Author Topic: LG Side by Side  (Read 3155 times)

Offline ApplianceGuru

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Re: LG Side by Side
« Reply #10 on: March 29, 2012, 02:10:44 PM »
A fuse should never blow. . . period.  A fuse is a safety device that blows FIRST before a more expensive component blows.  Something failed, and caused the fuse to blow.

The fuses that are soldered in are fuses that let you know there has been a failure in the relay system.  If that fuse blows, then it means more relays were closed than were supposed to be closed.  In some cases, this can feed voltage to parts of the circuit that shouldn't be getting voltage at the specific time.

Basically, if the fuse is soldered in, and it is blown, replacing it will probably result in another blown fuse.
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Offline Ol' Lonely

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Re: LG Side by Side
« Reply #11 on: March 29, 2012, 02:45:27 PM »
Are you guys talking about the fuse on this board?

Main Control Board Part # 6871JB1410D


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Offline PARTech

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Re: LG Side by Side
« Reply #12 on: March 29, 2012, 03:22:59 PM »
Or you can see several right after a power outage from the spike when they cut it back on..... Notorious up here with the power companies. :)
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Offline haroldsappliance

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Re: LG Side by Side
« Reply #13 on: March 29, 2012, 05:03:23 PM »
Never had a call back on this fuse replacement.

Offline ApplianceGuru

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Re: LG Side by Side
« Reply #14 on: March 29, 2012, 07:02:40 PM »
I had a big long explanation for how and why a fuse should not blow, even in voltage spike situations, but when I hit "Post" ApplianceJunk took too long to respond and I lost it all!

In short, the varactor should short any voltage spikes to neutral, saving all the other components on the board from being exposed to anything over 120V AC (RMS).  The fuses are also protected.

The LG refrigerator board has a varactor, and two fuses.  The fuse that is soldered blows during board failure.  If the replaceable fuse blows due to voltage spike, this means the voltage protection circuit on the board is failing, and you should replace the board.  This also means some components were briefly exposed to a higher voltage, which has weakened them.

A varactor can absorb high voltage spikes, but each spike reduces it's ability to absorb future spikes.  If a fuse is blowing due to voltage spikes, then it means the board is failing.

The only way to know if a voltage spike has occurred is to look at past voltage data, which nobody has access to.  If a serious voltage spike has occurred, then you will always see a blown varactor.  This means the rest of the board is fried also.

There is a reason the manufacturers tell you to replace the board if the soldered fuse blows.  I know they never explain why, and it is probably because they want you to buy the whole board from them, instead of replacing board components.  My guess is they encourage buying the whole board because too often you can spend weeks trying to narrow down the root of circuit board failures, and it takes some pricey equipment to capture the failure.  (digital analyzers, oscilloscopes, data loggers, etc....)

I used to work on flight simulators, and we had test equipment that got up to tens of thousands of dollars per piece.  A few years after I left, the company spent $70,000 on a top of the line digital analyzer.  This can be justified when you are working on hundreds of flight simulators worth a few million each, but in the appliance world. . . . . . . not even on a $25,000 AGA range.
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Offline AJ

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Re: LG Side by Side
« Reply #15 on: March 29, 2012, 08:01:17 PM »
Quote
I had a big long explanation for how and why a fuse should not blow, even in voltage spike situations, but when I hit "Post" ApplianceJunk took too long to respond and I lost it all!


Sorry about that. We have been having some issues with our new host/server that I have been trying to get resolved today.


Thanks for posting.
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Offline PARTech

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Re: LG Side by Side
« Reply #16 on: March 30, 2012, 06:22:21 PM »
With two LG boards (and one GE) that I am looking at the line in goes straight to the (soldered in place) fuse not to a varactor.  Seems that would indicate a problem more with the logic on the board or a power supply problem.
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Offline ApplianceGuru

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Re: LG Side by Side
« Reply #17 on: March 30, 2012, 10:05:41 PM »
You are right.  I stand corrected.

On the LG board, the replaceable fuse is not protected by the varactor.  The line voltage goes through the fuse, and then straight to the varactor.  So if the varactor draws a lot of current from a spike, it will blow.  Of course, if the varactor drew that much current, it has most likely been weakened, although I don't know of any way to see how much the varactor has been ruined.

The fuse is rated in amps, and the varactor is rated in power.  A higher voltage at a fixed amperage will result in more power being dissipated by the varactor.  ( Voltage x Current = Power )  A 1 amp fuse blowing at a 1,000 voltage spike would put 1,000 watts across the varactor for split second.

I suppose by designing the circuit this way, when a severe voltage spike happens, you might get a blown fuse, which tells you the varactor has been weakened, and is no longer dependable.
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Offline ApplianceGuru

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Re: LG Side by Side
« Reply #18 on: March 30, 2012, 10:24:43 PM »
Basically, if it's your fridge, and you are a DIY'er, put in a fuse, and see what happens.  Of course, now that the voltage spike protection circuit has been weakened, the next spike might not get dissipated, and it could damage board components the second time around.

If you are a professional, replace the board, because you have no real way of knowing what damage has happened, and paying customers really hate dealing with the hassle of call-backs.

American power line voltages are so well regulated, most of us only experience one or two serious household voltage spikes in or lifetime.  The fact you don't get call-backs within your warranty time has a lot do do with reliable American power.

If this appliance was in Mexico, it wouldn't last a year!  (yes, I have seen this happen many times)  Down there people put UPS power supplies, and surge protectors on expensive electronics.
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Offline tgoods

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Re: LG Side by Side
« Reply #19 on: March 31, 2012, 09:00:04 AM »
I installed a fuse holder and fuse on an LG in Sept 2010,  http://appliancejunk.com/forums/index.php?topic=6741.msg30366#msg30366. It's still working.  The service manual even says to replace the fuse if blown even though is not meant to be replaceable.  Fuses and circuit breakers trip for no reason all the time.  It's called nuisance tripping.  I do agree that if want to ensure no callbacks, replace the board.

 

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