EEVblog #347 - Bad Cap LCD Monitor Repair

hi if you saw my dumpster-diving video you know that I scored two of these Samsung sync master 204 B monitors with the nice tip portrait are tilting stand on them excellent ah and I assumed they would work because I have got monitors from down there before that have worked no problems at all but unfortunately these are - don't look like they work at all the light doesn't come on I've tried to hook them up to a PC nothing usually you should get some sort of menu or something like that so it looks like these things are cactus and of course in all these sort of things about pretty much upmost electronics are gear like consumers and computers and set-top boxes and all sorts of things I think I've done a video on that before one of the most common culprits of course is the electrolytic capacitors in them they fail bad and I had a whole bunch of comments on my dumpster-diving video that these samsung sync masters are notorious for bad for having bad quality caps in them so I thought we'd open it up and try and replace the caps in it and see if it fixes the problem Oh check them out first and see if that's the issue probably I reckon with about 90% 95% certainty maybe um it will be the caps in the power supply because electronics is pretty reliable are just regular active and passive components very reliable reliable but electrolytic capacitors of course have a dielectric liquid in there that can actually dry out with use and when they get hot and these things get reasonably hot inside and I've done videos on this before so almost certainly it's got to be the caps let's crack it open and I can't see any screws on this thing I think it's a plastic retaining Clips around the edge what a bastard spud your time well that was pretty annoying and now you got a it just looks like it just lifts out now I would have preferred screws hate those plastic retaining clips we've got a there we go back panel just lifts off real easy this thing is quite heavy it's a really well shielded as you can see it's a brill built like the proverbial brick outhouse I like it it looks like this front panel connector just comes off the switch front panel switches and bingo we have our screen we can now open this sucker up we should only have to get into this top access panel here and that should give us access to the power supply circuitry under there I've lost my good phillips screwdriver unfortunately so i'm going back to the old one i've had since i was a kid i had that since before I even turned 10 I think that's how long I've had that screwdriver so let's have a look two screws there doesn't sound right what's going on here that's all integrated with this it's folded this is all folded over the top and integrates with aa it's rather annoying ah ah there we go all right cut the screws on the side and then this whole top bracket should just lift off here we go yep beautiful and as you can see there's not much to this thing just the two main boards here and instantly I mean all we care about is the power supply one over here I mean we've got some backlight inverter stuff here this is the mains power supply section and why we've got it straight away and look they're dodgy caps on brand can you believe that Samsung use caps on that one actually looks okay there's no bulge in it but these are also caps on brand up here which I'll give you a look at and these are dodgy look you can I don't even have to measure those you can see the bulges in them and the choice of those caps is quite surprising because this isn't otherwise very nicely engineered and laid out you know at mains switch mode power supply they're doing all the right things here except for the choice of caps it's actually very nicely laid out and they're doing all the right stuff here they've got two trans orbs they've got semester there are silastic in those over so that they don't vibrate loose the main DC input filter cap is silastic down ah all happening they've even got the dip marker to show how it which direction the board flows through the dip soldering machine you know the wave soldering machine and ah lovely and here we go we have some caps on 25 volt 330 micro farad you can see the bulge in the top of the cap near the vent hole there and that's a dead giveaway that there's been pressure built up inside there which means that all the electrolyte fluid has dried up and of course this one has actually vented out check it out that's an 820 micro farad ATS you don't see 820 micro farad too much these days you know usually it would be like an even thousand but there you go I'm 820 micro farad 25 volt caps on absolute classic case of electrolytic capacitor rupture there it's gone bad I don't even need to get out my Bob Parker ESR meter and measure those I know they gone bad any time you see a bulge in an electrolytic capacitor like that you know it's gone and you've got to replace it and we've also got some caps on 330 Mike 25 volt ones on this side here and that one has a slight bold unit to the one behind it seems to be okay but as a matter of course I'm going to replace all of these caps on brand caps now I'm not sure if I'm actually going to replace that main DC input filter cap the mains input filter that's 100 micro farad for 50 volt because I can't see any signs of bulging in that at all but it is a caps on brand so it instantly you know brings into question even if I didn't know what brand it was if you see that the same brand are all leaking and bulging over here you've got to assume that you're going to have a similar problem with this one but I reckon I can probably fix this thing by just replacing the DC output caps because these are the main output caps on the main DC rails which power all of your electronics here and of course if they no good if the all of the electrolyte fluid in there is dried up all the pressures built up in there then of course you're not going to get a nice smooth DC rail to power electronics you're going to get tons of ripple on there and all your digital electronics is just going to play silly buggers and not going to work at all so yeah I don't know whether it depends on how much they cost and whether or not I can get them from J cart now because I want to fix this one like now in the next hour so or both of these monitors so I reckon I could probably get away with not replacing that one it's not great for the long term but anyway for the short term fix I reckon just the output ones and if you're interested in seeing the mainboard here it is it's got a date code on there of 2007 but looks of it but it's pretty much just a single chip solution as you'd expect these days you know here's your input connector your DVI and your VGA it's all in one chip geez I can remember monitors I can remember working on flat-screen monitor designs back in 1994 I think it was about 94 ish and to do what they're