Samsung LE40m87BD ... no backlight

[Porto]

Re: Samsung LE40m87BD ... no backlight

UI807 outputs at pin 2 and pin 3 drive the input pin of UI802S pin 2 and pin 3.

'That UI802S IC is a FAN7382VH36.

Only pins 1 and 8 have 12v, the other pins range from 0 to 0.15v.'

UI807: 'Those pins are outputting 4.9 volts, so that IC is OK.'
So something does not make sense to me if the output pins of UI807 has 4.9V, then the pins on UI802S cannot have only 0.15V unless both inout pin of UI802S are shorted out.

I did a continuity test to ground on that FAN7382 IC and this came out of it:

TV off / standby:

only pins 4 (COM) and 6 (Vs: high voltage floating supply return) connect directly to ground (my DMM 'beeps').

TV on:

pins 1 and 4~8 all connect to ground (my DMM 'beeps'), with resistances varying from 0.0 to 5ohm. Pins 2 and 3 have a resistance of 380ohm and I hear some hissing coming from the inverter transformer when touched with the probe.

Does this mean that FAN7382 is internally shorted / blown?

[budm]

Re: Samsung LE40m87BD ... no backlight

You cannot do continuity or resistance test with power being apply to the unit under test, you can easily damage your meter.
The only time you do the test when the unit has power is when you do the Voltage test.

[Porto]

Re: Samsung LE40m87BD ... no backlight

You cannot do continuity or resistance test with power being apply to the unit under test, you can easily damage your meter.
The only time you do the test when the unit has power is when you do the Voltage test.

Ah, ok, I keep learning!

[Porto]

Re: Samsung LE40m87BD ... no backlight

Can the logic board cause the BL not to turn on and/or switching the TV on and off automatically?

I ask this because that shielding on it is becoming quite hot when the TV has been turned on for a while.

[budm]

Re: Samsung LE40m87BD ... no backlight

BL-ON is generated by the main board. The shielding on the main board processor?
On your post #1 you show Inverter ON/OFF (BL-ON) is present.

[Porto]

Re: Samsung LE40m87BD ... no backlight

Yes, BL-ON signal is there but maybe something else is causing this on that logic board.

[budm]

Re: Samsung LE40m87BD ... no backlight

As long as the BL-ON is present, and the inverter circuit did not detect the fault the lamps and supply Voltage to run the circuit is present, then the lamps should stay on as long as BL-ON is present.
So did you verify that the lamps did not flash on?

[Porto]

Re: Samsung LE40m87BD ... no backlight

As long as the BL-ON is present, and the inverter circuit did not detect the fault the lamps and supply Voltage to run the circuit is present, then the lamps should stay on as long as BL-ON is present.
So did you verify that the lamps did not flash on?

The BL in the screen isn't flashing at all and ATM I don't have a CFL to test the inverter outputs. What kind of lightbulbs can I use also?

[budm]

Re: Samsung LE40m87BD ... no backlight

Just a small twisted CFL lamp as shown in the link in post 17.

[Porto]

Re: Samsung LE40m87BD ... no backlight

Just a small twisted CFL lamp as shown in the link in post 17.

Can I use this lamp, it's a working one but that doesn't matter I guess?!





OFFtopic: I even found the schematic of it:

[budm]

Re: Samsung LE40m87BD ... no backlight

That should work, just solder a stiff solid wire to the base of the lamp like I have shown in my pictures.
You will then stick the probe in the HV socket, hold on to the glass section of the lamp with one hand and then turn on the TV, if there is HV the lamp should flash on for seconds.

[Porto]

Re: Samsung LE40m87BD ... no backlight

That should work, just solder a stiff solid wire to the base of the lamp like I have shown in my pictures.
You will then stick the probe in the HV socket, hold on to the glass section of the lamp with one hand and then turn on the TV, if there is HV the lamp should flash on for seconds.

The HV is working, I got this CFL hooked up and it was going lit very bright on both of those HV outputs. I couldn't even hold it for more than 2 seconds because the glass was becoming very hot very quickly; I even burned my arm in the process due to leaning (stupidly) to the housing with it when the lamp activated. DOH!



But that means the HV is present and there must be something wrong with either the inverter balancer board or the CCFL's themselves. I guess this balancer board can be disconnected from the CCFL's but he sits kinda firmly into the sockets. The balancer board doesn't seem to have any fuse on it.
There is another cable leading to it with VCC_12v and 10v 'LD'. The other three pins labeled 'FB, GND, NC' have no voltage on them.

