Step 3: Testing the Power Supply

Static Electricity Warning
Some components on the power supply are CMOS integrated circuits and are therefore sensitive to static electricity. Before touching the circuit board, I make sure the TV is unplugged. Then, I touch a piece of metal on the back of the TV that is grounded, i.e. part of the metal frame or one of the mounting screws or mounting posts of the power supply board. This will dissipate any stored static electricity by the body and discharge it to ground. CAREFUL!!! This should only be done with the TV turned off and NOT plugged in. Otherwise, one might touch something with HIGH VOLTAGE and receive an electrical shock. In particular, stay away from the large heat sinks with the yellow stickers on them indicating high voltage.

The power supply is the large circuit board in the middle of the TV. It has many transformers, large capacitors, and a couple IC's. There are eight connectors attaching the power supply to the other circuit boards on the TV. Looking closer, one can see that the power supply(Model#:PSPF651B01A) is manufactured by Samsung, as is the plasma screen itself. The supply provides about ten different voltages; 190V, -180V, 60V, etc for the plasma screen as well as 3.3V, 5V, and 12V for the logic and digital electronics.

The power supply circuit board contains a wealth of information including its part number and a table of the different voltages it produces along their signal names(Va, Vscan, Vstb, etc). Test points for all these voltages exist on the left side of the board(looking at the power supply as it is mounted to the back of the television).

How to test
I used a multimeter to probe the voltages at the testpoints with the TV turned on. BE CAREFUL!!!! This is of course highly dangerous as HIGH VOLTAGES occur on the power supply and the TV was not meant to be run with the back off. Touching certain points on the power supply while it is powered can KILL YOU!!!! To be safe, don't touch ANYTHING inside the TV whilst it is plugged in. In fact, if you do not know what you are doing, just stop here. No point killing yourself over a stupid TV.

If you dare....
The RTN node (seen on the silkscreen at the top left connector(and others) ) is basically the common grounding point and is connected to Earth ground, the shiny metal backing of the plasma screen, and all the metal mounting pegs that the power supply is mounted to. The black or negative lead of your multimeter should be attached to this point. I just stuck the black probe into one of the mounting studs and let it hang there (out of the way) so I could probe using the other(red) lead of the multimeter with one hand.

Start off with the TV unplugged and turned off. Attach the negative or black lead of the multimeter to any mounting stud near the power supply board. Now plug in the TV and make sure nothing explodes. Now turn on the TV with the remote control and again make sure nothing explodes. Is the screen blank? If so, good. You'll be able to probe the test points on the power supply to determine which voltage is not being produced. In my case, it was Va which is supposed to be 60V. Make sure to make a good contact between the testpoint and the multimeter probe. If the contact is poor, the voltage readout may look as though it is fluctuating between the spec'd voltage and some lower voltage. For example, if the spec'd voltage is 180v, not pressing hard enough to connect the probe and the testpoint may result in a readout that wanders between 180v and 50v.

If all the voltages are being supplied and withing spec (as shown on the power supply's silkscreened voltage table shown in the fourth picture below), your power supply is most likely functioning correctly. Your problem may lie in a different area. Numerous people have mentioned a problem with their Y-Buffer, the circuit boards flanking the left and right sides of the plasma screen. Specifically, whitby905 (see the comments section) has found that the lower left Y-Buffer board was contacting the metal plasma screen backing and had shorted out. If your power supply checks out, look and smell for any indication that any of the Y-Buffers have shorted to the case. You may have to remove them and look on the back for shorted solder points. I don't have any pictures of this situation besides the one from whitby905 in the comments section.

My problem was with the Va voltage of the power supply so I will continue discussing it in the next section "Debugging on the Bench."
