Panasonic Plasma power supply transformer

[AdamOfAus]

Hi guys,

I think this power supply is faulty, should this transformer be missing a big hunk of magnet as per photo?

How would I go about finding out a suitable replacement? Can't find any numbers on the part itself.

When the tv gets power a switch on this board clicks on and then off and a red led blinks 4 times.

Any help appreciated.

[AdamOfAus]

Found this number on it.

ga 3 sb42aj29

No results on google, hmmm

[capt bullshot]

These transformers are custom made for this board. You won't find anything.
My advice would be: Find a scrap board with a transformer of the same mechanical core size, scavenge the core from that to replace the broken one. Heating the transformer (using a hair dryer or heat gun) should help with removing the core. Be aware there might be something else defective on your board apart from the broken transformer core.

[sean0118]

Yes it looks broken and is might be custom made. 

Although, the ferrite bobbin (the broken bit) is probably a standard size so you should be able to buy one and slid it on. I'm not sure what this type of bobbin is called, maybe EE?

You could also try taping on the broken bit if you can find it. 


I'm guessing it might not be the only issue, give the board a good check over and check for shorted transistors etc (with the tv unplugged).

[AdamOfAus]

Thanks gentlemen.

Yeah I've had a good look at the board and have done a little diagnosis with other boards disconnected from this board.

Oh well, do rs online sell magnets that might be suitable?

I haven't found bits of magnet in the tv, just small pieces. Catastrophic failure perhaps.

[sean0118]

Yep RS do sell them, just try to find one that is the same size / shape. There are different types of ferrite, but hopefully it will be close enough.

https://au.rs-online.com/web/c/power-supplies-transformers/transformers/transformer-ferrite-cores/

Digikey's search might be better, you could find a part number on there and see if RS sells it too:

https://www.digikey.com.au/products/en/magnetics-transformer-inductor-components/ferrite-cores/936?k=transformer


Also you might not need to desolder the transformer, just remove the old ferrite bobbin as capt bullshot suggested and glue the new on on.

[AdamOfAus]

Yeah If it was just that magnet it would be a pretty sweet fix. Guess I'll measure it up.

[AdamOfAus]

Have measured it up and found a match.

There are 2 version with different AL Ratings.

314nh vs 525nh

Any guesses on which would be suitable?

[sean0118]

I'm not sure, they seem pretty close to each other, I would go with the cheapest. 

[AdamOfAus]

Lol okay. And to remove this magnet you just heat it up? What glue would be good for this application?

[sean0118]

hmm I'm not sure what is used, maybe electronics silicon? Any glue is probably good enough. Maybe tape it on first just to check if it works.

[AdamOfAus]

Roger, cheers fella and others.

[T3sl4co1l]

Wow... it... yeeted itself the hell out of there? I don't even know how that would fail that way! Like, buildup of pressure making a cannon?

Which... if it did fail that way, it could only be from electrical failure inside the winding, generating smoke and gas.  I don't think windings are usually tight enough to hold onto that kind of pressure, it should just simmer and smoke and short out.  In which case obviously, you have much more to worry about.  (But this is particularly unlikely if no fuses or transistors have died -- have these been checked?)

Anyway, that's going to be some kind of resonant supply (possibly for the high voltages needed for the panel?).  The inductance will be important.  The way they set that, is by cutting the center leg of the core a little short, leaving an airgap in the middle.  That's what your two purchase options are.  And... without the missing suspect, you have no way to tell what it was originally.  So, that's just great, huh?

Ah well, if it works it works (but do listen for ticking or squealing, and check if it's getting too hot, or if the voltages aren't right), and if not, you're out a TV anyway.

Tim

[wraper]

IMHO should be simply mechanical damage. As already said, the easiest and with the best and safest result would be to find the missing bit and glue in back. And yeah, ferrite core is not a magnet  .

[Gyro]

Agreed, finding the broken bits, even if multiple, and gluing them back together (cyanoacrylate) would be the preferred option. If it is a flyback converter then the inner limb will be gapped and simply buying a replacement core would not preserve this.

[AdamOfAus]

Hmmm, interesting.

Yeah I can't find any bits at all really. Maybe I should just a buy a good used power supply.

Oh well. Thanks

[m3vuv]

once had a woman who went nuclear like that!

[AdamOfAus]

Lol, yeah women can go that way sometimes.

Just an update, I did find the rest of the magnet and glued it in. Same thing happening unfortunately. Switch on the board clicks on, then clicks off. I've had a good look at the board, capacitors, etc. and can't see any problems. Need some new batteries for my multimeter.

Ah well, it continues.

