Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

[Badpowersupply]

Hello experts and technicians,

Maybe someone out there can be so kind to offer some expertise, information, advice?

BN44-00514A (P60SW_CPN)
Power supply from 60" Samsung 3D Plasma

The board seems to have full rectified dc voltage (360v) all over the hot side all the way through the presumed power factor correction transformers, fets, diodes, main caps and on to the main vs transformer and it's fets and the the smaller voltages transformer and it's fet ICE3BR2565JF.

But nothing to the cold side whatsover, no standby, nothing.

Being a student of electronics, am really trying to understand how the smsp works more and to fix it.

The leg of the current sense resistor for the ICE3BR2565JF (offline smps controller / startup cell) looks a little brown but seems to test ok at about .4 ohm.
You think it might be worth replacing the ICE3BR2565JF ?? Samsung had put some clear goop on the bottom of the pcb around this component only.

Most of the diodes seem to test ok and the fets too i guess.
All the caps look good, it's less than 2 years old

Any ideas much appreciated. Thanks

[stj]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

for a student of electronics you should learn 2 things.
1: small capacitors dont last and dont show visible signs of failure.
2: learn what startup capacitors are in relation to switching psu chips.

[ben7]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

Most of the diodes seem to test ok and the fets too i guess.

All of the diodes should test OK.

[selldoor]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

^^^^^^x2 ^^^^^^
plus pictures of both sides of your boards

[budm]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

Is your AC line Voltage around 250VAC?
And yes, good clear pictures of the bottom side of the board.
There may be a fusible resistor for feeding the B+ to the STBY SMPS section.

[Badpowersupply]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

Thanks for the replies!

Hi budm, Yes the line voltage is 230-250v ac.
I have included some pictures of the underside, thanks selldoor.

I'm not quite sure where the b+ standby fusible resistor may be as the standby appears to go through the same transformer as the regular 15v run voltages etc.

I see a fusable resistor in parallel with an ntc and the relay contacts. tests as a closed link (in circuit).

also another fusible resistor across (kinda) bypassing the inductor on the ac in side before the bridge recticifier. also test closed link (in circuit).

So I am wondering this resistor and ntc pass a low current into the psu to run the standby circuit which in turn should be able to power up the relay and allow further current through the same circuitry to fully power up the psu?

Hi ben7, why is it that the diodes should all test ok? i see norcal testing diodes while still in circuit, and there obviously quite important?

Hi stj, The startup capacitors are related to the IC (ICE3BR2565JF) which switches the transformer for the low voltages and standby power?

What i am unsure of is there seems to be 3 main sections to the conversion process:
1. after the bridge recifier the dc goes through two transformers? onto two fets which short those transformers? to ground and then to a diode (DP502) before going into the main caps positive side.
In this stage, the dc also goes through two large in series power diodes to the main caps positive side.

2. This dc from the main caps goes directly to both transformers which are supposed to transfer energy to the secondary side of the board. The larger of the two is for vs, has one optocoupler and two switching fets (one from - one from +).
The smaller transformer has one swiching fet which is inside the ICE3BR2565JF, a purpose built offline smps controller / startup cell. The fet inside this IC appears to short to ground through a .4ohm cs resistor the primary positive side transformer coil. This smps controller IC is definitly something to do with the standby, because it has some active burst mode which is supposed to offer very low standby consumption for the tv.
The is 5 optocouplers on this side of the board.

3. the secondary side is basically just rectified, filtered, sensed for feedback to the stage 2 of conversion process? Plus has the circuitry for standby power and communication of pson, vson etc through the optocouplers back to stage 1 and or 2.

Is stage 1 i am referring to just for power factor correction or is it also part of the smps.

Just somewhat confused there does not appear to be a dedicated standby circuit (that i am aware of) there are many other connections between the ac and the dc sides etc which must be responsible for it.
It seems much more complicated than the model that you get on the wiki page for smps lol.
Yet I am just a novice trying to learn so speaking to more experienced people is invaluable and amazing. Be happy to answer more questions or test certain aspects of the board or more detailed pictures etc.

Thanks guys

[rievax_60]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

It's a Flyback SMPS. Try to understand the basics first. Google for "flyback converter" , http://en.wikipedia.org/wiki/Flyback_converter
Do you use an isolation transformer? What test equipment do you have?

