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. 1There’s some great photos online of other plagued PCBs.

isometric view

Also known as “leaky cap” or “capacitor plague.” 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. 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.

Wikipedia

, 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 2These part numbers are Digikey stock part numbers., 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!

 

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

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Comments

7 responses to “Samsung LCD monitor repair”

  1. Jinshin Avatar

    Dear Sir,

    Hi I am Jinshin, I represent my company, Mohotec- which has more than 300 items in stock of A grade, brand new LCD panels supplier to share our sincerity of cooperating with you. Mohotec is one of the biggest suppliers in Taiwan.
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    Jinshin
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    1. Rob Avatar

      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. […] then I opened up the box and discovered a ton of capacitor rot. Cool, I thought, I’ve got experience with this!  The hardest thing about the job would be getting adequate clearance to the components for both […]

  3. Vj Avatar
    Vj

    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. Rob Avatar

      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.

  4. yogakakiFei Avatar

    Hi, my Samsung LCD card’s F301 already blown. I cannot find the part here, can I just direct short the circuit? Is it safe to do this?

    1. Rob Avatar

      Well, you could short the fuse but the board could smoke later.

      I listed the part numbers in the post. You can find them on Digi-Key.

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