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Monitor power board capacitor replacement


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5 replies to this topic

#1 OptimusSemi-Prime

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Posted 14 March 2016 - 08:03 PM

I have this monitor that will not get any power. it used to work until a power outage a few weeks ago. it had a nice image quality. it is an i-inc 28 inch (although it really measures to 27") with 1920 x 1200 res.

 

i would like to repair it. after research i kind of determined that i need to open it up and look for bulging or leaking capacitors on the power board, and put some effort into replacing the bad ones with a solder iron and lead-free solder. i can read about it all day long, but doing it is another story. 

 

two Qs:

 

has anyone ever disassembled another monitor looking for capacitors to use as replacements for the monitor they wished to repair?

 

  do the microFarads and voltages BOTH have to be an exact match?

 

thanks to all the readers and for the assistance !!!


Edited by hamluis, 15 March 2016 - 03:36 PM.
Moved from Internal to External Hardware - Hamluis.


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#2 Platypus

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Posted 14 March 2016 - 08:38 PM

The chances of finding the right capacitors in good condition in another monitor would probably be slim, and new capacitors aren't an expensive part. You may well find that another monitor may also have undesirable brands of capacitor like Elite or SamXon, even if they still appear OK. One thing that can be a problem is if your monitor does have bad capacitors, but they are an odd type. Samsung for example do have a habit of using odd sized capacitors that can be hard to find equivalents for, and if they're unusual, that generally means they need to be that size to fit in the space.

Capacity and voltage rating should be as close as feasible to the same. Sometimes odd values are used, such as 1200 uF, in which case 1000uF may be OK, since there's not close tolerance on electrolytic capacitor values, but slightly larger is probably better, or a mix giving the same total if the particular caps are simply connected in parallel. The voltage needs to be the same or higher, but a capacitor with a higher voltage rating may be physically larger and not fit. For example if there were 3 x 1000 uF 16V caps, and 25V ones would fit, that would be fine and they could last better as they will have a higher ripple rating. But you may well need to use 16V ones to have them fit in.

The capacitors used should be good quality ones with 105°C rating rather than the standard consumer 85°C.

Edited by Platypus, 14 March 2016 - 08:40 PM.

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#3 Havachat

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Posted 14 March 2016 - 09:23 PM

Replacing Bulging capacitors is an easy task , my 24" Samsung died about 18 mths ago , so i stripped it and found 2 of the 6 had bulges

.

Instead of replacing just 2 i replaced all 6 on that board while i was in there 

 

Samsung did use cheap ones initially so a trip to Jaycar Store and purchased 6 with same voltage , but uF was 1200 and not the original 1000.

 

As stated uF can be slighty higher , anyways installed the 6 and havent had any problems up to date.

 

Total Cost $ 15:00 and about an Hour to do.

 

Just take your time when doing so.



#4 OptimusSemi-Prime

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Posted 15 March 2016 - 06:22 PM

much gratitude for the tips and info. this is going to be a nice little project. in the end, i just couldn't stomach turning the monitor over to some technician service for repair then having the person tell me that i need to fork over a handsome chunk of change to get it back. that is the kind of thing  that can haunt your dreams.

 

  it is awesome that this site is a nice little corner of the web where people can ask about maintaining their computers.. sometimes i wonder if some of the membership here gets so good at keeping their systems maintained that there are still some pentium III computers with windows 95 or LINUX still operational on their desktops.



#5 Chris Cosgrove

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Posted 15 March 2016 - 08:44 PM

 

i need to fork over a handsome chunk of change

 

I fully sympathise and if you can get this one working again for the price of a few capacitors and a little sweat - well done !  In general monitors are not worth taking to a repair shop, the charges they have to make for labour tend to mean you are better off buying a new one.

 

I have to disagree with Platypus on one point where he says 'a higher voltage rating would be fine'. They will certainly work but electrolytic capacitors only achieve their rated capacitance at near to their rated voltage, at least that is what I was taught in electronics tech school. So, if the ones on the board, to quote his example, are rated at 16V then try and get 16V ones if possible. If you can't, then by all means use 25V ones. Do not use ones, in this example, with a rated voltage of less than 16V - their lives will be short.

 

Also, electrolytics are polarity conscious and marked with which terminal is +ve and/or -ve, as, normally, is their location on the circuit board. Make sure you put them in the correct way round or their service lives will be very short - like 10-20 mSec !  And noisy. And messy.

 

Chris Cosgrove


I am going to be away until about the 22nd October. Time on-line will be reduced and my internet access may be limited. PMs may not be replied to as quickly as normal !


#6 Platypus

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Posted 15 March 2016 - 09:58 PM

It's normal and, for broad tolerance circuits, not a problem for capacitors to vary in capacitance with differing DC bias voltage applied. It doesn't only happen with electrolytic capacitors either, here's a discussion of the effect in ceramic caps:

https://www.maximintegrated.com/en/app-notes/index.mvp/id/5527

For electrolytic capacitors, industry references suggest voltage de-rating of 30%-40%, conservative suggestions are up to 50%. What is best avoided is massive undervolting. A 100V rated electrolytic on a 5V rail may well have its life shortened by lack of chemical self-maintenance of the dielectric. The same reason can cause an old or long unused capacitor to explode when voltage is suddenly applied. The dielectric has deteriorated without the appropriate bias voltage present.

A 16V capacitor would typically be used on a 12V rail, with 25% de-rating. (That could be confirmed by measurement or reading labelling if present, but is fairly safe to assume since manufacturers cost analysis usually forces minimal de-rating.) A 25V part in that situation would be approx 50% de-rated, which is fine, and is likely to survive better in the application since for the same capacitor type, the 25V one can be expected to have a higher ripple rating.

Edited by Platypus, 15 March 2016 - 09:59 PM.

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