Samsung LN32A300J1d - no backlight power from PSU board BN44-00150A

[ngth82]

Good evening everyone -

I have a Samsung LN32A300J1D in the garage. The unit turns on with the standard Samsung start up sound, but there is no video on the screen as the backlights are not turned on. I have confirmed that there IS video however -- I can definitely see video output on the display if I shine a flashlight at an angle against the panel.

There is NO voltage along the thick blue and white wires to the left or right balance boards. To verify that there isn't something shorting out, i disconnected the blue & white wires at the PSU board and measured the output voltage at the respective connectors - CNI801 and CNI802. I read zero volts.

The PSU board part number is BN44-00150A and looks like the image that i attached from ShopJimmy. The connectors in question are in the lower right corner in the image.

Does anyone have the service manual for the BN44-00150A? I ideally would like to debug the backlight inverter voltages instead of purchasing a new power board.

The only thing I've done to this power board thus far is replace three caps on the cold side. I thought it would just be a really easy fix...

Thank you,
Thomas

[budm]

Re: Samsung LN32A300J1d - no backlight power from PSU board BN44-00150A

Are yoi getting about 400VDC between the two legs of either one of the main filter caps in the primary side when the TV is on?
Are you getting the Inverter on signal, >2.5VDC?
BTW, do not try to measure the High Voltage on the inverter output connector unless you want to ruin your meter.

[ngth82]

Re: Samsung LN32A300J1d - no backlight power from PSU board BN44-00150A

Hi Budm -

Sorry for the delay. I've been very busy at work and haven't been looking at the Tv.


The Inv_on signal is 5.25V.

The two main filter caps are through hole components, but the leads are flush with the board. I'll have to take it apart further Friday when I just have more time and solder wire leads up to it. I'm not too keen on having to hold this board while it's on to measure those caps.


The regulated output to the main board looks good though - I see 13v, 5.4v and 12v.

I'll update again on Friday (or if I manage to find some time during the weekdays)

Thanks,
Thomas

[R_J]

Re: Samsung LN32A300J1d - no backlight power from PSU board BN44-00150A

I just repaired a LNT5265FX/XAC that had one of these (BN44-00150A) boards, It had a few 1000/25v caps replaced before but 2 were missed, (the 2 at the top of the board) the fault was intermitint and low backlight, I replace all the 1000 uf 25V caps. in the secondary and its working fine.

[ngth82]

Re: Samsung LN32A300J1d - no backlight power from PSU board BN44-00150A

Are yoi getting about 400VDC between the two legs of either one of the main filter caps in the primary side when the TV is on?
Are you getting the Inverter on signal, >2.5VDC?
BTW, do not try to measure the High Voltage on the inverter output connector unless you want to ruin your meter.

Hi Bud -

I finally had a chance to come back to this today. I found topside locations where i can measure the positive side of the primary caps. The heatsinks are my hot ground. Yes, i get +381VDC across the caps. The total capacitance on that rail is about ~370uF (i see two 180uF caps) so that sanity check looks okay.

The Inverter On signal is 5.25V.

I currently have the power board pulled off and its on my work bench. I've had no luck thus far trying to find the schematics/service manual for this board (BN44-00150A), so i'm tracing out the components for the inverter logic and hoping to find a similar Samsung power board with reference designators that closely match to aide in debug.

Thanks,
-Thomas

[ngth82]

Re: Samsung LN32A300J1d - no backlight power from PSU board BN44-00150A

I just repaired a LNT5265FX/XAC that had one of these (BN44-00150A) boards, It had a few 1000/25v caps replaced before but 2 were missed, (the 2 at the top of the board) the fault was intermitint and low backlight, I replace all the 1000 uf 25V caps. in the secondary and its working fine.

Hey R_J -- thanks for the reply to this thread.

I really have a hard time in seeing how the caps from the secondary has any effect on the inverter ON/inverter voltage circuitry controlling the hotside inverter voltages. (Just bare with me).

The INV_ON signal comes from the main board and on to the power supply board at connector CN1805. Pin 1 of this connector is a trace (now at 5.25V) that goes to the far left side of the board along the top edge that looks like it's part of the inverter voltage control circuitry. (no direct connections between the secondary large caps and the INV_ON circuits). See attachment...

I found an exact matching board on eBay for $65. But i'm torn between spending the cash and making a small profit from the TV, or just sending it to the Goodwill for eWaste (after salvaging parts of course).

-Thomas

[ngth82]

Re: Samsung LNT4661FX/XAA - no backlight power PSU BN44-00150A (corrected tv model)

And I seem to be a complete dumbass --

The TV model number TN-T4661F
The model code is LNT4661FX/XAA

I must have mixed up the photos as I was looking at multiple Samsung TVs a few weeks back.