Samsung LE32N73BD - 2 seconds to black

[tom66]

Got this one today.

Very nice TV with USB and camera card slots.

No bad caps as I had thought it might have, although mostly CapXon...

All supplies are stable. Uses 24V inverter, 24V measures 24.41V.

However it has Darfon transformers, so I suspect the fault lies with one of these.

Pictures soon.

[Mr Bill]

Re: Samsung LE32N73BD - 2 seconds to black

I'd put money on it being a bad transformer. Every inverter issue i've repaired to date the inverter board was made by darfon.

[tom66]

Re: Samsung LE32N73BD - 2 seconds to black

Thanks Bill. I will have a look at it later tomorrow.

I fixed a similar issue with a 26" Samsung.

[tom66]

Re: Samsung LE32N73BD - 2 seconds to black

Okay, some preliminary tests.

All transformer secondaries test okay.

Just noticed BL_ON signal; tested that and it goes to 0V when the backlights go out. So, clearly, this is the problem.

The signal is generated by the main board.

Neither the card reader, DVB or T-con affects it; unplugging either results in the same symptom.

Display brightness varies a bit during power up. It varies in discrete steps though.

I suspect the main board, will look closer into the problem and see if I can replace the main board for fairly cheap.

Found someone with a vaguely related issue. http://www.youtube.com/watch?v=3jnTZnVD0t8 Main PCB needs replacing according to comments. Main board diagnosis is a bit out of my league. I am waiting on my new Rigol DS1102E to debug it.

[tom66]

Re: Samsung LE32N73BD - 2 seconds to black

Well, this is a stumper. However, I am pretty sure the main microcontroller is the issue, and that it is part of the shutdown procedure. It is detecting something it doesn't like.

I've discovered if I jumper the MCU crystal the TV will stay on for longer and stuff will show, but it only shows it for the first 3 seconds then freezes up with a green screen. It's also mostly broken up.

So, possibly the main video processor has a problem, and MCU is detecting it.

Or MCU is not sending some init signal to the main processor so it doesn't initialise nicely.

I will try and grab the service manual for it.

[cadiman]

Re: Samsung LE32N73BD - 2 seconds to black

All of the darfon inverters I have replaced had issues with the detector circuit.

The transformers were ok and the mosfets driving them were good too. It was always in the detector circuit of the inverter board (sometimes from the transformers) and not the tv mainboard.

I would always test for the 3 to 5volt turn on signal from the mainboard and it was always there.

After replacing the darfon inverter board the tv would work fine.

This was always the case with the 23 to 26 inch lcd tvs.

A faulty transformer would normally be the cause of the dectector circuit shutting down
but I have had alot of problems with the detector circuit alone.

[tom66]

Re: Samsung LE32N73BD - 2 seconds to black

In my case, the on/off is dropping out. i can get it to stay on longer by crashing the MCU. So I'm not sure what to make of it...

[multimeter]

Re: Samsung LE32N73BD - 2 seconds to black

i think a data sheet for the main cpu is needed here,have you checked vcc into the chip?,is the voltage stable?,good oscilations on the crystal?.

there should be a signal that comes from the main cpu that outputs to the bl_on signal,im guessing this is missing,data sheet could show output stages of the cpu,if that bl_on voltage is dropping off ,its def the main board.


hmm ,maybe a voltage reg slipping its voltage

[tom66]

Re: Samsung LE32N73BD - 2 seconds to black

I will upload the SM tonight; have just dug it out and it has a schematic, which is useful.

[multimeter]

Re: Samsung LE32N73BD - 2 seconds to black

"I am waiting on my new Rigol DS1102E to debug it."



nice scope !,if you dont mind me askin how much ? (excited gremlin)!

[tom66]

Re: Samsung LE32N73BD - 2 seconds to black

"I am waiting on my new Rigol DS1102E to debug it."



nice scope !,if you dont mind me askin how much ? (excited gremlin)!

£335 shipped from UK. Sold my old HP 54501A to a friend.

[tom66]

Re: Samsung LE32N73BD - 2 seconds to black

Dammit, someone else bought the main board before me for £37.

So right now I can't source a new main board. TV is a paperweight.

Will probably sell it on to someone who can source one... maybe direct from Samsung... Or maybe the main board is repairable.

[multimeter]

Re: Samsung LE32N73BD - 2 seconds to black

whats the main board part # tom?,i got loads of sammy boards,if i got one il whack it in the post

[tom66]

Re: Samsung LE32N73BD - 2 seconds to black

whats the main board part # tom?,i got loads of sammy boards,if i got one il whack it in the post

BN94-01077B

or

BN40-00080A

MOSEL MMS

Thanks

[multimeter]

Re: Samsung LE32N73BD - 2 seconds to black

BN94-01077B

or

BN40-00080A

MOSEL MMS

Thanks

just checked most of my boards are bn41 prefix,but check this out

http://www.ebay.co.uk/itm/BN94-01077...#ht_2548wt_968

[tom66]

Re: Samsung LE32N73BD - 2 seconds to black

just checked most of my boards are bn41 prefix,but check this out

http://www.ebay.co.uk/itm/BN94-01077...#ht_2548wt_968

Yeah, I found that... but I can't really afford to spend £50 on a board when I'm not certain about the fault.

[alexanna]

Re: Samsung LE32N73BD - 2 seconds to black

All of the darfon inverters I have replaced had issues with the detector circuit.

.

A faulty transformer would normally be the cause of the dectector circuit shutting down
but I have had alot of problems with the detector circuit alone.

What type of signal dose the inverter feedback circuit produce ?
Is it an on/off signal or PWM? Could a signal be substituted to rule out the inverter feedback circuit?

[multimeter]

Re: Samsung LE32N73BD - 2 seconds to black

What type of signal dose the inverter feedback circuit produce ?
Is it an on/off signal or PWM? Could a signal be substituted to rule out the inverter feedback circuit?

if the signal comes from the main board,id imagine it will be an on/off signal,where the voltage goes high,prob about 3.3v,if its coming from the main cpu,id be inclined to pull out that on signal,and inject its own voltage onto that rail,to see if things come up,it may at least verify that it is the mainboard at fault,which i think it is.

considering tom has bridged the xtal,and the symptoms have changed,im assuming he has checked for a sine wave coming from the xtal,if the cpu aint happy then it wont send out the high voltage to the inverter to turn on,on these boards there is not a lot that can be changed apart from a few caps ,voltage regs etc,i have tried changing cpu's on these boards,and made a complete dogs ear of it .

[tom66]

Re: Samsung LE32N73BD - 2 seconds to black

Yep, all xtals are nice and stable. I will wait for the Rigol to verify (only have a crappy analog scope temporarily, since I have sold my digitising HP.) I suspect though that some firmware somewhere has been corrupted or messed up (possibly bad over-the-air update) but I cannot be certain. Wish there was a "safe mode" jumper or something that would put TV into a mode ready to accept firmware, but no.

[multimeter]

Re: Samsung LE32N73BD - 2 seconds to black

tom,you said earlier,that there was a usb port,have you tried for a download off samsung website?it may show what version the firmware is,and compare to yours,a longshot i know.

although i dont think its a firmware issue