Bench Test Samsung BN44-00621C Power Supply Board

[Nicktronic]

Hey!

I've got this power supply board that's had some components replaced and I'd like to confirm all the voltages before I install it.

This is what I have when I plug in the board on the bench;

1 - N.C. - 0 VDC
2 - PWM_DIM4 - 0 VDC
3 - N.C. - 0 VDC
4 - PWM_DIM3 - 0 VDC
5 - GND - 0 VDC
6 - PWM_DIM2 - 0 VDC
7 - B13V - 0 VDC
8 - PWM_DIM1 - 0 VDC
9 - B13V - 0 VDC
10 - ECO_ON/OFF - 0 VDC
11 - Vamp - 0 VDC
12 - BLU_ON/OFF - 0VDC
13 - Vamp - 0 VDC
14 - GND - 0 VDC
15 - GND - 0 VDC
16 - GND - 0 VDC
17 - B5V - 0 VDC
18 - A5V - 5.3 VDC
19 - B5V - 0VDC
20 - PS_ON/OFF - 3.3 VDC

Since there is voltage on the PS_ON/OFF, I assumed a High to Low enable and shorted the 3.3 to GND. Heard a relay click, but no other voltages appeared on any of the pins above. Is there something I'm missing?

[R_J]

Re: Bench Test Samsung BN44-00621C Power Supply Board

What are the components that were replaced? You seem to only have standby voltage, check the voltage across one of the main filter caps, (CP803) The voltage should be 165vdc in standby and around 385vdc when ON if the pfc circuit is working.
I suspect the main switching section is not working, check that CP814 is not burnt (likely covered in silicone) also check that solder connections on both transformers TM801CS and TM802CS

[Nicktronic]

Re: Bench Test Samsung BN44-00621C Power Supply Board

I bought this repair kit because the TV was not turning on sometimes. Sometimes it would turn on but turn off after an hour or two. Also, could hear relays clicking on/off, but the TV wouldn't turn on.

https://www.shopjimmy.com/samsung-bn...nt-repair-kit/

The items in the repair kit are:

ICM801S
QP801C
QP802C
CS854
RS807
ICS801CS
CM868
CS851
CM850
CM853
ICP801S
DS804
DS807
DS808
DS810
DS812

I tried what you said R_J, in Standby, filter caps read 389VDC. When I short the PS_ON 3.3VDC to GND, a relay clicks and the voltage on the filter caps slowly discharge to OVDC. CP814 is NOT burnt. Solder joints on the TXFMRs look good.

[R_J]

Re: Bench Test Samsung BN44-00621C Power Supply Board

The board will be turned ON normally, when you ground PS_ON you are turning the board OFF, 389vdc on the main filter indicates the pfc circuit is working. So with the PS_ON high, check if you have B5v and B13V
If you are still having problems I would likely change CS806, CP820 & CS804, and maybe CS851, they are in the standby circuit and can dry up over time. Other caps I might change in the primary circuit are the four small electrolytics around and including CM807.

[Nicktronic]

Re: Bench Test Samsung BN44-00621C Power Supply Board

Thanks R_J. With PS_ON high, the results are what I indicated in Post #1, so I guess I will go with the caps replacement.

[Nicktronic]

Re: Bench Test Samsung BN44-00621C Power Supply Board

Ordered the caps from Digikey. Be a few days, but I'll let ya know how it goes...

[R_J]

Re: Bench Test Samsung BN44-00621C Power Supply Board

Have you tried the board back in the tv? Here is a similar schematic (BN44-00622B), not exact but might help, If the power supply board worked before but was intermittent It should be the same now, so check your work to make sure there are no bad connections or shorted pins on an ic etc.

[Nicktronic]

Re: Bench Test Samsung BN44-00621C Power Supply Board

Yeah, it did work (intermittently) before. I did check my work, but will look again.

[Nicktronic]

Re: Bench Test Samsung BN44-00621C Power Supply Board

So my work looks good. I didn't explicitly mention this, but in Standby (5VDC and 3.3VDC available), the VDC across the filter caps is 168VDC.

The FET driver ICs (ICM801S and ICP801S, i think?) don't have anything on Vcc to GND, any thoughts on where/how those voltages are generated? One of those generates the switching voltage for the two main TXFMRs right?

Apologies if I'm mixing things up, I'm trying to understand and explain at the same time!

[R_J]

Re: Bench Test Samsung BN44-00621C Power Supply Board

IN post #3 you had 389v on the main cap, now it is 168v, When the voltage is 389v the PFC circuit is/was working, when the voltage is 168v the PFC is NOT working.
VCC for ICM801S and ICP801S comes from the standby transformer and is controlled by a transistor, In the schematic of the 622B (and on your board), DS802 is the supply diode, QS801 is the regulator/switch which supplies the VCC_AUX (17vdc) to those ic's and is controlled via PCS802S optocoupler. (PS_ON/OFF) controls QS861 which turns the optocoupler on/off
QS861 also energizes RL801S which supplies A/C to the main bridge BD801S

Remember that voltages on the primary side are reference to HOT ground, not COLD (chassis) ground

A correction to my post #2:
On this power supply RL801S controls the main supply voltage so in standby the main cap will have near 0 volts, not 165v

[Nicktronic]

Re: Bench Test Samsung BN44-00621C Power Supply Board

Ok, I'm going to try to explain what I know now.

First, ICP801CS got shorted (accidentally somehow) and was bad. I replaced it now have ~390VDC, so PFC is working.

Second, my board does not have the same ICM801CS chip as the schematic in Post #7. My board has an Fairchild FAN7621. This chip provides gate drive signals to a highside and lowside MOSFET (FDPF18N50T x 2). The HO gate drive signal (Pin 3) measured 14.2VDC on pin 3. The signal on the LO line (Pin 14) looks like a drive signal I think (See pic). The Drain of the lowside FET is connected directly to the source of the highside FET and also connected to TXFMR TM802CS. I've got ~390VDC at the Drain of the highside FET and GND at the source of the low side FET......

.....I'm thinking one of those FETs are bad? Gonna pull them and take some ohm readings..

[Nicktronic]

Re: Bench Test Samsung BN44-00621C Power Supply Board

Forgot the attachments for post #11..

[Nicktronic]

Re: Bench Test Samsung BN44-00621C Power Supply Board

FETs tested good. The NEW ICM801CS chip that I installed from the repair kit was bad, FML. I put the original back in and the board works fine now. I think what ultimately was causing my problem were the caps R_J said to replace in Post #4.

Thanks alot!!

[R_J]

Re: Bench Test Samsung BN44-00621C Power Supply Board

Good to here it's working, hope that solved the intermittent problem

[Nicktronic]

Re: Bench Test Samsung BN44-00621C Power Supply Board

It did! Working beautifully now, thanks for your help.