EEVblog #347 - Bad Cap LCD Monitor Repair

[IanJ]

The Samsung and Thomson boxes are rubbish and have bad cap issues.

The older (and possibly newer) Amstrad boxes are very well built. I took one apart - full of Rubycons!

I have one of the very original boxes when SKY HD first came out (Thomson box I presume)...........still going strong after all these years. Have always meant to get around to opening it up and seeing what brand caps it has.
PS. It's either ON or on STANDBY 24/7.

Ian.

[tom66]

The Samsung and Thomson boxes are rubbish and have bad cap issues.

The older (and possibly newer) Amstrad boxes are very well built. I took one apart - full of Rubycons!

I have one of the very original boxes when SKY HD first came out (Thomson box I presume)...........still going strong after all these years. Have always meant to get around to opening it up and seeing what brand caps it has.
PS. It's either ON or on STANDBY 24/7.

Ian.

I have a spare Thomson skydigibox (not HD, or sky+) which has two bad caps. It has worked with them for at least 6 months but has some problems tuning into certain channels. I have got to get around to replacing them but we're using the HD box now.

[cheepokleebo]

The rule is simple: Google the product - the chances of someone having the exact same problem as you are high.  Case in point - the second monitor having the leaky cap in the exact same position. Fixed my Philips DVD player in 15 minutes - one bulging 1000uF was replaced by 2 470uF caps and a gob of silicone bathtub sealer to hold them in place (very ugly). Three years later it still works.

[madires]

That's why I always keep a good stack of low ESR caps (common values) of well known vendors in the drawer ;-)

[SeanB]

RS SSM in many cases is 5, so i do tend to have some always, or i will nick them off a scrap board for a quick check. Helps before ordering to see if it in dying has not taken other parts with it as a farewell gesture.

[mzacharias]

As a repair tech I can attest that the high ESR causes regulation problems, forcing the output voltage higher, til the caps vent. Some PSU's have a zener diode across one or more output filter caps so the zener will short first and protect components downstream. Generally this forces the entire switcher to shut down, but sometimes the switching device will also die.

The power supply unit in these Samsung's is a vendor part Samsung gets from someone else. Their home LCD TV's have has many problems in this area. Samsung has signed consent decrees to repair these at no cost even several years after the warranty expiration. A good portion of my income comes from these jobs.

[FenderBender]

The main filter cap is rarely faulty.  Almost always the only issue is the low voltage side.

I think that that cap is the PFC correction cap, which don't encounter too much stress..which isn't to say that it couldn't go bad, but it's less likely. The output caps are subject to a lot of high frequency ripple, so sure those of course matter.


Yeah I was curious why you (Dave) needed to have it up and working so quickly, but it makes sense now. Electronex!

As you've said, those monitors are probably otherwise very good. Might be worth to recap them with good Japanese caps if you get the chance. If you don't think you'll need them, you can probably get $50 out of them at least.

[David_AVD]

The main filter cap is rarely faulty.  Almost always the only issue is the low voltage side.

I think that that cap is the PFC correction cap, which don't encounter too much stress..which isn't to say that it couldn't go bad, but it's less likely. The output caps are subject to a lot of high frequency ripple, so sure those of course matter.

No, I was referring to the reservoir capacitor which is has the rectified mains (340VDC) on it.

[T4P]

Pretty much most companies that we know not be to "reliable" or any consumer product NOT from japan will have CapXon caps ... still work better than some taiwanese caps from the P4 days i think?

[TriodeTiger]

Or the other perspective - build them to run until the next line comes out, or the cycle when businesses tend to order new updated PCs. Why not have the monitors go too?

I had a syncmaster once, a 24 inch CRT meant for medical work if I recall - they designed 'em well back then - and businesses would keep them if they didn't take up half a desk and leave a permanent depression in them.

[Rerouter]

well to add to the drone, today i had to go and replace one of the main filter caps in my modem, though it was branded ST, though oddly enough the ones of the same make that lived near the sodding hot processor where still in fine nick (really need an esr meter)

for reference to anyone else, it was a SS4200 modem and was the 6.3V 1000uF cap, the rail its on sees spikes near 7V rather commonly, seems they thought they would group 2 caps rather than buy a seperate higher voltage one, or pay for 2 higher voltage ones, 

[SeanB]

The 24 inch Syncmaster CRT units had a very well known failure mode, the line output transformer would die, either quietly short or spectacularly explosively, at around the 5 year mark, just out of warranty. Had one pop exactly 1 week after the warranty expired, to the day. The transformer is not available as a spare part ( discontinued 3 years before with the end of the range) so it was tossed. The way the agents did warranty claims in the last 2 years was to give you a new monitor of the same or bigger size if not available, they did not have the spares any more to fix them.

