50PC1d power board

[caspermccormack]

Re: 50PC1d power board

I could only disconnect the bottom buffer to test the screen and the top half still had the fault while the bottom was blank.

[caspermccormack]

Re: 50PC1d power board

Checked over the top and bottom buffer boards and found a mosfet on each that has shown up different readings when checked on a diode test here is what I found with all fets removed from the board.

Black probe on the S, Red on the D = OL.
Black probe on the S, Red on the gate to charge it
Red back on the D =0.001, if i touch the G and D it shows up OL. again this is present on 4 of the 6 mosfets.

One shows 0.018 each way, and one keeps going up in value instead of staying at 0.001.

Going to change them out and see how I get on. Oh and the buffers test equally the same without the fets attached.

[tom66]

Re: 50PC1d power board

Checked over the top and bottom buffer boards and found a mosfet on each that has shown up different readings when checked on a diode test here is what I found with all fets removed from the board.

Black probe on the S, Red on the D = OL.
Black probe on the S, Red on the gate to charge it
Red back on the D =0.001, if i touch the G and D it shows up OL. again this is present on 4 of the 6 mosfets.

One shows 0.018 each way, and one keeps going up in value instead of staying at 0.001.

Going to change them out and see how I get on. Oh and the buffers test equally the same without the fets attached.

The 0.018 each way sounds like a shorted FET. Try with the gate shorted to ground, i.e. off. Also, you usually need a battery (3xAA or >=4.5V) to turn the fet on; the voltage produced by your meter might not be sufficient.

[caspermccormack]

Re: 50PC1d power board

Now that I have the 6 fets off the boards and I know one is shot may be the other 5 are weak. But heres the trouble, on the top buffer there is 3 mosfets (fairchild) G27 FQB46N15. The bottom buffer has 3 (fairchild) G26 FQB46N15.
So whats the difference with G26 and G27? same part number?

Called into my local Radionics and the nears they have is:

http://radionics.rs-online.com/web/p...633D4E4F4E4526

At that price I'd replace all 6, thats if they will work, any advice would be a great help.

cheers.

[tom66]

Re: 50PC1d power board

Now that I have the 6 fets off the boards and I know one is shot may be the other 5 are weak. But heres the trouble, on the top buffer there is 3 mosfets (fairchild) G27 FQB46N15. The bottom buffer has 3 (fairchild) G26 FQB46N15.
So whats the difference with G26 and G27? same part number?

Called into my local Radionics and the nears they have is:

http://radionics.rs-online.com/web/p...633D4E4F4E4526

At that price I'd replace all 6, thats if they will work, any advice would be a great help.

cheers.

Probably same part - different production lot code. Boards were made at a different time with slightly different parts. Wouldn't worry about it.

That MOSFET isn't SMD, the buffer FETs probably are. I think you need TO-263/D2PAK MOSFETs.

You will have a hard time replacing it without a hot air station too, but it may be possible with chip-quik. Never used that myself, though...

[caspermccormack]

Re: 50PC1d power board


These are the ones from the board.

[tom66]

Re: 50PC1d power board

These are the ones from the board.

Glad you were able to remove them; was it difficult? Here are some replacements on digikey: http://search.digikey.com/us/en/prod...PCT-ND/2441058

A bit more expensive, but you should only need one, as I suspect only one is shorted.

[caspermccormack]

Re: 50PC1d power board

Not to bad Tom, put on some solder and flux, held on the pad while applying pressure with a long nose pliers.

Do you think I should replace the lot, if they are in series and one is shorted will that weakin the others?

[caspermccormack]

Re: 50PC1d power board

Can i use the radionics parts if I solder the centre pin(drain) to the pad that the original fet was soldered to??

[tom66]

Re: 50PC1d power board

Can i use the radionics parts if I solder the centre pin(drain) to the pad that the original fet was soldered to??

Not really, as it wouldn't have adequate heatsinking and might overheat.

[tom66]

Re: 50PC1d power board

Do you think I should replace the lot, if they are in series and one is shorted will that weakin the others?

Whichever one is shorted needs replacement.

If they are in parallel you can do a quick hack: cut the source pin. There will now only be two FETs but it should work for 5 minutes. Don't use it for too long, as it may burn the other FET. This assumes they are in parallel - are they? Check this beforehand.

[caspermccormack]

Re: 50PC1d power board

Not really, as it wouldn't have adequate heatsinking and might overheat.

Thats what I taught!! I'll order from the post you had earlier.
I'd of scraped this project only for your help!!! cheers.

[caspermccormack]

Re: 50PC1d power board

Replaced the 6 fets on the buffer boards and tv started up like new, delighted with it, trimmed the voltages to spec on the board but the tv shuts off after 10 to 20 minutes with a loud pop, it will switch back on straight away and stay on for another 10 or 20 minutes??? I checked the temp on the service menu and it only got to 22.

[tom66]

Re: 50PC1d power board

Replaced the 6 fets on the buffer boards and tv started up like new, delighted with it, trimmed the voltages to spec on the board but the tv shuts off after 10 to 20 minutes with a loud pop, it will switch back on straight away and stay on for another 10 or 20 minutes??? I checked the temp on the service menu and it only got to 22.

AC detect okay?

[caspermccormack]

Re: 50PC1d power board

What do i look out for to check its ok?

[tom66]

Re: 50PC1d power board

What do i look out for to check its ok?

Check the voltage at ACD.

I have had the loud pop come from an LG 42PC1D when the PSU suddenly shuts down. It comes from the speakers.

[caspermccormack]

Re: 50PC1d power board

I'll take a look at the ac detect in the morning, Yeah loud pop from the speakers as it goes into standby. I am hoping i'm not to far from getting this tv back to working 100%. I have changed out the hybrid on the 42" and so far so good, not that bad to change it if you take your time.

Cheers Tom.

Casper.

[caspermccormack]

Re: 50PC1d power board

The Tv has being on all morning and afternoon and no faults???? Think I'll stick the back on and put it back on the wall, hope the f--k it's ok.

[tom66]

Re: 50PC1d power board

The Tv has being on all morning and afternoon and no faults???? Think I'll stick the back on and put it back on the wall, hope the f--k it's ok.

Rule 1 of troubleshooting: A problem that goes away by itself will come back by itself.

[caspermccormack]

Re: 50PC1d power board

The extension lead I was using during testing has a loose connection, its worked all day pluged into the wall.