electrolytic failures

[ex ttg]

Hi all
Years ago electrolytic failures on LT rails were something of a rarity.But now it seems that every lcd tv PSU more than 18 months old is littered with domed caps.Is this down to the proximity of the rear cover causing insufficient airflow or insufficient heatsinking again for rear cover manufacturing purposes?
With the crt tv's generally the high voltage caps(HT,200v rail etc) or SMPS start-up gave the problems.
Why now do we carry a bucket load of 1000uf 25v caps with us wherever we go?The caps we replace are invariably 105 c as well but LT caps way back were usually 85 c and happy.
Has anyone else given any thought to this?
Whatever the reason,here's hoping the manufacturers don't correct the problem.
Nick

[chammyman]

I know what you mean, I have changed caps on amps from the early 80's and only a couple were faulty, but a 2 year old pc motherboard all of them are bulging ready to pop.

I just thought price dictated the new stuff as rubbish, down to a price not up to a standard anymore.

Heat I don't think is a main issue as some of the stuff you see thats years old is under inche sof dust and they are fine but theres no coolign airflow.

[SUPER8]

GOD BLESS ALL MANUFACTURERS

[Turnip]

Hi Folks,

   Totally agree with all said, most succesful and profitable LCD Tv and monitor repairs seem to be in the P/S and invertor areas where high temperatures and ripple current provide income. Note that with computors stuffed with cooling fans, power supplies seem quite reliable. Lets hope Tv manufacturers don't cotton on.

    Incidentally, the local tip can be most useful for modern spares, only drawback seems to be Health and Safety concerns, preventing sites from being greener.

  Chris Steele

[broggsy]

my samsung lcd tv is a designers nightmare.The hottest parts are at the bottom and as the heat rises from this area it warms (ahem)  the electrolitics up as it journeys to the vents at the top of the back panel.
oh dear, as a retired r&d engineer this stinks as much as early motor car r &d engineers designing rust points so that cars didnt last that long (so i've been told). 

[Technomaniac]

Hi.  I think they are cramming too much into small spaces, they put hot components next to the caps, and the higher frequencies coming from the SMPS power supplies are harder on the caps as they have to charge and discharge many more times in a cycle. I'm glad someone is having more luck than I, just replacing the caps to solve the problems, I usually find myself replacing a bucketful of caps that are below par and the difference in performance isn't worth noting !  I have found my series resistance tester pretty handy, most times you can check the caps in circuit to get an idea whether they need replacing. Of course if the tops are bulging you needn't bother !  Regarding the 105 degree caps, I wouldn't use any other type, but, honestly, I don't think they survive any better than the 85 degree ones. And I'm on the tropic of Capricorn in Rockhampton, Australia, where it gets pretty hot ! Of course, in computer mother boards where you find a bunch of caps all in parallel, the series resistance cap tester isn't much use unless you remove the caps to check them individually. I've fitted a few computer fans into TVs and DVDs to slow down the failures over the years but you really need something to tell you when the fan fails and that's not so easy when time is getting away on the job. Sometimes you can fit a capacitor on the other side of the PC board to give better cooling.  But most of this gear is designed for snow country operation, I guess.

[tv john]

Hi guys, When I repair a lcd tv I offten remove  the screening can over the power supply, where possible. The cover in a 37" LG lcd that blows up can't be removed because it is used in conjunction with scart sockets and other inputs. What I do here is bend and fold back the top of this cover using a mash type hammer on a concrete slab, this helps air circulate better.                                                     The Maxim/Medion type power pcb with c330 runs hot as well.I offten screw an old tv heatsink to the existing one and touching the large wall mounting bracket if possible(to dissapate more heat).   

regards  tv john.

[Technomaniac]

Does removing screening cans cause extra radiation of RF energy within the cabinet and consequential earlier decomposition of plastic components such as the flaps on the ribbon cable connectors? Or am I the only one finding them more brittle than expected, after only a couple of years of service?
Its interesting that there seem to be comparable numbers of electrolytic failures in Britain, to the ones I experience in hot Central Queensland, Australia. I would have expected otherwise. I don't know whether they use real rubber for the capacitor seals anymore, I have noticed rubber belts and tyres used in electronics seem to have a different nature and shorter life. Seem to remember Tom Edison found he was able to make a rubber-like substance from Goldenrod, I think it was, during one of the world wars, when obtaining rubber from India to make tyres was a problem. Has anyone noted the ESR readings for the surface-mount electrolytics? They seem to be high. I wonder if inductance caused by rolling up the foils of an electrolytic has any bearing on the heat produced under high ripple? Is inductance cancelled by rolling the two foils together?