EEVblog #347 - Bad Cap LCD Monitor Repair

[sonic]

Assuming the ESR doesn't match, can somebody explain to me in plain English the consequences of a mismatched ESR?

The whole point of these caps is to filter ripple current. If the equivalent series resistance (ESR) is too high or it can't cope with the ripple current, the ripple current won't vanish but instead heat up the cap, which will in turn increase the ESR - the start of a positve feedback loop. It will then either fail prematurely by vomiting its guts (the electrolyte) through the vent holes on the top or bottom or explode if the vent holes don't break after the internal pressure has increased enough. Either case might cause secondary damage.
So compare the ESR of your cap according to your datasheet to my measurements and replace it with a low ESR one if the ESR of your's is higher.
Out of convenience, and because I also wasn't completely sure about all these parameters, I bought a kit from LCDalternatives (also available via Amazon).

[T4P]

  I then saw some posts that says different sizes probably mean different ESR (whatever that is). 

Taller caps, skinny caps = Low ESR  Shorter, fatter caps = Normal

[Cranky]

I am currently using 2 LG Flatron L246WH 24" monitors I repaired in the same way.
They had 2 X 3300uF caps that had gone bad. Replaced with 3 X 2200uF (there was a spare spot on the board).
They are still going after about 18 months or so.

[TMM]

  I then saw some posts that says different sizes probably mean different ESR (whatever that is). 

Taller caps, skinny caps = Low ESR  Shorter, fatter caps = Normal

I can't say i have noticed that. If there is any 'rule of thumb' that is vaguely valid it would be that the physically larger the cap (regardless of aspect ratio), the lower the ESR. Even that doesn't always hold true. Panasonic FM series have very low ESR and they are fatter, shorter and smaller than most.

edit:holy thread dig batman.

[MrLostsoul]

I have a question. I don't have all the caps in hand. When I got the monitor, it didn't turn on at all. I replaced two caps I had already in hand. Now the led power lights come on the monitor. But after a few seconds, the power light goes off and when that happens, it makes a sizzle/zip sounds before the led turns off.

I think I just need to replace more caps. I would like to get your opinion. I have a Hanns-G HZ251HPB.

[John Heath]

I am writing to you on a Hannspree TV / computer monitor. You have my sympathy as you will not  find remote control codes for this puppy let alone a diagram. They appear to be a flash in the pan company that has disappeared into the abyss. Most of the time you can google the model # and someone will have had the problem and found a solution. Not with a Hannspree as there are too few of them out there.

The LEDs work for a while then stop , hmmm . I think your first guess is right for my 2 cents , more flat caps. As you have already looked your remaining flat caps do not have the classic bubble top. Step 2 use a ISR meter on the caps to see if you can sniff it out that way. And lets not forget any burnt looking resistors. 90 % of a LCD screen is low level electronics so it will seldom fail if not disturbed. This leaves only power supply issues of filter caps , resistors and such. Let it go for a while , sleep on it.  You get up in the morning and you know where the problem is. The mind has an odd way of sorting things out while we sleep.

[MrLostsoul]

Ok, I changed 2 caps. The led turns on then off then back on then off, and so forth. I'll check resisters too. Thank you - John Heath.

Does anyone have a recommendation on where to buy caps? I've used ebay in the past, and that's fine. But I'd be interested in a source/supplier who I can ask questions. If there a friendly vendor online somewhere?

[flumeboy]

Hi Dave - thanks for the video on re-capping these monitors

Question - when you encounter old capacitors that have leaked on your board, how do you recommend cleaning the board without damaging components? 

Cheers,

[vk3em]

For those like me who just watched the video and did a repair, please note that your capacitors may not visually look faulty.
In my Asus VW222U, I had no visual leaking or bulging of capacitors, but after replacing them, the monitor worked perfectly.
Unfortunately I was in a rush, so I ended up at Jaycar and the Samxon low ESR type, but if it gets me a few more years from this monitor (security cameras) I'll be happy for the $6 spent.