<p>I have a W4200HD (that's a 10 year old 42&quot; Plasma tv.)</p><p>It has worked perfectly for all these years. Now it starts clean then every few scenery changes and it develops a black imprint of the scene. Then stays behind and changes scene again and developes another imprint of that scene. It builds up until most of the screen is black. I can change the cable channel to the channel menu page, then back to what I was watching and it's all clean again. I have to do this every couple of minutes. </p><p>Any ideas?!!!</p>
<p>5 years ago, my W5001C failed (the VA supply was not working) and the info here helped me to fix it. Yesterday, it died again (same symptoms). I was eyeing a nice new 4K panel, but figured i give another try at fixing it. This time I found the D5V supply was low. The info in this thread helped me again, pointing me towards capacitors, and sure enough mine looked to be bulging a bit. A quick run to Radio Shack and i had some replacements. They didnt have 2200uF 10v, so i had to use the much larger 2200uF 35v. The Dell is up and running again. I'm happy i'm not throwing a 50&quot; plasma into the trash, but sad I'm not upgrading to a nice new UHD panel. </p>
Just curious as to whether or not this is still a live topic? <br> <br>I bought my Dell W5001C brand new from the Dell site and when it was delivered, I was like a kid again. Then 1 year later, almost to the day, and of course the warranty had expired, it went out. All the symptoms explained above. No screen but sound, blue power LED was lit. I would turn it on, it would give the audible click and then almost immediately another click. I thought it might be one of the power relay switches, but, after paying $5000.00 for this thing, I wasn't about to attempt it myself. <br>I called Dell and of course they wanted the thing shipped to them via insured courier to their buildings in the Bay Area of California. All at my expense, mind you. Then I would have to pay a large fee for just looking at it, to be followed up with the repair and replacement of any parts, etc., etc. <br> <br>After looking into doing as they asked, it would have cost me in the neighborhood of $1300.00. Just to have them look at it. <br> <br>I quickly packed the thing back into its box and stored it away. For almost 3 years. <br> <br>I saw an ad in eBay for the repair of my TV for $150.00 one day and got all excited again. The draw back was that I would have to disassemble all of the boards from the TV and send them to this guy in San Jose, California. After 3 years, I thought...&quot;Well ...It's already broken, what could I possibly do to it?&quot; <br> <br>No... I didn't hurt anything. <br> <br>He sent the boards back to me about 4 days later and I reassembled the TV... and it worked beautifully. <br> <br>For almost 1 year EXACTLY to the day. <br> <br>Now the same problem. <br> <br>When I got the boards back, I looked real close to what might have been replaced. The only thing I could see was that he had replaced 3 or 4 capacitors on the main PCB. <br> <br>I am going to attempt this on my own this time, but, I am really hoping that this is not a dead thread just in case I need some backup. <br> <br>Are you game, mr12volt??
I still monitor the comments to see if I can be of help. Just keep in mind that these tv's can fail in a number of different ways. Make sure the first thing you do is measure the voltage on the Va test point on the power supply board. The solution I detail will only work if the Va voltage is zero. I get emailed when someone posts a comment so if you have any further questions I will see them. <br>By the way my buddy's TV is still going strong.
