Mulja tv repair portal
Equipment Repairs => LCD TV forum => Topic started by: scooby-doo on August 23, 2011,05:09:00
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Hi
Just a couple of questions regarding capacitors
Most of you know that capacitors are a common fault, I just want to understand a couple of things
Why is it ok to replace 25v caps with 35v caps?
uf Rating...how much movement have you got on the uf rating, for example lets say I have a 1200uf cap could I replace this with a 1000uf capacitor or a 2000uf cap, or do you need what it says on the tin?
And do capacitors solely fail, is there another component on the board somewhere that is starting to overload the capacitor for it to fail?
Thanks for any advice on this one, have looked at Wiki but I am Lee Layman and get lost in translation.
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hi
its best to use same value cap's but the higher voltage
is ok
dave
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Hi,
Agree with Sparky. Electrolytic caps usually fail because of internal heating causing them to either dry up or swell - either causes a rise in impedance and more heating.
Reason for failure is high ripple current in power supplies of low'ish secondary voltages but high current.
Must admit I try to use the biggest low ESR cap that will fit the board - Chris.
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Cheers Sparky
So why didnt the manufacturer fit 35v instead of 25v is this a cost issue, and if the manufacturer did fit 35v in the first place would this of prolonged the life of the TV.
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hi
prob they wont tv to fail
dave
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Hi
I think it is a question of cost, with price erosion causing falling TV prices every year they have to save money, and this can sometimes cause premature failure of components when they get it wrong
Brian
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Right OK, I am a little bit with you Sparky, in the fast moving industry of electronics and progression why would any company in the right mind want a tv to last as long as my Grans CRT, it would put you lot out of jobs.
Moving onto the uf I know you have a 20% tolerance, but is it more important to stick bang on what comes out of the set or do some of you throw caution to the wind and lets say fit a 1500uf where a 1200uf has been.
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Hi,
Gran's tv probably had a 150v HT line (if a modern ancestor - failing that some 250v plus for some older gals)
Ripple current was much lower so rarely a problem.
As to capacitance value of replacement - as big as will fit the board at voltage of original - stand to be corrected but don't think increased working voltage generally equals lower ESR.
Final thought - without those dodgy caps some of us in the trade would be awful slim - Chris.
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As a general rule yes, its ok to use higher voltage caps as long as they physically fit (if they’re next to a heatsink your asking for problems)
Try to stick to the same values unless you have a good reason not to, it can cause problems further down the line with the repair or the set in later life.
With the repair of PSU’s I’d try to use 105degs caps, even if 85degs are fitted, some manufacturers use 85 and these can give problems, I’d also go for ones around 2000-3000 hours span if you want a bit of life on the repair.
Most caps engineers see are swollen (top or bottom) due to the electrolyte turning from a liquid to gas, cheaper caps tend to be more prone to this and as the caps that give problems tend to be the same ones in the same boards no matter what the brand used is then it does lead you to think that it’s a number of reasons that cases the fault
if you want to read some more info. on failing caps you could try the badcaps forum, although after reading you might think that capacitors are gettign the blame for everything from failing sets to why mars bars aren't as big as they used to be ( and don't even get me started on the size of a packet of Monster Munch)
regards
Andy
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Hi Andy,
Can you justify your second paragraph ?
(Try to stick to the same values unless you have a good reason not to, it can cause problems further down the line with the repair or the set in later life.)
Just curious - Chris
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I have noticed that we didn't get the problems with capacitors when the snickers bar was called 'Marathon'
They changed the name to Snickers and all of sudden we are flooded with Samsung TV's with bulging capacitors!
Coincedence? I think not!!
Brian
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Brian, you might have a point there.
my point about the correct values, I should say the correct capacitance, although you can use a higher rated capacitor in most cases (and the set will work and sets will work with low capacitors before they give up) I have found that if you use caps that are a lot higher in value (if we’re talking about electrolytics) then its more of a practical consideration, they’re more expensive and often to large although as I’ve said you can in most cases get away with it.
With the case of a 820uf being a slightly odd value engineers will often sub a 1000uf taking time to wedge it under the heatsink or stuffing them out of the top. If a customer sees it then you can expect a good ear bashing, its not great practise, so I'd say yes, "try" to stick to the correct value.
regards
Andy
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Brian
Did you.get the email I sent?
Andy
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Hi Andy
I emailed your email address on this site, so it looks like you didnt get my email and I'm not getting yours!!
Regarding the capacitor debate, I always fit the exact capactance value, but regarding the voltage I try to make sure the working voltage is not dramatically higher than the original or this can effect the ESR
ie fit a 16v in place of a 10v but don't go sticking a 250v one in!!
And I didnt realise anyone was still using 85 degree caps!!