[perieanuo]

hi
find another ferrite like that you glued (the glue won't repair the ferrite by the way, the current won't flow in that ferrite core) and 'clone' the transformer if you got time.not easy but doable, you just need the copper wire with same diameter and the paint for electrical isolation (sorry I don't know the word for this type of paint ).
usually when I repaired tv's I got easily equivalent for almost any smps transformer in china, even those for neon tubes for backlight in plasma, just a little googling for chassis name of that TV or whatever power supply he has.
regards,pierre

[sean0118]

find another ferrite like that you glued (the glue won't repair the ferrite by the way, the current won't flow in that ferrite core) and 'clone' the transformer if you got time.not easy but doable, you just need the copper wire with same diameter and the paint for electrical isolation (sorry I don't know the word for this type of paint ).

Why wouldn't gluing the old ferrite in work? It might add a small air gap where the glue is, but the original bobbin is assembled from two pieces anyway...

I think reverse engineering and rewinding a new transformer might be a bit too advanced (I'm just guessing). 

The PSU most likely has other issues if gluing the ferrite in didn't work.

[perieanuo]

find another ferrite like that you glued (the glue won't repair the ferrite by the way, the current won't flow in that ferrite core) and 'clone' the transformer if you got time.not easy but doable, you just need the copper wire with same diameter and the paint for electrical isolation (sorry I don't know the word for this type of paint ).

Why wouldn't gluing the old ferrite in work? It might add a small air gap where the glue is, but the original bobbin is assembled from two pieces anyway...

I think reverse engineering and rewinding a new transformer might be a bit too advanced (I'm just guessing). 

The PSU most likely has other issues if gluing the ferrite in didn't work.

because the currents are circulating through the ferrite body.your glus is for sure a glue that doesn't restore the current path, acts like an insulator, see the theory of high frequency transformers

[perieanuo]

so if you can't clone him, buy a new one.
glued won't work it's a fact.
if you find some conductive glue, maybe, but it may heat depending on glue and how thin can you get to assemble the broken parts.
thicker the conductive glue, bigger the series resistance he will introduce, bigger the heating losses.

[AdamOfAus]

Oy vey. Yeah it was a smalll amount of glue and i strapped it in with tape.

There is a guy in Adelaide who does takes your old one and some cash for the same unit, might go that way.

I think reverse engineering and rewinding a new transformer might be a bit too advanced (I'm just guessing). 

The PSU most likely has other issues if gluing the ferrite in didn't work.

Yeah that's a good guess, lol.

[TheMG]

so if you can't clone him, buy a new one.
glued won't work it's a fact.
if you find some conductive glue, maybe, but it may heat depending on glue and how thin can you get to assemble the broken parts.
thicker the conductive glue, bigger the series resistance he will introduce, bigger the heating losses.

Conductivity has absolutely nothing to do with it! The whole point of ferrite is that the tiny individual magnetic particles are isolated electrically from one another in order to keep eddy currents (which would result in loss of efficiency and increased heating) down to a bare minimum. Ferrite is non-conductive!

When gluing the pieces back together, you want to keep any gaps to an absolute minimum, and place the chunks in their original location as much as possible. So using a thin heat-resistance glue will work fine.

I have glued ferrites back together as temporary repair on a few occasions with negligible difference in performance

The PSU most likely has other issues if gluing the ferrite in didn't work.

That is the most likely scenario. With a large chunk of the core missing, that would have drastically changed the characteristics of the transformer, particularly its inductance, if the power supply was powered on this way, I wouldn't be surprised if some of the components let out the magic smoke. Especially the primary side switching transistors and associated components.

As for how the damage occurred in the first place, I'd say it could be manufacturing defect or rough handling during manufacturing. Hairline fracture in the ferrite could expand over time with thermal cycles until a whole chunk of it just falls right off by gravity. Ferrite is quite brittle material.

[max.wwwang]

Looks like a major crash site. I'm interested to follow on how it goes. 

I've torn apart a similar transformer, its ferrite cores were EE type. I guess if properly heated by a heat gun or similar, not too difficult to take off the old and put a new matching pair on. Where they are joined by glue can be broken with reasonable force. (but I used brutal force!) The conductor should usually be multi-wire one, I think.

Re glue, I'm not an expert. But I guess any high strength thing would do, like epoxy or similar. I thing the biggest thing is to keep the gap as small as possible. But as a temp repair, this should not be too much to worry about. Of course, there might be specialised electromagnetic ones but beyond my knowledge.

Attached two photos of when I did the crime.

(It’s worth note that the joint of the middle leg of the two E’s is without glue. This is because here is inaccessible when fitted. Of course, it’s not impossible to apply glue before quickly putting them in place but I think it’s a design decision not to do so taking into account the pros and cons. One of the cons obviously is that if using glue the gap becomes bigger-I’m aware for the visible glue joints the glue is not in the way of the magnetic flux but as a bump sideways which makes the gap to the minimum.)