<p>I know this is a really old post, but i found a dell 4201c on the trash the other day its looks in really nice shape. i opened it up and see no capacitor damage. it turns on with one click, all 3 led lights on the phillips board stay on but the screen does not come on. the blue power led comes on, and will turn of if i push it again with one click, then one green led stays on. i did notice some burn marks around some components of what seems to be an amplifier board for the speakers. its the small board right about where the silver power supply box is. i thought this would be a low risk project with changing the two capacitors for the coppell tv repair post. can anyone help</p>
<p>Not sure you can help, but our Dell plasma tv/monitor works just fine but the speakers went out! My son has decided to try replacing the mini-banana plug connections and we can't seem to find them small enough. The typical &quot;mini&quot; is too large. We REALLY hate to let go of this tv just because the speakers aren't working! You'd think we could just replace with other speakers but my son says no, it can't be done. Any thoughts?</p>
<p>I had a completely different set of speakers hooked up to my Dell at one point with no issues. I don't know why he is saying it can't be done...</p><p>On another note, I bought the original OEM speakers that came with the TV on Ebay for $5.99 brand new. If it is just the speakers being bad, that is your best route, in my opinion.</p>
<p>Here I am... A year later and still haven''t gotten to my Dell... But this is the weekend!</p><p>I've researched and researched and it turns out that the 5v power problem seems to be a universal one. The W4201 and W5001 plasma TV's from Dell from 2005-(2007 I believe) were manufactured by Samsung and packaged as Dell. All have the same failing. Which is why they were discontinued for a while... Lol... Apparently, Dell is offering the 42&quot; again, and these are getting 4 star rating reviews from places like PC Mag and others... Hind sight is 20/20, eh?</p><p>Ok... </p><p>So I am going to open her up tonite, run some prelims and then I will be talking to you right after. If not late tonite than first thing tomorrow for sure..</p>
Hey guy im in ur same boat, and about to attempt this myself...SHOULD I STOCK UP ON THIS PART...LOL...LET ME KNOW WHAT HAPPENS WITH YOU...CALL ME INSTEAD I NEED A COACH ALSO 9063762433...THE NAMES KIM
<p>i know this is a really old post, but i found a dell 4201c on the trash the other day its looks in really nice shape. i opened it up and see no capacitor damage. it turns on with one click, all 3 led lights on the phillips board stay on but the screen does not come on. the blue power led comes on, and will turn of if i push it again with one click, then one green led stays on. i did notice some burn marks around some components of what seems to be an amplifier board for the speakers. its the small board right about where the silver power supply box is. i thought this would be a low risk project with changing the two capacitors for the coppell tv repair post. can anyone help?</p>
<p>Just in the off chance anyone may need some further technical info for this TV.. I happened to finally find a repair manual for it. It was listed as Phillips system... not a Samsung, as the board clearly states.</p><p>I added it to my Dropbox account so anyone can download the PDF file.</p><p><a href="https://dl.dropboxusercontent.com/u/62863468/philips_sdi-pdp_s42sd_yd09_s42ax_yd02_s50hw-yd01_repair-manual.pdf" rel="nofollow">https://dl.dropboxusercontent.com/u/62863468/phili...</a></p>
<p>And here is a newer(updated) version of the service manual...</p><p><a href="https://db.tt/ySmiiuxt" rel="nofollow">https://db.tt/ySmiiuxt</a></p>
<p>My 50&quot; unit has been down for almost 3 years (a 2006 serial Dell). I can't thank you enough for finding the manual. What a great thing to have. With no parts list I purchased a replacement power board from a tested vendor on E-Bay for 40 bucks. It shows up in a few days. When it does I will send pics and info on the registration and setup. The crucial part as with any set is having the right video output for high def (most computers do now) and having the right image files for true resolution. The resolution files are freeware now but a good primer on use and free files is at </p><p><a href="http://www.videouniversity.com/articles/color-bars-and-how-to-use-em/" rel="nofollow">http://www.videouniversity.com/articles/color-bars...</a></p><p>I am not associated with them and I am not selling anything. I hope this helps.</p>
<p>Well, I'm back two years after fixing my W5001C (see below). I had two caps on the PS board go bad (bulging) in the 5v circuit and replaced them. TV has worked great since.</p><p>Today the Mrs. Was watching the TV, muted it to look down at her computer, heard a click (relay?) and looked up to see a blank screen. I've cycled power a few times, unplugged and plugged it back in. Nothing.</p><p>Blue LED in the power button lights up when it's turned on at the power button, but no splash screen and no audio nor video.</p><p>So I've taken the set down to open it up for a visual inspection and to measure some voltages. I'll report back what I find, but if it's nothing obvious or something I can't or don't want to pay to fix, I may be off to Best Buy for a new TV.</p>