doing inside this monitor even at lower resolutions like 800 by 600 at the time this is before widescreen really kicked in was hideously complex in it required um you know a board full of chips just to digitize the VGA input and convert it to flat screen now it's just ah one little QFP package thank you very much you can see the RF ferrite bead there for EMI suppression so that will knock some of the edge off those digital signals high-speed digital signal strong flowing through that parallel datalink there and of course there are some surface mount electrolytic caps on this logic board but really you know I don't think they're going to be a problem at all it's definitely the ones on the main power supply board you can see on the back of the board here they've got some insulation actually very nicely clipped into the main board I really like that Samsung have really gone to work quite a bit bit of effort to design a thing properly which is all the more disappointing why they're using crap quality caps in this thing check out the bottom of the board here with it's a nice sexy black solder mask on green it really does look very nice I really like it they've engineered this thing quite well as I said look at the high-voltage isolation slots they've routed into all this stuff a signs put a bit of pride into this at layout let me tell you it's beautiful and we've talked about this before in other videos you can see the selective removal of the solder mask on those traces as they thin down see how they're fatter here and they thin down here and just to increase the current capability of those traces just a tad and they've done the same thing down here on the main this is the mains input switch here the IAC connected with the main switch and they've done same thing there so after a quick trip to JK I picked up some dubious a brand low ESR capacitors here I say that because J cart don't exactly have a stellar reputation for supplying prime spec quality parts it's like whatever they can get really and these are si brand never heard of them I don't know don't trust them as far as I can throw him but it's the only choice I had for one to do this properly I would have gone too far Nels much further ordered them I can't wait I wanted to fix it within the hour so these are the best that I could do for 70 micro farad 25 volt replacing the 330 micro farad's if you're going to replace these don't go down in capacitance value if anything go up they didn't have any 330s so I'm using 470 25 volt they're a bit physically bigger but they are 105 degrees C raided that's what you want because the life of capacitors drops with an increase in temperature and if you've only got 85 degree C rated ones they're not really good enough and it's a low ESR type that's what you want with switch mode power supplies like these you don't want regular capacitors low ESR trust me that's the business so I picked up that and I picked up a once again si brand thousand Mike 25 volt once again low ESR are physically quite a bit larger I think it's the same map in pitch here a bit now beggars can't be choosers it's all they had you know if I went too far Nels yeah I could have picked up just exactly the right cap that I wanted in the slim profile and you know a quality reputable brand sourced from the you know there are no one reputable supplier but anyway well throw these in it'll get it up and running as long as they physically fit let's give it a go so they have it every place start five caps here these ones are as you can see they weren't physically the same diameter they are a little bit wider in the diameter so they don't quite fit in there that well but anyway good enough it's going to work I am didn't bother to replace the mains input cap because they were like 750 each at Jake our screw that but these ones only cost me you know a dollar or two total so hopefully that will get us up and running alright let's power this thing up and see if she works here we go hey the LED you probably can't see that but the LED is consistently on and it's working look to that and log digital no problem does menu work so there it is check signal cable that is working a treat I'll put the front panel clip that back on Endor no worries I'm sure if we hook that up to the VGA output of the notebook or the DVI output it'll work a treat beauty and here's inside the second identical monitor the main input filter cap looks fine once again the same caps on brand these ones look okay but I've kind of change them as a matter of course and there we have the bowl G's lar one and the second monitor I've replaced all the caps in there lights coming on and and bingo there it is fixed as well no worries whatsoever ha and there it is works perfectly both of them so they have it two repaired Samsung sync master 204 B 20 inch monitors I got from the dumpster good old dumpster dive in fantastic fixed within 10 minutes work and a couple of bucks worth of caps and these are excellent monitors beauty and there's probably some poor design engineer at Samsung right now just doing a big facepalm because they designed and built this thing beautifully only to have some decade in the purchasing department purchased dodgy caps instead of probably the Panasonic ones they specified in the bill of materials purchasing just rom and we'll get those cheapest caps we can we're going to make a million of these Mondas aha look I save the company you know fifty thousand bucks in capacitors beauty her not and just remember when you're fixing our bad caps like this to replace them with good quality low ESR types the Louis R is important because it's the high ESR that causes the internal heating and then the pressure buildup and the drying up of the electrolyte inside the capacitor that causes all these problems in the first place so they're a bit self-perpetuating in that respect if they start out you know a little bit dodgy then they're going to heat up a little bit inside that extra heating increases the temperature inside the cap increases the ESR equivalent series resistance which then increases the heat even more dries out more of the electrolyte and so on and so on and it just snowballs until what just spews expand stops working at all like we saw in these monitors and lots of stuff lots of consumer items PCs and set-top boxes and DVD players and TVs a lot of them will be an easy fix like this by just changing the caps in them and if you liked the video please give it a big thumbs up that helps a lot and if you want to discuss it jump on over to the eevblog forum catch you next time

Channel: EEVblog

Views: 449,403

Rating: 4.9417963 out of 5

Keywords: dumpster diving, samsung, syncmaster, lcd, monitor, repair, bad, caps, capacitor, leaky, low, esr, replacement, switchmode, switching, power, supply, 204e, teardown

Id: Ytw57212X2o

Length: 17min 38sec (1058 seconds)

Published: Fri Sep 07 2012