Samsung 24" power supply BN44-00195A first stage voltage?

[andy2]

The power supply is made by Dong Yang - BN44-00195A
It is a standard power board for Samsung 245B 245BW and 2493HM

The diagram is here:
https://cdn.badcaps-static.com/pdfs/...f8a620fd8c.pdf

Question:
What voltage should I expect on the first stage of that switcher - on that big cap in the center of it?

On the diagram it is called PFC_OUT and it is the voltage measured directly on that cap which per diagram is CP803 and should be 150uF and on the board it says CP801S and it is 82uF cap. It is the same part.

The first stage is an obvious boost converter - so I expect the voltage to be quite high. But how high? Anyone?

[tom66]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

Around 385V to 400V.

[sabre504]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

Hi
Us is lower voltage 120v(i think) so should see about 165/168v or there abouts

[selldoor]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

NB we are talking vDC here

[jetadm123]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

In standdby mode, it should read around 165VDC. Once the power supply turns on, it should rise to around 390VDC.

[budm]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

What is it not doing?

[andy2]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

Thanks, indeed after reading the TDA4863G description today the DC voltage I asked about should be in range of input AC times 1.41. It is input dependent. For the US ~120Vx1.41=170DC or so, not more. But I am puzzled by this voltage increase you keep mentioning - why would it increase with load? It shouldn't... Unless the measurement is sensitive to noise. The maximum voltage on that cap shouldn't exceed the mentioned value so with 240V rated AC input it should be maximum 338V DC or so. I think. For a 450V rated cap 338V is somewhat high anyway. Am I missing something here?

[budm]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

The voltage is increase is due to that this power supply has PFC Voltage booster circuits. At standby, the cap will have 170Vdc, whne PS on is applied, the votage will get kick up to around 400VDC.
So what is it not doing?

[selldoor]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

You inadvertently answered your own question earlier - google and read up on PFC
Power factor correction which boosts the voltage to the high figures mentioned.

[andy2]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

Thank you guys. I am glad I found this forum. -)

[andy2]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

The voltage is increase is due to that this power supply has PFC Voltage booster circuits. At standby, the cap will have 170Vdc, whne PS on is applied, the votage will get kick up to around 400VDC.
So what is it not doing?

There was a loud explosion noise from the monitor and it stopped working. -)
The board has 1 fuse blown and I just started on it. No visible damage though.
Thank you for that jpg. It's very very helpful.

[Toasty]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

"There was a loud explosion noise from the monitor and it stopped working."

-and-

"No visible damage though."

Typically do NOT go together. Look CAREFULLY.

Check for cracks in casings of the NTC thermistor NT811S (Inrush Current Limiter), bridge rectifier BD801S, the main PFC switcher FET QP801S, and the other FETs QM801/802. Check the bung of the mains cap for distortion or bulging.

T

[budm]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

I second that to Toasty comments.

[selldoor]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

We have usually requested pictures of the boards before now. Without them it is difficult.
We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246

[andy2]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

thanks guys, you are great, but I am gonna take it slow, because I have to work. I'll not hesitate to ask about specifics later.

[Toasty]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

Forgot a few things...

There is a blue or yellow rectangular plastic cap around center, between the mains cap and the output transformer on that PSU. It's about 3/4" x 1/4" x 3/8". Marking is 12nJ 600v or similar.

Make sure there is no brown caulk/glue around its legs. The glue becomes conductive with heat/age and that cap is carrying the drive to the switching transformer.

Also, check the resistors in front of QM802/803. I've seen them burn out if either of those FETs die. 33Ω & 0.22Ω

Then, flip it over and with the main power jack/switch to the right, check the lower left quadrant for a burned 100Ω SMD resistor, just below the black horizontal line. Jewelers loupe and/or eyes <30 years old needed.

If it's out, 24v will not come up. The 24v Zener is probably shot along with the 1P transistor next to the resistor. That circuit is a safeguard to monitor the 24v & 5.3v lines and trips if there is a disparity between them. It will cause the unit to shut down or not start if damaged. It sends a signal to the opto which feeds the protection leg on the IC MC33067P / ICM801.