<p>The remote works to power the TV on and off. Not sure that was the case before. TV also turned itself off while I was looking at the insides&hellip; about 1/2 or so after turning it on.</p><p>All voltages seem OK, although the 5v line is at 5.2v. Not sure if that's enough of a difference to matter. (Thoughts anyone???) </p><p>There is also a slightly bulged capacitor (C619) that looks to be part of the 5v line. It's as bulged as the two I replaced two years ago to fix the TV, so it makes me suspicious.</p><p>So, I guess I need to decide if it's worth pulling the PS and that capacitor and replacing it. No good electronics stores in the immediate area. A good hour drive.</p>
<p>* 1/2 hour or so, that is. It shut itself off a couple of times.</p><p>Anyway, we decided that if this TV is going to fail more and more, we'd replace it. Got a new 60&quot; LED/LCD set. Getting used to the difference between LCD and plasma... it'll be fine. ;)</p><p>Still going to try to fix the Dell and maybe use it in the bonus room or give it to one of the kids. Will pull that once bulged capacitor from the PS and replace it and go from there, but not going to spend too much time or effort on it.</p><p>If anyone has any thoughts on whether the 5v test point reading 5.2v could cause issues, I'd love to hear from you. Thanks!</p>
<p>Any luck with your Dell, <a href="https://www.instructables.com/member/TJNoffy/" rel="nofollow">TJNoffy</a>? </p><p>Sounds exactly like the problem I am having. Power looks fine on the board. Have you checked out the X and Y buffer boards?</p>
Any luck with yours ??????
<p>Actually? No. I have gone as far as my limited ability in advanced electronics troubleshooting and diagnostics as I am able. I have linked all of the pro service manuals I was able to dig up on this TV in this thread already, but, here they are again.</p><p><a href="https://db.tt/TjJTP2Oj" rel="nofollow">https://db.tt/TjJTP2Oj</a></p><p><a href="https://db.tt/ySmiiuxt" rel="nofollow">https://db.tt/ySmiiuxt</a></p><p>Hope these might help..</p>
Ok so digikey sent me the wrong god damn part....how much more frustrating can this be. .....
Thank you so much im glad to have help
<p>I finally got tired of looking at the broken TV in the dining room, and with a new TV on the wall now, I lost interest in pursuing it. I got a couple of extra years out of it for $3, so I'm calling that a win. The Dell went off to be recycled at Best Buy.</p>
<p>Lol... I understand. I am, unfortunately, a devout hoarder. I have gotten a grand total of 2 years of service from this $6,000.00 paper weight and I am bound and determined to get my moneys worth! One way or another...</p><p>Thanks again!</p><p>Cheers!</p>
Can someone help me on this topic when ny parts come in ??????? JUST REPLY AND I'LL GET BACK TO YOU FIR HELP...THANK YOUSSSSS
My dell 42 inch plasma w5001c has no sign and the picture has squegly lines can someone tell me which boards to replace? Thank you
Did you read the inquiry above...same thing..https://m.instructables.com/id/Dell-W5001C-50quot-plasma-fix/
<p>Yeah... I am at a loss...</p><p>Everything checks out as far as power is concerned... no visible burns or rubs on the buffer boards. I know this doesn't rule out the possibility that the buffer boards may be bad, however. This is one of the OTHER common failings in this $6,000.oo lemon.</p><p>Yes... I paid $5,999.99 for this thing when it was first released. I am considering getting a tattoo on my forehead that says &quot;SUCKER!&quot;</p><p>I guess I will just break down and pull it apart and send the boards off like I did the first time. I just wish I knew how to check the buffer boards themselves to see if they are bad. I see new X and Y buffer boards come up for sale all the time on eBay for around $20.00 each.</p><p>Thanks for your help and patience, mr12volt. I truly appreciate it.</p>
<p>Maybe you aren't following this post any longer, mr12volt?</p>
Hi No1sBoy, I'm still following along and hoping you make progress so we can all learn from your experience. Unfortunately I don't think I can be of too much help. My experience with the failure modes of plasma screens is limited to the write-up you see here. If your power supply voltages are all within range, I'm at the limit of what I know about fixing plasmas. I can only speculate on the rest. You may indeed be looking at an X or Y buffer. You could also be looking at an issue with the digital logic board that sends the video to the buffer boards. I would probably get an oscilloscope and probe the flex cables going to the buffer boards for video data. At least you can verify that it is trying to drive the buffers or not. Don't assume that your problem this time is the same as when you sent it for repair last time. In any case, good luck.
