 04, 2015, 11:31:12 am
content: Quote from: Doc38343 on June 04, 2015, 04:32:27 amIt's called a dim bulb tester, Google it.You'll need incandescent bulbs of various wattages to match different loads.Have a play with different appliances once you've built one to get a feel for how it behaves(lights) with different loads, especially at power on.Normally a sharp flash from charging of caps followed by a dimmer glow at DUT quiescent current load.Bright tells you something is wrong, but normally the magic smoke is retained.

author: Doc38343
author_rank: Contributor
timestamp: June 04, 2015, 04:35:07 pm
content: QuoteWhen I googled it i got a lot of info on testing older appliances and mostly radios. I was wondering if this would still apply or work on this plasma tv?It has a mains input filter and transformer board BEFORE the main power supply board. (Old guy on you tube said the bulb would not work in a case like that)Therefor I am thinking ok but for me to use one i will need to put a connector on it to get it inline before the board but after the input filter board.Attached photos of the input board and the power supply in question....

author: tautech
author_rank: Super Contributor
timestamp: June 04, 2015, 09:01:04 pm
content: Quote from: Doc38343 on June 04, 2015, 04:35:07 pmNo, put a bulb in series between a mains lead and a mains socket, then plug in DUT to socket.Make it in a box, safe and for future use.

author: Doc38343
author_rank: Contributor
timestamp: June 11, 2015, 03:36:52 am
content: Hey guys CHECK THIS OUT!!!! WOOOOHOO!It works! No greater feeling than when i pushed that power button and saw the blue input box floating around on the screen.Thanks for your assistance! This has really boosted my confidence for actually repairing the boards as opposed to replacing them.It also feels good to know the parts installed are better quality than what was removed..1. 5A Slow blow fuse2. 680uF 50v Low ESR cap (old one was 680uF 25v)3. 2 - 2N4007 Diodes4. 1- MR4030 (and I was able to determine it was "half working")Discovering the front says Sanyo "priceless" (the board I repaired is used in several models of plasma tvs)Actual work doing the repair about 1 hour if I include removing and replacing the back.(I am not counting the long wait time for the HR4030 to get here, and time spent learning!)No greater feeling.... as old Dave says "Like sex on a stick!"