T

[Duncanbest]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

My idea:

1.follow Toasty's suggestion : check components

2.check the 5.2V first: remove DB803 RM801 RM831
power on --> 5.2V is on or not

3. 5.2V is on ,install DB803 ---> check the voltage on CP803 ,PFC works or not

4. PFC works ,install RM801 RM831 then focus on 24V & inverter circuit

[andy2]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

Question:

My plan was indeed to remove the RM801 first and check the 5.2V. But since you mentioned the other parts removal - why do I need to remove RM831 with DB803 removed? I thought removing the DB803 diode cuts off the power M_Vcc so there should be no voltage on pin 15 of the ICM801 and the voltage on enable pin 9 would be low - am I correct?

Also - since the PRC_out shunt RM801 is taken out - then the QM801 and subsequently QM802 would not be powered so the 24V side would not power up anyway. Right?
I got to start working on it. I'll keep you posted.

[Duncanbest]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

Question:

My plan was indeed to remove the RM801 first and check the 5.2V. But since you mentioned the other parts removal - why do I need to remove RM831 with DB803 removed? I thought removing the DB803 diode cuts off the power M_Vcc so there should be no voltage on pin 15 of the ICM801 and the voltage on enable pin 9 would be low - am I correct?

Also - since the PRC_out shunt RM801 is taken out - then the QM801 and subsequently QM802 would not be powered so the 24V side would not power up anyway. Right?
I got to start working on it. I'll keep you posted.

1.Yes. My idea is without M_Vcc you can focus on 5.2V circuit ,so remove DB803.
2. No voltage on pin 15 of the ICM801 and the voltage on enable pin 9 would be low --->yes
3.since the PRC_out shunt RM801 is taken out - then the QM801 and subsequently QM802 would not be powered so the 24V side would not power up anyway. Right? --->yes

[andy2]

Re: Samsung 24" power supply BN44-00195A first stage voltage?

update:
The 11N60 QP801S mosfet is blown, but that was not a primary problem.
I also saw a burned shunt - it was covered with glue so initially it was hard to see - but now I connected the power with QP801S removed and the DB803 disconnected but everything else in place and I saw a huge spark going over that broken shunt.

The shunt number is J823 and it is not shown in diagram. Only on the board.
It is close to that big cap. Right next to RB801S resistor but it is a separate circuit.

That shunt is connecting that M_Vcc circuit, but the circuit is not as on the diagram. There is something not right about this circuit especially on the PFC side. It doesn't match the print at all. I was trying to follow the print to figure were that voltage came from, but it is hard. This circuit is entirely different than on the diagram.

If I lift BM801 - there is no current flow and no sparking - but that also cuts off the power to the 5.2V control chip - ICB801S. This is because the BM801 is located somewhat between the DP802 (Diode past the PFC MOSFET which blew) and the RB806 on the diagram, but on the board it says RB801.
The board doesn't seem to be equipped with DT806. So with no BM801 - there can't be any 5.2V.
BUT - when the RM801 is disconnected and BM801 connected - there is no sparking.

But why would that broken jumper spark like that? The gap is like 1/8 of an inch and it sparks like crazy. There must be a gazillion volts over it.

Those part numbers are very confusing, its not very logical way of numbering parts.
So I'll just repeat - all the above is WITHOUT the DB803 diode.

I figured the broken jumper is located more or less in place where that M_Vcc circuit has the input designator on page 2 of the diagram. So it looks like it sparks between CM807(diagram)/CM805(board) and CP804(board) - I don't want to guess which one that is on the diagram. The board seems to have connected together positive sides of the caps numbered CP804(board), CB812(board), pin8 of tda4863 and that goes to that sparky jumper on the other side. Crazy stuff.

By the way - with RM801 disconnected - the 5.3V is present - but it is unstable, meaning it fluctuates slowly between 5.17V and 5.3V.
Also - there is ~16V on the PFC side of the broken jumper - it also fluctuates and I suspect it must be coming through that TDA4863 so it is probably also bad.