<p>I did a close visual check of both buffer boards..... And I can see no rub spots, blackened or dark brown spots where there might be burns or shorts. Nothing seems out of the ordinary..... I don't have an oscilloscope, unfortunately. However... I have always wanted one!! Could be a perfect opportunity to talk the wife into letting me???</p><p>If I am not mistaken, I do believe I saw one in the back of a local thrift shop for sale.</p><p>My Dell is still opened up and sitting in the living room. Worse case scenario is that I have to pull all the boards and send them back to the guy who did the work for me the first time. I just really wanted to see if I could do it myself this time.</p><p>I will get back to you......lol.</p>
<p>I've opened it up, inspected everything visibly possible, checked all the voltages via the silk screen printing on the back... All are within range. No caps are visibly bulging. </p><p>I am going to pull the X and Y buffer boards off next and see if I can see any visible shorts.</p><p>If there is nothing visible, I will then try and test the IC's..... </p><p>I was really hoping for a bad cap! Lol!</p>
Okay...weighing in here over a year later: Tonight, found a W4200HD on the curb across the street from my apt. Glass is all good. Set turns on for a brief period -- blue OSD. Then the display blanks. Eventually some relays kick off, and a red LED on ps board lights. So far, I've got the back off for visual inspection, which reveals four very large electrolytics; two of which (1000 @ 250v) are alarmingly swollen. The tops are so bulged out they resemble balloons. The other two (330 @ 450v) are only slightly bulged...one almost not at all. All the other caps on the ps board pass visual inspection. My initial impulse is to replace these four, before even attempting voltage checks. Will post back w/pix and results. Keeping my fingers crossed.....
jakdedert, When electrolytics age, they just dry out and loose their capacitance, they don't usually dome. The doming often happens because of an overvoltage or reverse voltage condition. I would suspect the diode bridges. These are the four pin relatively large IC's (probably attached to a heatsink) that take the raw AC and turn it into a pulsating DC signal of ~175 volts peak-to-peak. If the diode bridge breaks it could allow negative voltage to go to the 250V caps, which I assume are used to smooth out that pulsating ~175V signal. A power-factor-correction controller chip (in a DIP package) takes the 175V pulsating DC and pumps it into the 450V caps (through a large inductor) making a stable ~387V DC bus. Look at the large resistor that goes from the negative side of the diode bridge to the negative side of the large 450V capacitors. That is a current sense resistor and may be damaged as well. If the diode bridge failed, it may have taken the MOSFET switches with it too, OR the MOSFETs may have failed first and taken out the diode bridge. If it doesn't work after replacing the diode bridges and the domed capacitors, look at the MOSFETs. Be aware that replacing components without knowing exactly what has failed is possibly dangerous and could be expensive. If you replace the diode bridge and caps then turn it on and the MOSFETs are still busted, you could end up destroying the components you just replaced. Just proceed with caution. If you want to be as careful as possible, replace the PFC controller IC, remove all MOSFETs and test them (with a multimeter), and test the diode bridges. By &quot;test the mosfets&quot; what I mean is make sure that the impedance from the gate to source and impedance from gate to drain is &gt;1Megaohm and the drain to source connection is not shorted. Testing all of these would be a bit of a PITA because the pins are large and more difficult to desolder. Plus they are connected to heatsinks. If you handle the MOSFETs remember to keep yourself grounded so you don't zap them with static electricity. Best, mr12volt
Defective capacitors often fail in the manner I described. There are a lot of defective caps out there, due to the industrial espionage incident around ten years ago. Google 'Bad Capacitors' and among the nearly quarter of a million hits, read this: http://en.wikipedia.org/wiki/Capacitor_plague In any case, I replaced all the high-capacity/voltage caps on the main psb, and the set now works flawlessly. To be honest, I had planned to do more testing before slapping this board back in and firing it up; but given the difficulty in moving the set, I just went for it. So far, it's panned out. We'll see.....
