BN44-00265A schematic needed

[mu2]

Hi,

I'm working on a Samsung LN46B550K1FXZA where the backlights attempt to turn on. Cycles four or five times with the backlights briefly coming on - then stops trying.
I found 2 bad FDPF12N50UT mosfets so far and would like to identify some of the surface mount parts in that area.
I found schematics for boards with similar numbers but the BN44-00265A is different.
Thanks.

Mike

[Ltank]

Re: BN44-00265A schematic needed

elektrotanya.com/ has it. I found it but Sat. internet is too slow for me to doownload and post it

[mu2]

Re: BN44-00265A schematic needed

I did download the service manual for the set but unless I missed something, the schematic for the power supply wasn't there.
I can't find a listing for just the power supply.

Mike

[Ltank]

Re: BN44-00265A schematic needed

Well I tried

[budm]

Re: BN44-00265A schematic needed

What is the board not doing?

[tw2005]

Re: BN44-00265A schematic needed

Hi,

I'm working on a Samsung LN46B550K1FXZA where the backlights attempt to turn on. Cycles four or five times with the backlights briefly coming on - then stops trying.
I found 2 bad FDPF12N50UT mosfets so far and would like to identify some of the surface mount parts in that area.
I found schematics for boards with similar numbers but the BN44-00265A is different.
Thanks.

Mike

not precisely what you asked for but the B version. looks fairly similar, different transformers and looks like the FDPF12N50 have been increased to 16A versions FDPF16N50

SJ shows 265A,265B,& 266A boards interchangeable,

Even if it's not 100%, if you look up datasheets for the same components in the B version and find out the case marking, maybe then compare that data back to what you see on your board?

[budm]

Re: BN44-00265A schematic needed

It is strange that the backlights will flash 4~5 times in sync with cycling on and off without going into inverter shutdown mode and stays in shutdown mode after fail in first attempt. I wonder if the BL_ON is going up and down or the PS_ON is cycling.
Were those two MOSFETs failed as shorted?
C1804 (0.68uF 500V) in rev B board is also known for loosing its capacitance.
BTW, the PS_ON and the Inverter ON/OFF pins have pull-up resistors, so if you disconnect the cable between the power supply/inverter board board, the backlights should come on the minute you plug the TV into the AC outlet.

[mu2]

Re: BN44-00265A schematic needed

Budm,

The mosfets did not fail shorted. They have no gain when testing with my Cricket. The heatsinks were discolored from high temperature around the mosfets. When I removed the parts there was very little thermal paste to transfer the heat.
I had two FQPF13N50C that I thought would be a good sub but my symptom is similar now. I haven't researched the difference between the FQPF and FDPF lines.
I still need to pull the replacement parts out again and see if they also failed.
I haven't spent a lot of time on this set and I'll use your suggestions to scope some signals and check the cap. I did get the BN44-00265B and saw the mosfet upgrade. I think that my version uses different driver circuitry before the mosfets. I didn't have much luck crossing the surface mount component markings to something that made sense- that's why I wanted the schematic.
Thanks again for all your responses.

Mike

[mu2]

Re: BN44-00265A schematic needed

Budm,

I did a little more testing.
The .68 uf cap is at location C1825 on this version of the power supply - it tests good.
I was off on the number of cycles - the set cycles 3 times then shuts down.
Disconnecting the cable between the power supply and inverter makes no difference - I have the same 3 cycle problem with the backlights flashing on briefly and then shut down.
The inverter on/off pin is also cycling from 0 - 5 volts. The 5 volt and 12 volt supplies appear ok.
So, is the main board bad?
Could the eeprom be corrupt? Can I stick a blank eeprom in it's place and then hopefully go into the service menu and set parameters?

Mike

[mu2]

Re: BN44-00265A schematic needed

Hi,

Still no luck on this Samsung. I pulled the replacement mosfets out and they are ok.
I did find a thread on the internet describing practically the same problem.

http://www.justanswer.com/tv-repair/...ing-black.html

The tech and the set's owner finally gave up.

Anyone ever fix this symptom? Bad bulb?
Anyone know the location and part number of the eeprom?

Thanks,
Mike

[budm]

Re: BN44-00265A schematic needed

"The inverter on/off pin is also cycling from 0 - 5 volts." This signal is generated by the main board, so something on the main board is not right. You can use external 3VDC pwoer source to force on the inverter, use 2 AA and a 100~500 Ohms resistor in series with the + of the batteries to feed into the BL_ON PIN, but you must remove the bl_on wire from the inverter board so the main board will not force it in the LOW condition.

[mattstolte]

Re: BN44-00265A schematic needed

any updates on this tv? I got the same issue I have tried replacing everything and can not get it.

[mu2]

Re: BN44-00265A schematic needed

I gave up on the set and sent it back to the recycling center.
Sorry.

Mike

[mattstolte]

Re: BN44-00265A schematic needed

Yeah I don't understand what it is I changed everything. Is it possible panel is bad. Even when power supply and inverter alone is connected it does it. Yesterday I changed inverter as last thing and it stayed on for like 30 mind then I turned it off. Today I went down to turn it on and it did it again.

[mattstolte]

Re: BN44-00265A schematic needed

Figured it out thanks to you tube. After I had the set for over a month and changed everyboard. You have to cut the jumper jp854 I tried it on the new and old power supply works great

[tom66]

Re: BN44-00265A schematic needed

Figured it out thanks to you tube. After I had the set for over a month and changed everyboard. You have to cut the jumper jp854 I tried it on the new and old power supply works great

Rarely a permanent fix on these -- it just hides a problem which will come back (low PFC voltage tripping UVP circuit)

[mattstolte]

Re: BN44-00265A schematic needed

Where is the low voltage coming from then?