[budm]

Re: Samsung LE40m87BD ... no backlight

Good, the balancer board and the lamps will be next, since you do have HV that means you MUST have seen the Lamps lit up for seconds.
It is unlikely that all the Balancer transformers and all the lamps will be all bad. It has to light up and then protection kicks in.

[Porto]

Re: Samsung LE40m87BD ... no backlight

Good, the balancer board and the lamps will be next, since you do have HV that means you MUST have seen the Lamps lit up for seconds.
It is unlikely that all the Balancer transformers and all the lamps will be all bad. It has to light up and then protection kicks in.

Nope, no flash at all. It is like the voltage doesn't reach the balancer board and/or CCFL's or the lamps themselves are dead. Do you know how many lamps there are in this model? I see 20 output sockets, is one socket also one lamp?

[budm]

Re: Samsung LE40m87BD ... no backlight

Reseat the HV connector on the balancer board, then check the resistance between the two top pins of those balance transformers to see if any one of them show open circuit.
Pictures provided by shopjimmy.

Samsung SSB400HA20V

[Porto]

Re: Samsung LE40m87BD ... no backlight

Reseat the HV connector on the balancer board, then check the resistance between the two top pins of those balance transformers to see if any one of them show open circuit.
Pictures provided by shopjimmy.

Samsung SSB400HA20V

Nope, none of them is open, they all measure in the range of 270~285Ohm.

But I think I screwed up and toasted the inverter transformer.

I had unplugged that HV connector to take a look at the back of that inverter board but forgot to replug it; it managed to 'hide' between the housing and the inverter board and I didn't saw that. I turned on the TV and as soon the HV was getting through, the transformer began to hiss loud and that plug was half fried and black; I guess it was arcing because it was pushed against the housing (ground) by the inverter board. Now the resistance between the two HV pins is only 22 ohm, also the resistance between those pins and ground is 11 ohm. If I turn on the TV that plug is instantly set on fire so .... not good!

You agree it's dead or are those resistances normal?

I don't know how to check that transformer another way. I sure am not comfortable now to do that HV test with the CFL bulb.

I think the CCFL's are dead anyway so maybe it's time to give up on it before I burn down the house.

[budm]

Re: Samsung LE40m87BD ... no backlight

At this it sounds like the HV section is toasted.
I am not sure how much money you will wnat to spend to get back where we do not have the lamps light up but have HV from the inverter board.
But at least now you know how to find out if the HV is present or not in the inverter section using the lamp probe.

[Porto]

Re: Samsung LE40m87BD ... no backlight

At this it sounds like the HV section is toasted.
I am not sure how much money you will wnat to spend to get back where we do not have the lamps light up but have HV from the inverter board.
But at least now you know how to find out if the HV is present or not in the inverter section using the lamp probe.

It's not worth it. This was already an old TV which already had that pesky on/off switching, maybe also due to already bad/arcing CCFL's. Would be nice if the BL worked but now it's even more worse than it already was and brand new, and also better, TV's are sold for peanuts these days. Stupid mistake of me but maybe it's not a good idea to mess with these kind of things in the middle of the night.

But thanks for all the help, I'm much wiser and confident now.

[Porto]

Re: Samsung LE40m87BD ... no backlight

Hi Budm,

A little follow-up.

Because I couldn't resist it, I desoldered the main inverter transformer (TI801S) and measured the two secundary windings and they both gave an OL, so 'open' winding. So I guess the transformer is definately toasted... pity.

[goodpsusearch]

Re: Samsung LE40m87BD ... no backlight

Hello, I got this model for free:

https://www.badcaps.net/forum/attach...1&d=1642369772

My model is LE40M86BD, NOT LE40m87BD, but the inside boards look exactly the same.

I have similar issues with the original poster.

This is what happens exactly:

Eyou should see the backlights flash on for seconds then the protection circuity will kick in to shutdown the high Voltage.

I can verify that I can see for a second the image on the screen, then the screen gets dark.

Then I get a spotlight and I can see that there is actually image on the monitor, it's just the CCFL backlight that turned off.

I already disassembled monitor and noticed that during the above test, I can smell something burnt from the area where the SSB400HA20V is located.

I don't have experience with LCD TV repair.

I only have limited LCD monitor repair, but nothing advanced, mainly recapping.

The caps look OK on the psu and the mainboard.

So, I don't know how to tell if the issue is in the SSB400HA20V board or one of the CCFL lamps itself.

I painted a blue arrow here:
https://www.badcaps.net/forum/attach...1&d=1642369772

showing where the burnt smell seems to come from.

So, what should be my next step? I absolutely don't want to make things worse with that TV set.

40" Full HD still has some value here.