Well that's embarrassing. Looks like I was 100% wrong on this one. Happy to hear that it was a simple fix. I guess I like to err on the safe side. How does one know before hand whether the capacitors failed because of a different component failure or because the caps were defective. If they are cheap parts, I suppose it's faster to just replace and pray. Just don't look at it when you flip the switch. Nobody like capacitor juice in the eyes :-)
The embarrasment is mine. The set failed again, as detailed above. I'm not sure if it was an incomplete fix (didn't replace enough caps), or there is a new fault...or possibly one related to the initial failure. I've considered shotgunning the entire ps board with new caps just to see if it would fix it, but the initial capacitor purchase was in excess of $35. More responsible procedure would be to do as you did and troubleshoot the board in a detailed manner. I'm not sure I have the chops, though.....
You never know. If I'd been being responsible, I'd have confirmed all of the voltages as soon as I fired this thing up. Where it sits right now (with the back still off), it's not really accessible. I'm still crossing fingers that nothing else is wrong; but I've dealt with the aftermath of bad caps before. I have a Dell monitor which is famous for the problem. There's even an instructable about it. Dell--or their subcontractors--was a particularly frequent victim; and this plasma was built right at the peak of the problem time...mid-90s. FWIW, you were 100% correct, had the problem been 'good' caps gone bad; but these are only five or six years old. The problem is particularly insidious because not all of those caps will self-destruct, and the ones which do, will do so at widely varying times. There are a lot of factors involved...the main one being; how marginal is the rest of the design.
The 4200HD that I had repaired three years ago by replacing bad caps on the ps board has failed again. The ps on this one has a 'tell-tale' set of lights on the board labelled with the voltages. When I power it up, they initially all come on except the 5v line. Then a relay clicks and they all go off except for one (assume that's a normal behavior when one section of the ps is inoperative), and the blue power light flashes. No picture is ever displayed. The set is stored now, but when I get into a new place, I'd like to get it going again. Any suggestions...anyone?
I tried posting a reply yesterday, but, for some reason, it wouldn't let me..? <br> <br>I am going to open her up either tonight or tomorrow, depending on how crazy my kids are acting..lol! Once I get a better picture of what I am dealing with, I will post again. I am thinking, after reading your very in-depth and intelligent Instructable here, I am not making a move without checking with you! Lol! <br> <br>Thank you for your time and you are doing an OUTSTANDING job here!