Brian
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Brian,
Look in a vestel psu next time you have one. Sites will often sell lots of caps in a "bulk buy" at a cheap price and you'll find they're often 85degs
Yes, a degree of common sence is needed with caps. you can upset how a cct. works by changing the cap values although size probably prevents you from doing this.
Ye, I got your email and replied to it, you should have 4 emails from me (try looking in your trash).
I'll resend from a different email account
regards
Andy
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Hi Andy
I have recieved just one email from you and nothing in trash
Brian
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Hi Brian,
Guess you're right - substituting a well known name for another is hell for the over 70s.
I used to love Imps, Waggon wheels and that chewy woody stuff before realising years later my jolly memories were a bit suspect.
Still feel that big caps are good (sounds a bit Animal Farm) - Chris
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Back in the middle ages when I was a boy and most things were either valve or solid state cap values were " near as damit does " as long as the working voltage was equal to or + up to 15 % of the original.
Laterly with the ever increasing use of high frequency applications such as in SMPS's the boffins at Manufacturers courses all seem to sing from the same hymn sheet... exact same replacement, voltage temp tolerance and capacitance.
I questioned the wisdom of this at a sony course and was told with the increasing use of feedback loops, opto sensors and error detection circuits the slightly increased charge/ discharge time of a higher voltage same capacitance replacement can cause instability in a PSU.
I can't vouch for the validity of this explanation but it is a possibility....that said I've often substituted higher voltage caps and never noticed it causing a problem...
I suppose the final nail in the coffin is the fact that all manufacturers insist you do not alter or modify any part of the circuit or component specification without express authorisation of teh designers in order to maintain operational and safety parameters so from that point of view I guess its like for like.....
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The main reason/ excuse for not changing the value of a capacitor would be explained by the phrase “by changing the value of any component you change the characteristic of the circuit “
Although this is true as is “do not alter or modify any part of the circuit or component specification without express authorisation” you could argue that capacitors should not spew forth after 12 months.It would also call into question the practise of using equivalent or uprated parts. I can think of one psu supplied by a major supermarket that had a knock of smoothing capacitor in that a different value than that shown on its canister.
When subbing caps its wise to try to stick to the original values and types, uprating the voltage is a good idea as is using slightly better quality caps. I’m sure if manufacturers had tested all the sets for 12 months before launch most of the problems would be cleared up, its also worth pointing out the number of “stock faults” on a particular set compared to the amount of components fitted in the set.
Regards
Andy
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Hi folks,
Guess it's all health, safety and clip-boards - even when we as a country are going down the pan -
Bit too old to hold with that - puff - Chris.
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I'm afraid old duffers like me an lots others will continue to do what we have for years suck it and see ! if it works it can't be far off being right !
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Hi folks
Guess if some old duffers are still lose and mending - rule of thumb applies 'till New/New Socialists re-house us for our own safety next election, and chuck the key.
Curiously, I'm a Socialist - just don't have the clip-board or pension - born too late, and still working - Chris
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If an engineer is repairing sets with a high success rate, then its always wise to keep on with what you do.
An electronic circuit is often made up of smaller circuits designed for a particular part.
If you look at the attached datasheet for use with an ic commonly used in sets most engineers will of worked on, it gives recommended values for the components and these are then used in the circuits, they’re not just doubled in size and a larger voltage used, its only after repeated use do common faults appear.
As modern devices are often designed to do the work of several parts, they’re designed to save on extra parts and space and therefore lowering the cost. A major reason for capacitors failing is heat, adding a larger sized part might increase temperature and cause problems with the part of the circuit its used in.
This why when we’re designing kits and repairing sets we use the correct value and sized parts.
That make sence?
regards
Andy
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Hi Andy,
Sense ? - well not really, your third para is a problem - if replacing a capacitor with lower initial ESR than the original (selected initially mainly for economy with a limited service life in mind) Heat generated by new cap's reduced ESR will be less and reliabilty obviously greater.
Only go on about it as have chased reliabilty for a lot of years and am still in business - for some possibly good reason.
I make no observations on your kits, one way or the other, but would be happy to give 'em a go should I need to - Chris.
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Just browsing through the various posts and this is possibly worth a mention, we have hot air guns, stereoscopes, digital meters, pattern generators etc, our workshops, i thought, were adequate, but if you can, buy an E.S.R. meter. Ours arrived yesterday, eighty pounds + VAT/p&p. Paid for itself already in PSU repairs, its worth every penny.
Tony Walker
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Hi Tony,
Got one of those Aussie ones years ago, loaned it to a chap in the trade and never got it back.
Saved enough eventually to buy a 'Peak' ESR60 (extending the leads as those fitted were so short they drove me nuts)
Guess without our duff 'Caps' most of us would be serving fries down at the roundabout - Chris.