Help replacing a capacitor

[Carl DaBeast]

My PC monitor has recently started having issues turning on (status LED would blink and looked like it had issues "charging"). I suspected a capacitor had started malfunctioning so I decided to open it. Lo and behold I found a bloated capacitor, and it was the one closest to the DC input (which supports my suspicion).

 

I've decided to replace it and I found a capacitor that would arrive within a few business days instead of four weeks (thanks China...). The only thing about it is that the size of the capacitor is slightly smaller than the one in the monitor.

 

The capacitor in the monitor is also held down by some white silicon looking substance which is hardened.

 

Does the size of the capacitor matter ( ͡° ͜ʖ ͡°) if the rating is the same? What is the goop for? Is it only to hold the capacitor on place (and in that case can it be replaced with got glue) or is it for thermal reasons?

 

Thank you.

 

The capacitor I ordered.

The capacitor on the circuit board.

A better look at the goop.

[Windows7ge]

The white blob is more to keep it from moving around while in transit. So long as it's the same voltage and rating it should be fine. However I've been told there are good brand capacitors and bad brands. Which are good I'm not sure so I don't know if what you ordered will last a long time or not.

 

Also don't forget that they're polarity sensitive.

[Unimportant]

44 minutes ago, Carl DaBeast said:

Does the size of the capacitor matter ( ͡° ͜ʖ ͡°) if the rating is the same?

No, but there's more to it then simply voltage and capacitance rating. There's ripple current rating, ESR (parasitic resistance) and temperature rating, among others. This capacitor looks like it is part of a buck regulator circuit, judging from the inductor nearby (the part saying "220"). As such, the capacitor you ordered is probably not up to the task. It's a cheap 85°C capacitor that likely cannot handle the ripple current, has too much ESR and will likely fail again within a short period.

 

Something like the Panasonic FR series 105°C low ESR capacitors would be much more suited.

 

50 minutes ago, Carl DaBeast said:

What is the goop for?

To keep mechanical stress away from the solder joints. Solder joints are only meant to make a proper electrical connection, they should never be stressed mechanically. That capacitor is a somewhat larger and heavier part (relatively). It's weight would put mechanical stress on the solder joints, causing failure over time. The goop/glue provides mechanical support.

[mariushm]

You need a LOW ESR capacitor, a capacitor that is "optimized" for switching power supply circuits, which are the kind of power supplies used in modern electronic equipment.

 

The capacitor you chose is not suitable, it's only rated for 85c in the first place which tells me right away it's not of the LOW ESR variety. It may work right after you install it and the monitor may just be unstable (image go black and back to normal randomly, or monitor resets or turn off suddenly) but I suspect the capacitor will quickly go bad like the one you already have, within weeks of use.

 

You should also replace the smaller capacitor that's above the one that looks bad. That's also a LOW ESR type capacitor, and it's also used in a switching power supply circuit (a dc-dc converter circuit which converts something like... probably 12v .. 20v coming from monitor's power supply / the dc in jack to a lower voltage like 12v or 5v which is used by chips inside)

That electrolytic capacitor is too small, has too small amount of electrolyte (the substance inside which produces gas when it gets damaged) inside, so even though that capacitor could be bad, there's often just not enough gas generated inside to cause the top to bend or crack, it's just too small of a capacitor.  So you can't trust it's good just by the looks of it.

The two big chips to the right of the inductor (the piece with 220 written on it), the chip with a big arrow pointing to it and the one above it, seem to me like linear regulators. Those are there to convert a lower voltage like 5v to something like 3.3v or 2.5v. Those don't require low esr capacitors on the output, as they function differently than switching power supplies, but they do work at a high temperature, so often the manufacturers still use higher quality (and as side effect low esr) capacitors.

So I suspect that third capacitor (below the arrow) is there on the output of a linear regulator, so it's not "stressed" as much as the other two capacitors, so it's probably fine. But, if you do buy one or two capacitors you might as well order a third one as well, it would only add half a euro or something like that to price.

 

My advice would be to buy from Farnell or TME.eu , they're two European distributors of electronic components. It will be more expensive - I think the shipping costs are 5 euro or 5 dollars or something like that regardless how much you order - but you know for sure they're genuine parts and high quality and you get these in 3-4 days.

 

Farnell stocks Panasonic , Rubycon , United Chemi Con, Nichicon, and if you have no alternatives Wurth capacitors are also OK. Can't use just any series, it must be LOW ESR / Low Impedance series.

 

For Farnell Sweden here's a link with a bit of filtering pre-applied (only capacitors rated for 35v, 25v, 16v, 10v which is what you'll have in the monitor). You'll have to further sort by impedance (lowest is best) or by current ripple (higher current ripple the better)... but I'll suggest some series for you.

 

Link : farnell se long link with some filters preapplied

 

you want to look for panasonic  FM , FR  , united chemi con KZE , KY* (KYA , KYB may also work), Nichicon HM , HN, HW would also work ,  Rubycon ZL* (ZLJ, ZLH, ZLQ,), YXF,YXG 

 

TME.eu probably sells to Sweden, they stock some of the "tier-2" brands, not the most expensive "Japanese" capacitors but still with good reputation. For example they also stock Samxon capacitors which are decent, and if you have no alternatives there's also Elite or Aishi (these are used a lot in led lamps and stuff like that and they survive)

 

Here's link with same pre-filtering applied:   link tme.eu low esr capacitors

 

same applies, don't buy the cheapest from the list, not all series are suitable. If in doubt, Panasonic FM and FR are great choices, but you may have to order minimum 5.

