Author Topic: Replacing capacitors  (Read 1884 times)

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Offline Mutinyguy

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Replacing capacitors
« on: December 19, 2016, 07:07:20 pm »
Never picked up a soldering iron before until a few days ago...I purchased a Weller station and a few practice soldering kits from Amazon...was fun to do :)
This was all practice for replacing 5 capacitors on my wife's Samsung 204b monitor. I found a good utube video and ordered the capacitors.
I went to work on the board and had a heck of a time desoldering the bad capacitors...3/5 were leaking...seems like I had to turn up the heat on the iron to get it to melt the solder on the board and with the wick made a bit of a mess...anyway I was able to replace all of the capacitors and got everything back together...turned it on and everything looked good!!
Until the next day when my wife was complaining the screen was flickering....hmmmm....it got worse over the next few days. She did not have that problem before I replaced the capacitors...the monitor needed many toggles on the on/off button for it to come on but no flicker once it did power up.
So I took it apart and visually looked at the capacitors and they look fine...so not sure where to go from here?
I see on ebay there are used "tested" boards for this unit so will probably just buy one of those...but I am a bit disappointed that my first repair did not work :(

Thanks for any input...

Jim
 

Offline stj

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Re: Replacing capacitors
« Reply #1 on: December 19, 2016, 07:20:27 pm »
2 rules.
1: dont buy caps on ebay, most are fakes - use a real parts store like digikey.
2: buy the right series for a psu - i use Panasonic FR series.

and dont solder any in the wrong way around  :o
 
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Offline Mutinyguy

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Re: Replacing capacitors
« Reply #2 on: December 19, 2016, 07:24:00 pm »
2 rules.
1: dont buy caps on ebay, most are fakes - use a real parts store like digikey.
2: buy the right series for a psu - i use Panasonic FR series.

and dont solder any in the wrong way around  :o

Purchased the caps in a kit from ccl-la.com and not sure what "psu" stand for?
Yes I made sure the negative lead went to negative on the board  :-+

Thanks for you input :)

Jim
 

Offline grevan

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Re: Replacing capacitors
« Reply #3 on: December 19, 2016, 07:24:19 pm »
That´s what i was going to say,
pay attention to the capacitors positive and negative sides.
PSU stands for Power Supply Unit.
« Last Edit: December 19, 2016, 07:26:29 pm by grevan »
 
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Offline Seekonk

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Re: Replacing capacitors
« Reply #4 on: December 19, 2016, 07:35:37 pm »
Was it a double side board?  The trouble you had soldering may have damaged the plated through holes.  The symptoms are like the output cap is open or not connected.
 
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Offline Mutinyguy

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Re: Replacing capacitors
« Reply #5 on: December 19, 2016, 08:40:45 pm »
Was it a double side board?  The trouble you had soldering may have damaged the plated through holes.  The symptoms are like the output cap is open or not connected.

Sorry showing my ignorance here...It looks like this:
http://www.ebay.com/itm/Repair-Kit-Samsung-204B-Combo-Kit-LCD-Monitor-Caps/330584668610?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D38530%26meid%3D05f2fa6060c9423780853495548f9f29%26pid%3D100005%26rk%3D4%26rkt%3D6%26sd%3D330499791302

Jim
 

Offline Gyro

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Re: Replacing capacitors
« Reply #6 on: December 19, 2016, 08:50:47 pm »
Is it the backlight that is flickering? If so, make sure you have plugged in the tube connectors firmly. There are also a lot of surface mount components on the back of the board. Visually check that you haven't accidentally disturbed the soldering of any as you desoldered the capacitors.
Chris

"Victor Meldrew, the Crimson Avenger!"
 

Offline DimitriP

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Re: Replacing capacitors
« Reply #7 on: December 20, 2016, 05:42:19 am »
Was it a double side board?  The trouble you had soldering may have damaged the plated through holes.  The symptoms are like the output cap is open or not connected.

Sorry showing my ignorance here...It looks like this:
http://www.ebay.com/itm/Repair-Kit-Samsung-204B-Combo-Kit-LCD-Monitor-Caps/330584668610?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D38530%26meid%3D05f2fa6060c9423780853495548f9f29%26pid%3D100005%26rk%3D4%26rkt%3D6%26sd%3D330499791302

Jim
Is this the actual seller of the capacitors you used?
   If three 100  Ohm resistors are connected in parallel, and in series with a 200 Ohm resistor, how many resistors do you have? 
 

Offline Paul Moir

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Re: Replacing capacitors
« Reply #8 on: December 20, 2016, 06:14:06 am »
Quote
seems like I had to turn up the heat on the iron

While the amount of copper on the printed circuit board traces can affect your soldering iron temperature, my bet is the difference you noticed was going from leaded to lead free solder.  To wick that horrible stuff up, I first add leaded solder to the joint, then wick it up using extra flux added to the wick.  Actually, I always use wick with my own flux:  I have never gotten good results without doing this despite using name brand wicks.
 

Offline Mutinyguy

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Re: Replacing capacitors
« Reply #9 on: December 20, 2016, 11:22:04 am »
 

Offline Mutinyguy

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Re: Replacing capacitors
« Reply #10 on: December 20, 2016, 11:23:41 am »
Quote
seems like I had to turn up the heat on the iron

While the amount of copper on the printed circuit board traces can affect your soldering iron temperature, my bet is the difference you noticed was going from leaded to lead free solder.  To wick that horrible stuff up, I first add leaded solder to the joint, then wick it up using extra flux added to the wick.  Actually, I always use wick with my own flux:  I have never gotten good results without doing this despite using name brand wicks.

OK that makes sense...what is the "best" type of flux to purchase? I have seen flux pen's...is that a good way to go?

Thanks!

Jim
 

Offline Paul Moir

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Re: Replacing capacitors
« Reply #11 on: December 20, 2016, 07:30:15 pm »
Personally I kind of like the paste fluxes.  Lately MG Chemicals 8431 which comes in a syringe.  Up till lately it was their liquid rosin flux but it's a little harder to clean up and while very sticky, it doesn't have the stay-put-ed-ness you get with the paste.
But it's all about personal preference and availability.  I'm sure there are many that work just as well if not better.

My favourite tool for cleaning up is one of those cheap "acid" brushes with the bristles cut very short along with isopropyl (rubbing) alcohol.
 
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