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Author Topic: 17" LCD Monitor Repaired.  (Read 1393 times)

tickmike

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17" LCD Monitor Repaired.
« on: January 21, 2012, 07:54:15 PM »

I was given a 17" LCD Monitor from 'Freecycle' the other day, the chap said the on/off power switch was faulty.
When I powered it up it came on straight away and then I tried the power switch, it seemed ok.
After using it for some while it went off and I could only get it on by pulling the mains plug out and in a few times  :hmm:  .
So I did a bit of a 'Google' search for that make and model and there were a few comments about blown capacitors, so after working out how you take the back off (cover comes off near base of stand and four screws to take off the stand then two screws to loosen the cover then carefully pries the cover seam open).
Looking at the main circuit board it was clear that a 1000mfd 16V capacitor had blown so I replaced it, tested it, then put it all together and It Works Perfect now  :thumbs: :dance:.

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asbokid

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Re: 17" LCD Monitor Repaired.
« Reply #1 on: January 21, 2012, 09:54:27 PM »

Top notch job!  Well done!
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HPsauce

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Re: 17" LCD Monitor Repaired.
« Reply #2 on: January 21, 2012, 10:21:25 PM »

Yes, I had one similar to that a while back.
It had a direct mains input and the problem was a mains-voltage capacitor in the PSU inside. Cost about 10p IIRC.

The other thing I'm getting quite good at is replacing the backlight inverters in laptop LCD screens that have died....  :graduate:
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roseway

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Re: 17" LCD Monitor Repaired.
« Reply #3 on: January 21, 2012, 10:35:47 PM »

Great job. :)  Electrolytic capacitors are probably the biggest weakness in electronic equipment, and if you've got the skill, it can be a cheap and fairly easy repair.
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sevenlayermuddle

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Re: 17" LCD Monitor Repaired.
« Reply #4 on: January 21, 2012, 11:26:41 PM »

That's good news Mike,

I know I seem to harp on about this, but whenever electrolytic capacitors repairs are mentioned I feel the need to stress that there's more to the specification than just capacitance and voltage.

All electrolytic capacitors are marked with a rated temperature, usually either 85 or 105 centigrade for consumer devices.  These temperatures may seem generous, and far beyond the temperature they will ever reach, but they are just a reference point for the manufacturers' rated life expectance.   Electrolytic cap's life expectancy is based on a fairly well-understood and predictable  chemical process and, as a rule of thumb, life expectancy doubles for every 10 degree reduction in temperature.

Manufacturers' stated life expectancy at rated temperature is often very short indeed, maybe just a month or two.   Thus it's important to use a capacitor with a temperature rating that very generously exceeds the temperature at which it will be used.  And the more generous you are, the longer it will last.  At most 'normal' operating temperatures a 105 degree capacitor should last about four times as long as an 85 degree capacitor, for example.

The other all-important parameter is ESR (equivalent series resistance).   When a capacitor passes any significant current the ESR leads to dissipation of power, in other words the device gets warm.  As described in the previous paragraph, that reduces life expectancy.  Quite apart from the temperature increase though, switch-mode PSUs often demand low ESR capacitors simply because they won't work properly without them.   So if you ever replace a cap' and it doesn't fix the problem, you may want to reconsider whether the ESR parameter of the replacement matched the original.

That said, well done Mike  :)

« Last Edit: January 22, 2012, 12:19:57 AM by sevenlayermuddle »
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tickmike

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Re: 17" LCD Monitor Repaired.
« Reply #5 on: January 22, 2012, 10:21:27 PM »

As I could not find my stock of new capacitors (Could not find them for all the other junk useful stuff in the roof  :'() I used one from a spare computer power supply and the capacitors temperature was 105c  ;)
I worked in electronics for a long time. :)
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I RECOMMEND TRYING / USING PCLinuxOS (www.pclinuxos.com) .
I have a set of 8 fixed IP's From my Eclipse isp.
BT ADSL2 line>HG612 set as a Modem, Bridge, WAN not Bound to LAN1 or 2 >Smoothwall (Hardware Firewall and routing) > Ethernet LAN, DMZ,WiFI LAN and Spare LAN .
DSLstats LAN2  linked Ethernet