Greetings, <br> <br>Interesting thread and very informative, hopefully I can generate some more information on Dell W4200HD I am diagnosing. <br> <br>I have checked for swollen caps, and although none are obvious, needless to say, they could still be bad with age. <br> <br>It appears the same symptoms can be caused by more than one bad component. And it looks like one bad voltage will create same symptoms, so here is what I am seeing. <br> <br>When I turn on TV, the red LED comes on after the power up clicks in about five seconds or so, and this is consistent. I had sound go out first, then picture died, let it sit overnight, tried again, still no sound, and picture lasted for about five hours, then poof, nothing. I did run plasma conditioning for about five hours when I still had picture since a few areas of red and blue pixels were starting to shadow the lower left bottom with about a two inch area which you only noticed on white back screen. <br> <br>So here is what I have checked so far. Went through all the voltages, plugged in and TV off, and then turning TV on. I had VS 170V, VCC 15V, DSVL 5.2V, D3V3 3.45V, VSCAN 55.3V which is lower than 70V I believe it should be? But here is the killer, VE is 0V ???? Any ideas what to check and does the missing VE impact the low VSCAN voltage. <br> <br>Thanks,
This is a couple of years after the fact, but I just repaired my W5001C and I thought I'd share what happened...<br><br>Turned on the TV last week and no Dell logo splash screen or any other video. No audio either. After a couple of tries, the set came on and worked for a few days. Did this again a few days later. Finally the picture and audio died while watching it. The set also didn't respond to the remote (power on/off).<br><br>Thanks to this great instructable, I learned to check the voltages on the power supply. All were within specs except the 5v which measured at 3.0v - 3.5v.<br><br>I didn't think that the 5v being off would cause the loss of video, but could explain the lack of response to the remote by the logic circuitry.<br><br>After reading this: http://blog.coppelltvrepair.com/2010/10/dell-w4201c-hd-powers-on-off-no-picture.html<br><br>...I checked the two 2200uF 10v caps shown at this link. They were bulged at the top, and looked to be part of the 5v circuit. <br><br>Spent under $3 to replace the two capacitors. Set fixed!
And by a couple of years after the fact I mean a couple of years after mr12volt posted his experience. The above just happened to me...
mr12volt,<br /> <br /> So I thought I had the same problem with my tv as the one you described, however after replacing the ic I still experience problems. At first I thought it was working correctly however I think it must have been a coincidence. Ive checked the voltages and everything seems good except the 5v. After having the tv unplugged I read from around 3.5V all the way to 4.1V. The tv seems to work if the voltage does build up over 4.2 as sometimes it does. For the most part it doesn't seem to buildup from 3.5V to 4.2V.&nbsp;On pin 8 of U661 i read 4.98V which I believe is correct as Vref of the IC is suppose to be 5V after reading the datasheet on the uc2843. I had originally swapped out U501, and I ordered 2 extra IC's as they are only 1.23 cdn. So U501 and U661 both have UC2843B in them rather than the orignal KA3883's. ZD611 reads the exact same as the 5V output (after buildup stays around 4V) so I believe they are electrically connected, although I have not traced out the PCB. Would you think that the zener is bad? possibly pulling the 5v down to 4V? Any suggestions would be greatly appreciated, I don't have an isolation transformer to work with here only a DMM. I do know electronics, however without a schematic of this I'm finding it very difficult to troubleshoot. Thank you very much for the instructable, very well written.
@fvxtech - Did you every resolve the 5v and D3V3 issue? I'm having the same in my W5001C. I'm about to replace the two 2200 uF caps that are notorious for bulging/failing, and they look to be in the low voltage circuit of the power board. Just curious if you found anything else. Thanks
&nbsp;tcosman,<br /> First of all, please check back with us if you ever work out the problem. &nbsp;I don't think I can be of too much help since I don't have a schematic either. &nbsp;BUT! You have something almost as good as the schematic, the board itself! &nbsp;The board is only two layers so tracing the circuit isn't too bad. &nbsp;Use the DMM on continuity mode to track down traces that disappear under large components. &nbsp;Gradually you'll be able to build up enough of a schematic to figure out the topology of the 5V circuit. &nbsp;If you know electronics, you should be able to tell roughly what is a resistor, capacitor, transformer, diode, and MOSFET switch. &nbsp;The board is very well marked by its silkscreen and most of the symbols are pretty much there for you. &nbsp;They're even marked on the backside too! Brilliant.<br /> <br /> I'm kinda curious about the 5V and 3V circuits myself. &nbsp;I never looked closely at the digital logic voltages because that wasn't my problem at the time but now I wish I had. &nbsp;Many people seem to experience problems with them. &nbsp;I'd like to know the type of switching regulators used to produce&nbsp;5V and 3V , if they work off the ~400V rail just after the diode bridge or the +17V DC rail, which IC is the control IC for them, and if they are normally powered when the digital board is not plugged in to the power supply.<br /> <br /> Lastly, which 5V rail are you having problems with, the D5V or 5Vstb?<br />
I'm having the same problem as manuts, voltage problem isolated to Vscan. I measure a constant fluctuation which jumps anywhere between -50 to -175 (or so) somewhat like -50, -166, -75, -175, -80....continuous in fraction of seconds. NO screen change at any time, just black. Kudos to the brilliant people here!
