Help to identify fuse

Thread Starter

David Billington

Joined Oct 22, 2018
7
My LG washing machine PCB fuse has blown, I've identified the cause (faulty mains cable) and rectified it.
If I bypass the blown fuse everything now works. LG want ~ £130 for a new PCB
Unfortunately, the fuse is embedded in silicon potting compound and seems to be soldered into its end caps.
I've scrapped away the compound & smashed the glass in an effort to remove the endcaps and find the rating but I can't see the values and I'm afraid that if I'm not careful the endcap leg will snap at the board and I've got no hope of getting to the back of the PCB.
I'm not even sure if the fuse is mains or low voltage. Any help finding a suitable replacement would be appreciated.
 

MaxHeadRoom

Joined Jul 18, 2013
26,286
You can buy the fuses with solder type pig-tail ends already attached.
Cut it off the board, the details should be on the end caps.
Clean off the board and solder the new one in.
Max.
 

Hymie

Joined Mar 30, 2018
1,102
It appears that the pcb has been fixed within its housing, using epoxy resin (or similar), making repair of the board almost impossible.

As MaxHeadRoom says cut the fuse out, but as close to the fuse as possible, so that the fuse pigtails can be easily attached to the new fuse.
Try to use minimal heating during the solder operation – otherwise the heat might cause the fuse link to melt (after all it is heat from excessive current flow that causes the fuse to operate).

That construction is a bit naughty of LG – once the board goes faulty, they have a captive market for replacement parts.
 

ebp

Joined Feb 8, 2018
2,332
If you can't identify the rating from the endcaps, there are ways that a replacement can likely be chosen. Sometimes the secondary endcaps for the wire leads do obscure part of the markings.

Do you have a meter that will measure AC current and are you sufficiently experienced to be able to use it to measure current in a line voltage circuit safely? If you have a meter, can it measure RMS current or just average current?

I'm reasonably confident it is a line voltage fuse. There is clearly a switch mode power supply (the black thing with a bunch of stuff printed on the top is the transformer). I don't know what the other transformer-looking thing with the blue insulation tape is. It may be for noise filtering, but it is an unusual type for that. It may be for some sort of "standby" power supply (common if there is an always-on front panel or push-button startup like on a computer, rather than a switch that goes "clunk").

It might be helpful if you could post a photo of the whole board.
 

Thread Starter

David Billington

Joined Oct 22, 2018
7
Thanks for the suggestions folks, much appreciated, maybe LG won't get their £130 for bad design.
Unfortunately, my multimeter only does DC current.
The noise filter is on a separate board and the 'on' switch is momentary so the idea of a standby PSU seems logical.
I was hoping to avoid cutting off the end caps as the silicon gunk on the board will make soldering to the tail difficult.
However, if that's my best hope I'll try.
I've tried to find a bom or schematic for the board online but drew a blank.
 

pfofit

Joined Nov 29, 2006
57
The blue thing is an X capacitor. The board monitors and controls everything
These LG boards are a nightmare. 1/4" rubber/silicone/whatever on both sides of the board embedded in the plastic tray.
The stuff stinks just cutting into it. Pins on meter leads probing for issues and if you find a bad component, good luck getting to it.
You probably won't find diagrams for most appliance boards. Most factory manuals are block diagrams. No service, just replace. So sad. Throw away society. Even trying to salvage components is difficult cause of the stuff.

The main issue with these boards is the 3 phase motor controller under the big black heat sink. Either goes short or open.
That said, you said a line cord issue has been repaired.
Above advice of others is best, cut off the end caps as close as possible. The rating on these smaller fuses is under the end caps covering the fuse end caps. It is best to try a score a line and try to peel it back. Trying to pull them apart with pliers crushes them and can destroy the markings if they do not come apart easily . Trust me.
Use a scalpel to cut a square around the fuse leads into the gook( but not deep enough to score the traces and then scoop it out so you can solder a new fuse in. It dose not have to be as deep as the original. Hopefully there is not other issues.
Do not try to remove the board, you will destroy the casing and ruin the board. They have several thin traces right at the very edge of the board underneath and any prying will mangle them. There is smd stuff on the underside.

FYI: I have played with a couple of these dead boards to get them out for the fun of it and it was not fun. My best attempt was to score with a knife around the perimeter into the junk. digging out the stuff around the tabs in the plastic case that hold the board locked down. Cut one side of the tray on one side at each corner and fold down that side and apply a lot of hair dryer heat to the back. Then slide a putty knife or similar between the gook and bottom of the tray. There is little lines dimples and ridges on the trays bottom that interfere with sliding the knife
The stuff sticks like crazy to the board, is tedious to clean away to remove any components. Did I say that it stinks. I did this to get at the burnt motor controller part number.
 

