Samsung LCD monitor repair

A while back, a guy contacted me through my blog about contracting some monitor repair. He had come to acquire a bunch of LCD monitors that all had failed in similar fashion. So I took him up on his offer to repair them so he (and I) could resell them all.

The monitors were mostly all Samsung 740N. I did some early research and found this forum that went into great detail about the problem and how to fix it.

As it turns out, Samsung made a bit of a bad design decision in its component selection.  A few aluminum electrolytic capacitors, all 820uF, were especially prone to “puffy cap” syndrome, shortening their life operation {1}.

isometric view

Also known as “leaky cap” or “capacitor plague” {2}, it’s a disease that can render your personal electronic gadget inoperable.  The only cure was capacitor transplant.  Also typically affected was a poly fuse that was blow open-circuit.  The designators in question are:

  • C111
  • C112
  • C301
  • F301

The suggested part numbers {3}, as per the above mentioned forum, are:

ItemPart NumberDescriptionPrice
C111, C112, C301P11221-NDFUSE PICO FAST 3A 125V AXIAL$0.61
F3010251003.MXLCAP 820UF 25V ELECT FC RADIAL$1.07

It should be noted that the above capacitor replacement turned out to be slightly too tall.  There was mechanical interference with the monitor’s plastic case (not good!), so I found a better, shorter-bodied cap.  That part number is P14423-ND.

I replaced the caps and now the monitor(s) works great!

new poly fusefinal assembly & test

 

Full Project Gallery:

Don’t forget to contact me if you too need some electronics repair work done!

Footnotes:

  1. There’s some great photos online of other plagued PCBs. []
  2. Wiki of course has a great article on the syndrome. To quote:

    As an electrolytic capacitor ages, its capacitance usually decreases and its equivalent series resistance (ESR) usually increases. The capacitance may abnormally degrade to as low as 4% of the original value, as opposed to an expected 50% capacity degradation over the normal life span of the component.[11] When this happens, the capacitors no longer adequately serve their purpose of filtering the direct current voltages on the motherboard, and system instability results. Capacitors with high ESR can make power supplies malfunction, sometimes causing further circuit damage.

    []

  3. These part numbers are Digikey stock part numbers. []

7 Replies to “Samsung LCD monitor repair”

  1. Dear Sir,

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    1. Hi, Jinshin. Though it might appear otherwise, I’m not a design firm. I’m just a dude with a soldering iron. And time enough to spare on adequate documentation.

  2. Hi I just replaced all 3blown caps and the pico fuse but still there is no display,its the same Samsung 740n monitor any suggestions or help thanks

    1. Hmm, bummer. Yeah, I’ve got some of my displays that were still dead after doing the fix. On some of those, I suspect that the power supplies were bad too.

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