LG TV wipeout

[loopyloo]

What do you think my chances are with this one ?

[mtv]

Lightning?

[ol' boy]

As a bit of a muppet with Electronics, i do like it when you can visually spot the fault

[Reschs]

Looks like the surge protector did its job.

Clean the area and replace the surge protector.
Check fuse and see how you go.

[loopyloo]

ha ha yeah I'd say lightning.
Fuse is blown and lost a leg.
Blue HV cap near the AC in lost a leg.
Another fuse just out of the photo is blown.
The little fuse in this photo is ok.
Not sure about the protector. Are they supposed to read open or short ? You can see I cut into the shrink around it to have a look and it looks fine otherwise.

Doesn't appear to be any other damage so I'd say it's worth spending a little time on it.

[tristen]

ha ha yeah I'd say lightning.
Fuse is blown and lost a leg.
Blue HV cap near the AC in lost a leg.
Another fuse just out of the photo is blown.
The little fuse in this photo is ok.
Not sure about the protector. Are they supposed to read open or short ? You can see I cut into the shrink around it to have a look and it looks fine otherwise.

Doesn't appear to be any other damage so I'd say it's worth spending a little time on it.

Go on, spend some time on it. I would.

As a very good friend used to say, "Look at this way. It'll keep you off the streets and out of the pubs".

Please keep us informed.

[bob_m_54]

If it was a lightning strike (and it does look like a power line strike), there is a possibility that there are other components throughout the TV that will be damaged. Quite often they will be visibly damaged as well. One TV I had that I had in for repairs, after a power pole strike, had the track right up to the earphone socket vaporised as well (a good illustration of why not to used a wired phone during a thunderstorm ) . And his VCR had many of the surface mount semiconductors blown completely off the board, with many little arc splatter marks around the board. This same customer had about half of his household electrical gear destroyed in the same event, including a couple more TVs and VCRs, Stereo system, fridge, spa and some other gear. The scary thing was, his power had gone off, and he was at the house fuse panel when the strike occured, which knocked him flat on his back.

But if you don't see any other visible damage, it's worth a shot, after replacing all the locally damaged its, including the varister. Did you check whether the bridge rectifier was damaged as well?

[loopyloo]

If it was a lightning strike (and it does look like a power line strike), there is a possibility that there are other components throughout the TV that will be damaged. Quite often they will be visibly damaged as well. One TV I had that I had in for repairs, after a power pole strike, had the track right up to the earphone socket vaporised as well (a good illustration of why not to used a wired phone during a thunderstorm ) . And his VCR had many of the surface mount semiconductors blown completely off the board, with many little arc splatter marks around the board. This same customer had about half of his household electrical gear destroyed in the same event, including a couple more TVs and VCRs, Stereo system, fridge, spa and some other gear. The scary thing was, his power had gone off, and he was at the house fuse panel when the strike occured, which knocked him flat on his back.

But if you don't see any other visible damage, it's worth a shot, after replacing all the locally damaged its, including the varister. Did you check whether the bridge rectifier was damaged as well?

The bridge rectifier is ok.
I think the varistor might be ok too.
It measures at 1.1 Mohms.
Does that sound right to you ?

[bob_m_54]

I would have expected higher, ie almost open circuit, but to be honest, I have never measured one to see what the resistance is. The thing is, they do degrade with surge operation. And for the 2 or 3 dollars they cost of a new one, I'd just change it anyway.

[loopyloo]

I would have expected higher, ie almost open circuit, but to be honest, I have never measured one to see what the resistance is. The thing is, they do degrade with surge operation. And for the 2 or 3 dollars they cost of a new one, I'd just change it anyway.

Mind you, that's measured in circuit. I'll take it out tomorrow and check.
Perhaps replacing it would be best, trouble is I don't know what to replace it with.
The marking on it are : INR 140621
I've tried google without success.

[Skepticist]

Jaycar stock several MOVs

Just going on the level of damage as an indicator of the impulse, everything on the primary side of that power supply is going to be a likely candidate for extreme damage. The MOSFETs, SMPS controller(s) and optoisolators being the most sensitive to extreme overvoltage so everything in that mains corner of the PCB will need to be thoroughly tested but the secondary side could have survived the spike unless the transformer(s) broke down between primary and secondary windings. Looks like the standby supply at the bottom of the pic that was closest to the blast but the amount of damage with leads blown off components indicates the impulse was not completely absorbed by the protection so might have reached much further than you'd expect based on a visual inspection.

Maybe consider removing some key primary side components and trying to power up the secondary side from another power supply to determine if the board is still healthy on that side before trying to repair the primary side - might not be worth the effort & expense.

[loopyloo]

Made a mistake on that varister.
It's number is 14D621. So looks like the 4500A from Jaycar will do.