Thread Starter

David Billington

Joined Oct 22, 2018
7
Firstly thank you all for such a warm welcome and generous help.
I've managed to remove and identify the fuse as a 250V 8A (no speed markings) so thanks for that.
However, given all your advice & the voltage of the fuse, I now think the line cord insulation break down is more likely to be a symptom rather than the cause of the problem, particularly as the insulation damage is before the blown fuse in the circuit. It looks like a short in the hidden motor controller, as pfofit suggested, is highly likely (I have to confess I didn't think to try running the main motor when I fired up the board). So it's time to admit defeat and get a new PCB.
 

pfofit

Joined Nov 29, 2006
57
Wow, you think a 8A fuse would blow before that melting occurred.
You can measure the output of the controller by measuring for resistance between the pins on the red connector to the left of it and next to the big black cap. Should be several meg between all 3 pin combinations. If I have the right connector.
Also measure the plug going to the motor. Should be the same resistance 3 ways. say 5-15 ohms

Not related to you but this morn i dug out one of my stinky boards from the garage to have a look see reminder.
It is different from yours but similar in design. I've had the board for at least 5 years. It's fuse is 12A time delay. printed on the board.
I've attached the pics for others to see the autopsy. I had dug into the stuff on the back in a few places to see what the chip numbers were, it was hard not to knock of smd resistors etc cause the stuff sticks real bad.
Also pulled the heat sinks.
cheers
IMG_2689.JPG
IMG_2691.JPG
 
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Thread Starter

David Billington

Joined Oct 22, 2018
7
Some heavy traces run from under the large heatsink to that red connector so it looks to be the right one, I'm getting ~900K ohms across all connectors (rising as I measure), no shorts. The motor windings are all registering 7.5 ohms, which is reassuring, although the motor is the one part that's still under warranty. The family is missing the washing machine so I've had to order a new PCB in the hope that it's the root cause. On the plus side, the new board has updated firmware which should solve a long-standing issue with the spin cycle failing to balance which drives the wife crazy :) Thanks also for the images, I've double checked for a fuse rating marked on my board but it looks like they've omitted it on the newer editions. Also, it smells like they've improved the potting compound as apart from the faint tang of rubber it's ok :)
 

pfofit

Joined Nov 29, 2006
57
Measurements sound fine, wonder where the melted wires come from.
The main plug should go to a line filter first and then to the board.
Was there any loose connections there.
Measure resistance at those connectors and each lead to ground to see if there are any shorts. Also investigate to see ifthe main cord or any other wires chaffed on a metal edge somewhere.
Do not try the motor/wash cycle unless you replace the fuse. It protects the board from vaporizing and the other components attached to the board..
Do you have a model # and did you find a hidden tech sheet anywhere in the unit. Shows a basic wiring bill and maybe diagnostics.

Some of the newer units have a heater / thermal well to maintain water temp. They need a heater cause the HE washers have nothing left to clean .
Less water, less agitation, less soapy water, the only factors left are time and temperature.
If you have a heater, I believe power goes thru a relay on the board (may have stuck contact) to the heater/heaters and has fuses at the thermal well.
Check those out for shorts
It's weird that a 8 amp fuse didn't protect that wiring cord. Makes me want to look elsewhere just in case.
From your diagram, could this nick be shorted somewhere or is it just melted from where it was touching something when it started heating up.
IMG_1010.jpg
 
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Thread Starter

David Billington

Joined Oct 22, 2018
7
The line filter shows no visible sign of damage, the connectors were all firmly clicked in place when first inspected. None of the filter connectors is reading a short to earth, the ring main has a 30mA RCD which didn't trip so I don't think a leak to earth is responsible. The cable run doesn't seem to offer much opportunity for abrasion or pinching but there may have been some prior damage, it's difficult to tell now that it's melted. The damage you highlighted is where a twist in the cable brought the 2 wires into close contact during the melt. The filter still seems to work as the PCB fired up when I jumpered the blown fuse. I've attached a shot of the filter with the new cable installed.
The washer is an LG F1443KD6 and I think the PCB is an EBR62175303, I haven't found any diagrams or info inside the unit.
The heating element has a resistance of 26 ohms which seems correct as it's marked as 2KW, can't see any external fuses for it.
I am concerned that I can't be sure of the cause of the cable overheat, I guess it's possible that not all of the current is drawn through that 8A fuse so there may have been a higher load at the cable although still not enough to blow the 13A fuse in the plug. The new PCB arrives tomorrow so I'll fit that and monitor the cable for any signs of overheat. Thanks again for the guidance it's appreciated.

 

pfofit

Joined Nov 29, 2006
57
Here is a generic lg washer diagram. It is not your model #, but might be similar enough to show you whats going on.
THey all do not have two heaters , the second one is a steam heater for "steam wash feature" labeled AG and comes with a valve and sensor . Also they all do not have a circulation motor. Measure the relay contact for the heater,the yellow one most likely, should be normally open.

2018-10-24_023706.jpg
 

Thread Starter

David Billington

Joined Oct 22, 2018
7
Thanks for the diagram, very useful. Looking at the wire & socket colours for my heater, they are an exact match for the diagram.
But both the yellow and black relay terminals read as open.
 

Thread Starter

David Billington

Joined Oct 22, 2018
7
New PCB fitted and washer powers up but claimed it was unable to lock the door. Door lock showed no sign of damage but I replaced it anyway and everything now appears to be working just fine. I keep checking the mains cable that had melted previously but so far it's not even getting warm. Thanks again for the help and apologies if this thread got a bit out of hand / off topic, I genuinely thought all I needed was to find the fuse rating.
 

MrChips

Joined Oct 2, 2009
27,686
Don't be too hard on yourself. The fuse is a safety mechanism to prevent further catastrophe such as burning down your house. A blown fuse is usually only a symptom to a bigger problem.

Glad to hear that your washer is back in operation.
 
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