Samsung LN40A500T1F

[dietzcj]

Got this free TV from a friend who knows that this is a hobby of mine.
Samsung LN40A500T1F
It has the blinking red light on the power button.
It will not power on at all. I thought for sure that it was the Main Board, so I bought one on ebay for $35. Turns out to be a different problem as the same symptoms continue.
I don't see any bulging caps on the power supply so I assume that is not the problem.
Last time I was working on a TV I could get the inverter and the backlights to shine verifying that the power supply is good. I cannot however remember how to do that. I think I unplugged the Main Board from the power supply and then plugged it in. But I think I am doing it wrong.

Here are some pics if someone would like to take a look and help me out.

My main goal is to just locate the defective board and or repair the board (if it is simple as ordering something from DigiKey).

[budm]

Re: Samsung LN40A500T1F

Not sure if this power supply-inverter combo board has built-in pull up resistors for the PS_ON, BL_ON or not, you can disconnect the cable between the power supply board and the main board to see if the backlights will come on when you apply AC to the TV.

[dietzcj]

Re: Samsung LN40A500T1F

Yeah, budm, I did that and they didn't turn on.
Bad power supply ?
Can I mimic that power supply to the inverter somehow ?

[budm]

Re: Samsung LN40A500T1F

It may not be since the board may not have the pull-up resistors. Do you have the power supply part number? It should be something like BN44-XXXXX, then I can look up the diagram for it.

[dietzcj]

Re: Samsung LN40A500T1F

bn4400199a

[dietzcj]

Re: Samsung LN40A500T1F

more pics

[budm]

Re: Samsung LN40A500T1F

OK, this power supply does not have pull-up resistors, so for you to test the function of this power supply/inverter board you will have to use 1K resistor between PS_ON pin and STB5.1V pin, and another 1K resistor between inverter on/off (on/off) and the STB5.1 pin.

[dietzcj]

Re: Samsung LN40A500T1F

Does that mean I have to cut one of the cables on that ribbon, or do I just unplug the ribbon and "hot jump" it with a couple of small alligator clips ?
Thanks for the help btw.

[johnboy1313]

Re: Samsung LN40A500T1F

Use 1K resistors between the holes in the connector

[dietzcj]

Re: Samsung LN40A500T1F

I think you mean to attach to the under side of the board with the 1k resistor on the power supply (Ps-ON to the Stb5-1v) and then on the interver board (inverter on/off (on/off) and the STB5.1 pin).

[dietzcj]

Re: Samsung LN40A500T1F

Okay I will try that once I dig up a couple of 1k 's.

[dietzcj]

Re: Samsung LN40A500T1F

so do I try it with the main board plugged in ?

[tom66]

Re: Samsung LN40A500T1F

Main board should be unplugged.

[dietzcj]

Re: Samsung LN40A500T1F

is a half watt carbon film resistor 1k ohm the right resistor ?
I have both metal film 1 watt and carbon film.

[dietzcj]

Re: Samsung LN40A500T1F

so like this ? See photo.
but the other end of the ribbon cables shown here should be unplugged from the Main Board.

[tom66]

Re: Samsung LN40A500T1F

That looks good.

[dietzcj]

Re: Samsung LN40A500T1F

okay, the result is that the back lights power on.
So that means that the power supply and the inverter boards are good ?
And the main board is bad ?

[dietzcj]

Re: Samsung LN40A500T1F

Is there a way to troubleshoot the main board and T-con ?

[tom66]

Re: Samsung LN40A500T1F

In general yes you can check things like voltage regulators and DC/DC converters, but more than likely you will find that the firmware or eeprom is corrupt which would be challenging to fix.

[dietzcj]

Re: Samsung LN40A500T1F

So you would just recommend that I get a replacement Main board ?
Don't worry, I won't hold your feet to the fire if you say yes and it still doesn't fix the problem.
I would just like your honest opinion.