Them ceramic fuses with pig tales are hard to get. RS has them if I buy 10 and wait 3 weeks. Might have to use glass ones.

[loopyloo]

Dunno why but I just had to try it after replacing the mains fuse, MOV and HV cap.
Applying power instantly turned the lights off in my shed. lol ... and of course took out that mains fuse again.
Just wanted to see what would happen. ha ha

The green line shows power flow.
I had to remove some parts then to confirm that all 4 FETs circled red are short.
Also, the bridge rectifiers are good.
Have to remove the opto's and test them with a little circuit.

(image is of the same board copied from the net)

P.S. Interesting !, I just noticed in this image that the board is marked 'L' and 'N' at the power socket, but it takes a figure 8 plug. (scratches head)

[tristen]

Place a 100W incandescent lamp in series with the mains supply to the unit and that should help to prevent a mains fuse blowing.

I used to have such a board made up incorporating a 240 VAC lamp holder, power cable with 3 pin mains plug attached (mains input) and 3 pin female socket (for output), the active of which is connected to mains active via the lamp. Use it to provide protection when connecting. I

[loopyloo]

Place a 100W incandescent lamp in series with the mains supply to the unit and that should help to prevent a mains fuse blowing.

I used to have such a board made up incorporating a 240 VAC lamp holder, power cable with 3 pin mains plug attached (mains input) and 3 pin female socket (for output), the active of which is connected to mains active via the lamp. Use it to provide protection when connecting. I

ah yer, it did knock out the circuit breaker in the meter box but the mains fuse I'm referring to here is the one on the board.

[bob_m_54]

Place a 100W incandescent lamp in series with the mains supply to the unit and that should help to prevent a mains fuse blowing.

I used to have such a board made up incorporating a 240 VAC lamp holder, power cable with 3 pin mains plug attached (mains input) and 3 pin female socket (for output), the active of which is connected to mains active via the lamp. Use it to provide protection when connecting. I

Yep, good tool to use when chasing these types of faults, except mine was a tad more rudimentary. I used old ceramic fuses that were open circuit and soldered leads to the end caps, on the top, to a light socket. then use the "test fuse" in place of the normal fuse.This is probably a bit dangerous though, and could killya if you touch the wrong bit.

If the power supply is cactus, the lamp shines brightly, if it's drawing normal current, the light globe glows dull.

[tristen]

The lamp will also help to protect the unit under test.

A power engineer acquaintance uses that method to test and fault-find switch-mode power supplies as they come off his production line.

It helps to protect PSU componentry when wiring faults etc. occur.

[loopyloo]

The lamp will also help to protect the unit under test.

A power engineer acquaintance uses that method to test and fault-find switch-mode power supplies as they come off his production line.

It helps to protect PSU componentry when wiring faults etc. occur.

Yes a lamp would do that and would be good under certain known conditions, but the only true guaranteed protection is for the meter box fuse. So for example if you were testing an appliance without an internal fuse or the appliance had a dead short, the mains would see the lamp as a normal load and not offer protection so the appliance would remain powered and may become hazardous. Especially if the item is non earthed.

I thought I should mention this because all sorts of people read these posts.

[bob_m_54]

Yes a lamp would do that and would be good under certain known conditions, but the only true guaranteed protection is for the meter box fuse. So for example if you were testing an appliance without an internal fuse or the appliance had a dead short, the mains would see the lamp as a normal load and not offer protection so the appliance would remain powered and may become hazardous. Especially if the item is non earthed.

I thought I should mention this because all sorts of people read these posts.

The "test globe" is used as a buffer for the equipment under test. If the equipment draws too much current, the light globe shines brightly, and is no different to powering a normal light globe from mains. In this situation, most of the voltage is across the light globe, with minimal current flowing, so the gear under test is protected. When Tristen was talking about putting the globe in series with the mains fuse, he was talking about the mains fuse in the equipment, not the Main power fuse in the fuse box.

[loopyloo]

The "test globe" is used as a buffer for the equipment under test. If the equipment draws too much current, the light globe shines brightly, and is no different to powering a normal light globe from mains. In this situation, most of the voltage is across the light globe, with minimal current flowing, so the gear under test is protected. When Tristen was talking about putting the globe in series with the mains fuse, he was talking about the mains fuse in the equipment, not the Main power fuse in the fuse box.

Yes I understood that. In his earlier post he described an extension lead he made up with the lamp in series with the active lead.
We used this method in a place I worked at many years ago for checking finished products on the factory floor. The lamps were built in to the tester. It was also a good way to get rough measurements such as millivolt drops, current draw etc. from the device under test. Sometimes a product would fry. That was mostly the older test equipment. When I started there, the move was to replace most of that equipment with PLC controlled solid state testers that had a high degree of measurement accuracy.

Frankly I never really though about using a lamp at home. I'll have to make one up.