[G7PSK]

The First time I ever experienced catastrophic electrolytic failure was on an answer phone in the 1981, It exploded with such force that it displaced the bridge rectifier and voltage regulator, there was no switch mode on that machine just a mains transformer, but it was not even running of the mains as this machine was in a remote farm where there was no mains so the unit had been rigged to run from 24 volt battery when the generators were turned off, as it was I was sitting with my back to the machine when it exploded, I repaired the machine and a couple of years later it did the same thing again, The capacitor was 35 volt rated if I remember correctly the second time it happened  I replaced with a 60 volt cap and it never went again, but the first time it blew it sounded like a shotgun being fired right behind me.

[Ed.Kloonk]

...but the first time it blew it sounded like a shotgun being fired right behind me.

How do you know what that sounds like?

[notsob]

Ask his father in law

[FenderBender]

I think that that cap is the PFC correction cap, which don't encounter too much stress..which isn't to say that it couldn't go bad, but it's less likely. The output caps are subject to a lot of high frequency ripple, so sure those of course matter.

An active PFC cap sees a lot of stress the low frequency AC rms current and the high frequency AC rms current. Then it’s also discharged from the downstream converter.

The main filter cap in standard input filter has a larger surface area to radiate heat. They are subject to the 2fline AC rms current for charging and the High frequency switching ripple for discharging. Capacitor impedance decreases with frequency which is why when you look at ripple current specs a cap that can handle 1Arms at 120Hz may be rated for 1.4Arms at 100kHz.

http://www-s.ti.com/sc/techlit/slup060.pdf

Acer also uses or at least used those capXcon capacitors.I've replaced them from those monitors as well.

Alright then, my mistake.

Oh darn, I have an Acer monitor...I've had it since 2007...Fingers crossed...

[T4P]

I hope yours doesn't blow up like one of my Samsung monitors did, the fuse popped so hard and there were sparks!
Turns out the transformer shorted out!

[Slobodan]

I have replaced electrolytic caps in ATX power supply few months ago with Jamicon brand. Are they any good?

[T4P]

I have replaced electrolytic caps in ATX power supply few months ago with Jamicon brand. Are they any good?

NA brand, but not really any good.

[Slobodan]

I have replaced electrolytic caps in ATX power supply few months ago with Jamicon brand. Are they any good?

NA brand, but not really any good.

If you could just tell me what does "NA" stands for?

[mariush]

Probably North America.

Jamicon is OK for general purpose capacitors... like remote controls, toy cars, radios, CRT TVs..  but not for places that heat up a lot like back of lcd monitors or for circuits that require low ESR due to high switching frequencies.

They're not Low ESR, can't handle as much ripple as the Japanese caps...  and overal their technical specifications don't match those of Japanese brands.

So probably not, I don't think they'd last long in a power supply. But it depends on how much air flow you have there, how sensitive your pc components are to ripple and other things.

[Slobodan]

Thanks. I remember that I chose those beause they were the same specs (or a little bit better) as the ones I replaced. They are 105 C and 1.1 Arms ripple current rated. The power suply is "DTK Computers" brand, and as far as I remember, the "original" caps (output filter caps) were some chinese brand and not even "low esr".

Edit: "Original" capacitors are Fuhjyyu TNR. Jamicon is better than them, isn't it?

[FenderBender]

Well anything is better than Fuhjyyu. I still would not trust Jamicon in any medium to high stress environment. Honestly, the price difference between a Japanese brand and something like Jamicon is so small, just get the Japanese brand. Sure they probably don't sell them at the local electronics store, but it's usually worth it to wait 2-3 days for Farnell, Digikey, or Mouser to ship you a few.

[Slobodan]

Thanks. I will order better quality capacitors from Farnell then.

[Slobodan]

Well what can I do, I was curious, so I couldn't help it... I have opened my SAMSUNG SyncMaster 920N (it had 6700 working hours) and I have found that all electrolytic caps where fine (at least not bulged), and they are Samxon GF(M). So my question, again, is are these caps any good and should I replace them with good quality ones, as a precaution?

http://www.lckdanny.com/samxon/