 

Note that you can use capacitors rated for higher voltage, so your 470uF 25v capacitor could be replaced by a 470uF 35v capacitor if it's cheaper or you can buy it in quantity of 1 instead of minimum 5 for example, just keep in mind the dimensions (diameter and height), because you'll want to be able to close the monitor back panel.

Capacitance value should remain the same, it's important. If you have no choice, you may go up a step ("steps" are usually 10-20% jumps up and down) , for example instead of 470uF, you may successfully use a 560uF capacitor.

 

ps. The white goop, they explained well. It's there just to keep the capacitor in place, to prevent vibrations, flapping about during shipping to stores, to reduce stress on the leads... it's not critical, you can just use a small tip screwdriver to carefully remove it from the board. 

 

[EsaT]

What's external PSU's output voltage?

Depending on output voltage of power supply 25V might be "tightly" sized.

Especially if used power supply is some cheap so and so regulated.

 

And you need to check that diameter/how big capacitor can be fitted there there.

 

Having good voltage endurance margin is always good for capacitor life.

Also usually notch bigger capacitance is completely safe and in filter capacitor use would get stressed less, especially if original sizing was tight.

(usually lower ESR and higher ripple current rated)

 

 

Also with one clearly failing capacitor some of the others might be worn and they're unlikely to be any better quality ones.

Usually swapping every capacitor doesn't cost much when you start it, especially compared to shipping costs and tiem anwyway spent.

Small capacitance low voltage capacitors simply don't cost much any compared to that.

 

 

I guess that other PCB is for backlight power source and it has at least one capacitor.

 

 

8 hours ago, mariushm said:

For example they also stock Samxon capacitors which are decent

Decent enough to have two out of three bulged in backlight's power supply feeding rail in neighbour's 1600x1200 20" LG monitor...

While they shouldn't have had any business of doing that considering at most medium level usage.

If I hadn't sold him my old (of course recapped) 25.5" 1920x1200 LG to replace it, he might have well gotten monitor problems soon.

After recapping that 20" LG went to my father to replace 17 year old Nokia 449Xi CRT.

[mariushm]

1 hour ago, EsaT said:

Decent enough to have two out of three bulged in backlight's power supply feeding rail in neighbour's 1600x1200 20" LG monitor...

While they shouldn't have had any business of doing that considering at most medium level usage.

If I hadn't sold him my old (of course recapped) 25.5" 1920x1200 LG to replace it, he might have well gotten monitor problems soon.

After recapping that 20" LG went to my father to replace 17 year old Nokia 449Xi CRT.

Yes, I agree with you that back then (when 18.5 .. 21" monitors were common) the manufacturers used crappy capacitors from less reputable brands like Samwha, Capxon, Elite, Su'scon (or whatever) or Samxon ... they used low esr capacitors from series that were borderline suitable for the purpose. Capxon was the worst offender imho.

(I actually suspect they also did it on purpose in a sense, since the capacitors used were just good enough for a monitor to last maybe a bit more than around 3 years if monitor is used for 8-12 hours a day or something like that, when warranties for monitors are normally for 1-3 years)

 

The capacitors Samxon makes now are series with better chemical composition, with better quality, you won't buy today the same series of capacitors from Samxon or Samwha or others that were used back then.  And as for polymers, Samxon sells them under the X-con brand, and they're just as good or better than brands like Apaq for example (used by Asus and others a lot)

 

So if you know what to buy Samxon or Teapo or Taicon are safe choices, these are considered sort of 2nd tier, after Japanese capacitors. I would dare to say even Aishi and Elite would be ok if you really know their limitations, or even Jamicon capacitors if used for general purpose, nothing low esr. 

 

[EsaT]

4 minutes ago, mariushm said:

Yes, I agree with you that back then (when 18.5 .. 21" monitors were common) the manufacturers used crappy capacitors from less reputable brands like Samwha, Capxon, Elite, Su'scon (or whatever) or Samxon ... they used low esr capacitors from series that were borderline suitable for the purpose.

Those were supposedly better Samxon GFs and neither they were attached to any hot parts, like Samsung has done.

Though don't know if they were little undersized.

IIRC upped all three to higher capacitance from Panasonic FR/Rubycon ZLH etcs from Digikey.

That 25.5" model with guaranteedly lot more usage again had IIRC Samyoung NXBs in power supply and some Samwhas in logic board.

 

One of them got couple 130C rated Rubycon RX30s to some miscellanoues duty, because Digikey didn't have anything else above generic level in stock with those values.

Plastic frame of monitor might rot before those...

[Carl DaBeast]

Thanks for the replies. It sucks that I jumped the gun on ordering the part but I'll look at this as a learning experience. It will still be several times cheaper than buying an entirely new monitor, and now I'll have spare capacitors for something else!