PCB mounted transformer How to identify?

[groovejet]

Ive put in to search engine ALL and various parts of the codes on the transformer but to no success
What is the best way to go about this
its got 5 tappings on one side and 4 on other, ithink it must be the 3.5 v transformer.
The board is out of a LG Smart tv that has no power or standby light ,but i do have a 3.5v on the rail but nothing else.
so i wanted to check both transformers on board . only because i noticed some crusty gunk on the 4 tapping of the transformer.
tried putting up more pictures but pc was playing up

 

[kellys_eye]

The transformer is unlikely to be at fault - they rarely fail and if they do they usually do so with some 'proper' signs of failure like melted tape and burned wiring.

What you have is a typical SMPS board - complete spare boards are often available and for those with fault symptoms if you Google the make/model of set with "repair kit" attached you usually get a few results. These kits contain the 'usual suspect' component parts to repair the board.

Otherwise, state the make/model and post more pictures of the board and we might be able to assist further.

 

[(*steve*)]

The problem is more likely to be with those black cylindrical things (capacitors) or the devices connected to the silver heatsinks (MOSFETs and/or diodes).

 

[groovejet]

none of the caps are bulged, but i havnt got a cap meter, so i suppose ill try and get a rough idea from using my dmm, , but looking over the web theres that much stuff about testing i dont know where to start.
Ive merssed about and used diode mode on the caps , which has fed in a small voltage then ive turned it to dc volts and watched the reading lower, which has given a indication of the cap charging and discharging.
or am i wrong?? i dont profess to be any good at this,but does this give any indication of how the cap is?

 

[groovejet]

The diodes that i tested gave decent readings. The Zeners gave .7v and o/l.
and rectifiers .5 and o/l but when i tested the bigger diodes i got conflicting results. i now know they are Schottky diodes as pass both ways but was unsure.
Iwas getting .2v forward bias and .2 rising to .9 then it would go open line?? Is this a dead one?

 

[(*steve*)]

Iwas getting .2v forward bias and .2 rising to .9 then it would go open line?? Is this a dead one?

I bet you find the same thing when you measure a capacitor...

The diode is connected to a capacitor in the circuit.

Show us a photo of the whole board (both sides) and we can try to point you at the most likely things.

Have you checked the fuse?

 

[kellys_eye]

The usual fault with capacitors is that their internal resistance rises which requires a special device to measure. When it gets 'real bad' the capacitors can bulge or even explode but a bad one might simply 'look' ok and you'd never know.

But, as you have discovered, SMPS's aren't the easiest things in the world to work on - the fact that they rely on a feedback loop often confuses people and makes repair complicated BUT there are also items you can change 'just-in-case' that may simply fix the fault.

More details (pictures, make/model etc) and we could probably talk you through the whole process.

 

[groovejet]

nice one , ill get onto it tomorrow

 

[groovejet]

Heres more pics and model number
No standby light or power.
2 x 3.5v lines from power board to logic board .... nothing else.
240vac at board and fuse ok
one jumper wire buirnt ( my doing!!!)

 

[groovejet]

So when i tested power board i get 3.5v on two connectiond. These i presume are standby ??? So why do i not get a stadby light??
Thankyoui

 

[kellys_eye]

The only board we're interested in is the PSU - the rest of the pictures are of no use. We might also need to see the reverse of that board too - they sometimes mount parts on the rear.....

Save yourself some trouble:

https://www.tvparts.co.uk/eax645605011-7-eay62770401-lg-32lm3400-power-supply

although currently out of stock.....

but your set is a 32" TV with only 720p resolution. You could probably buy a used set with full 1080p for that £30........

Show some closer pictures of the PSU board and one of the rear.

 

[groovejet]

really that cheap

 

[groovejet]

One really big piece of info i forgot to tell.......I did have a standby light until i re soldered the larger pads on the board, theyre like the rivoty looking pads i just flower more solder on and then no standy....OOooops

 

[kellys_eye]

What did you do to cause the short on the link wire?

TBH I wouldn't advise you to do anything else to this board. Your lack of knowledge/skill to work on this type of board could be dangerous to yourself, potentially others too.

Have a look for a spare board on eBay - you might find it cheaper than the link I put up for you. But spending £30 on a spare board for a set that is as-good-as obsolete (not being 1080p does you no favours....) is £30 that could go towards a used set that wouldn't cost much more...

 

[groovejet]

'Thanks for your help i really appreciate you taking time to teach a newbe.
This tv will either get fixed or stay in my parts bin.
I did cause a short when i was probing. I WAS GETTING ROUND ANOTHER COMPONENT TO TEST AND I PUSHED THE PROBE TO FAR AND IT TOUCHED THE JUMPER WIRE
I do this because i enjoy it not because im being thrifty with a cheap tv thats not worth fixing.
Im not going to hurt myself, im competent in alot of mechanical and electrical things, and have two time served trades behind me.
All ive been is honest, i made a mistake but im not going to start poking around with my hand in places where theres 240v or 320vdc i aint that brave.
WHEN!! I do fix it , itll be my pc monitor till it dies a long life.
At the minute its not even 3 years old so id like to try and get it working, for experience and fun more than anything

 

[kellys_eye]

I WAS GETTING ROUND ANOTHER COMPONENT TO TEST AND I PUSHED THE PROBE TO FAR AND IT TOUCHED THE JUMPER WIRE

The only way it could cause a 'short' like that is if your meter was in a high current measuring mode - it may also happen in a low resistance mode (but why would you be measuring resistance on a 'live' board?) Maybe the probe tips don't have sufficient insulation? All told it shows a little 'carelessness' that could be fatal. I have 'concerns'...

Anyway, we have yet to determine if that short caused any additional issues with the board.

If you want to proceed then you really should get some basic knowledge of how an SMPS works - once you do you will be able to determine where to measure the basic input voltage(s) i.e. AC at the bridge rectifier input, DC across the smoothing capacitors then - on a 'dead' chassis - check the switching device for shorts (it is probably ok given the main fuse is ok though).

A schematic will be almost essential - have you searched for one yet?

The likely suspect is the main controller IC501 but the schematic would make testing around the device much easier. Failing the correct schematic you might find an 'application note' for the controller IC (IC501) which offers clues. Can you post details of that controller IC?

 

[groovejet]

ok thanks. i get it you dont know me ... but i asure you im not into habbit of frying myself.
And i wasnt measuring resistance , i was actually testing bridge rectifier. Now it was a few days ago but it tested fine, 240v and something like 320vdc respectively.
my broadband is playing up ...gone slow. so ill get onto these things , thanks

 

[(*steve*)]

And i wasnt measuring resistance , i was actually testing bridge rectifier. Now it was a few days ago but it tested fine, 240v and something like 320vdc respectively

Ok, but how do you know the bridge rectifier was working properly? I would have tested the bridge rectifier with the power off.

I also assume that you were not holding any more than one probe when measuring these voltages.

 

[groovejet]

yea i tested it with no juice on diode mode and looked good. SO later on i was checking standby voltages and i though id check rectifier also. when i was checking voltages i had one lead clamped to neutral when i was testing hot side.
And one lead on the chassi when i was probing standby etc, but i got nothing apart from 3.5v

 

[groovejet]

schmatic of EAX64560501(1.7)
click on image then click on ...Open in new window then you can zoom in for better look... cheers
UPDATE- For some reason it doesnt let you zoom in to all images?? Any ideas?