It sounds like the controller for the Vscan voltage has become unstable or is not being supplied with enough voltage to maintain regulation. Unfortunately I am not in possession of this TV anymore so I am of limited help. Is there anyone here with a similar Vscan problem located near the Boston area? I wouldn't mind doing a house call to get to the bottom of this one. If so, message me via Instructables. Also, can anyone shed light on the mentions I've heard of certain problems being fixed by replacing some of the electrolytic capacitors? Which caps? What specifics problems has that solve? An unstable voltage regulator chip could be affected by not enough capacitance on the input or output. This is why I bring it up. Electrolytics do degrade over time.
Thanks for your reply mr12volt. In regards to the e-caps I can tell you that audibly (very faint) there appears to be some relationship to the fluctuation of the voltage...meaning that I can hear the cap altering buzzing with the voltage changes. I also found that if I press the input button on the remote I can hear the buzzing increase in volume (amplitude) until it defaults back to whatever input is active (after about 5-6 seconds) then back to the previous buzzing. These are the large case caps in pair closest to the Vscan circuit flow, before the test point.. I'm going to source new e-caps to change out although they appear to be in good shape visually. If I can find someone to check the e-caps I can further determine if that is my problem.
whitby905, Are you sure the buzzing is coming from the capacitors? It is more likely that the buzzing is actually coming from the transformers. The current pulsing through the transformers produces a changing magnetic field causing an alternating constriction in the coils of the transformer windings. The magneto-mechanical constriction and relaxation produces the buzzing sound, a useful diagnostic tool. One is able to audibly tell if there is some sort of intermittency in the transformer circuit by listening for these audible changes. My method of attack was to find the control IC (hint:look for the DIP parts) and poke its pins with my multimeter while listening for audible changes. This is VERY risky however (and slightly disconcerting when the buzzing jumps in volume or frequency). If your hand slips, the multimeter probe tips can short things out and cause more damage. I like to set the probes in position with the TV power off, then turn the power on and read the voltage off the meter. Less chance of disaster that way. Look up the datasheet for the control IC and compare the voltages you recorded for each pin to what they should be according to the datasheet. This takes a bit more advanced knowledge, however, feel free to post your results on this forum and we'll try to help. I wouldn't immediately suspect the electrolytics as the cause for any problems you are having unless there is some other evidence that points to their failure. Pressing the input button on most tv's causes some changes in the audible buzzing so I wouldn't necessarily label that as cause for concern or even unusual. It sounds like you're doing some excellent investigative work. Keep poking around. The more you play with it, the better chance you have of stumbling upon the solution. Keep us updated. p.s. Sorry for the late reply, I've been on holiday since July 7th.
mr12volt, Thanks for your reply and I hope you had a good holiday. It seems like this project is evolving or possibly devolving depending how you look at it. Upon further testing the voltages are ALL to spec...the earlier Vscan measurement may have been incorrect due to the pressure applied at the test point from the probe??? It is within spec and not jumping. I have found the data sheets for the IC's and am going to check values, but upon further investigation I've found that the controll board (directly behind the input board) there is 2 green LED's near top right of board that the left is on solid and the right is blinking. I don't know if that has any meaning or is an indication to my problem but I'm trying to find that out. Currently when powered on the set still gives the slight audible relay click and (your right) transformer buzzing, power indicator LED (blue) on, but no action from the pannel itself...nobody home. Any further thoughts?? I'll let you know about the IC check.

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