[Badpowersupply]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

Just did some further testing.
Where i previously stated 360v it actually is 335v. Sorry about that.
The ICE3BR2565JF has a VCC supply which is at 14.5v. It's datasheet specifies a VCC of between 10.5 - 25v.

[rievax_60]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

Pages 8 & 9 in the data PDF explains how start up bias is controlled. 14.5v could mean that the circuit is actually working, if its really flat line DC 14.5v. The voltage on the VCC pin needs to get to 18V first for start up to happen. Then it can drop to a lower voltage, no lower than 10.5V.

[Badpowersupply]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

Hi rievax, thanks for that information. It.s interesting you mention about the flat line 14.5v at Vcc pin because when I had the current sense resistor disconnected the voltage at vcc was fluctuating from 12.2 to 14.8v. But with cs resistor back in circuit, the voltage is a stable 14.5v. When I remove the ac power it goes to 15.5v for a couple of mins.
So maybe the problem lies in the circuit which is meant to charge the vcc to 18v?

Unfortunately don't really have any special equipment at this time except a multimeter. No isolation transformer. And thanks for telling me it is a flyback converter :-)

[rievax_60]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

I hope you have read the data PDF.
The bypass capacitor needs to get charged to 18V, then the IC jumps to life and then if nothing is wrong, the VCC pin needs to be externally sustained at something between 10.5V and 25V , usually by a rail rectified from a tertiary winding.
It really seems like it is working. find and check the rectified secondary rail for voltage.

[Badpowersupply]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

Hi rievax, thanks very much for the info, yes i have read the datasheet and am trying to make sense of the circuit.

There is no power on the secondary side at all. With the ac off, the secondary transformer (small one) appears to be shorted on the secondary side (as i specified in pic 1) is this a normal phenomenon?

Additionally there seems to be no path for the power to get from the secondary side back to this IC through the isolation barrier, only optocouplers.

I believe have found the capacitor in question, a 50v 33uF electrolytic, the symbol on bottom of pcb seems to havr 4z's (cx802) When applying ac it slowly charges (abt 2 seconds) to 14.5v no higher. which is insufficient to start the ic.

It's also difficult to follow the traces here because of black markings on the pcb. And confusing because from what i can see, this llittle circuit seems to get it's supply voltage form the negative side of the transformers primary? through DX805, a 4r7 resistor (rx802) then onto the vcc cap and ic vcc pin while being clamped by another resistor (rx803) and two zener diodes in series to ground.
I am on the right track? Should I replace this cap?

Also why do you recommend an isolation transformer for basic troubleshooting, is this for my protection or for the boards?

Many thanks!

[stj]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

for your protection.

[rievax_60]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

So the VCC isnt reaching 18V for start up. The IC itself could be faulty or anything connected between the VCC pin and ground. "ground" means the trace pattern that the negative pin of Cx802 connects too.
This includes Cx802, Dx805 and the zenners. See what resistance reading there is from the VCC pin to ground. Leaky diodes change resistance a lot when some heat is applied.
Be careful that the large HVDC capacitors have discharged before taking resistance readings or soldering. As well as the shock danger, accidental shorts will cause more damage.
Also, think twice before powering up while components are disconnected, this can cause more damage. an example is having the regulation feedback path disabled. Although some ICs are designed to protect for this.
Look at the example applications in the PDF to see how the VCC pin is powered after start up.

[stj]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

just try replacing the startup cap with a 47uf 50v 105' cap.

dried-up startup caps are very common and often under-sized for the purpose anyway.
does the datasheet recomend 33uf? probaby not.
it wouldnt surprise me if example diagrams show it as 100uf

[budm]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

The internal charge pump circuit inside the IC will charge up the start up cap til it reaches the required start up Voltage, then the primary winding of the power transformer will be driven by the MOSFET inside the IC, the charge pump will stop, the AUX winding of the transformer will not supply the Voltage to the startup cap to keep the circuit going. If the VCC drops below setpoint or gets too high beyond setpoint, the circuit will shutdown, it all explained in the spec sheet of the IC, I just give you the short version. Just think of it on how you start the car, the batteries supplies the power to start the car first, once the car started, the alternator takes over to supply the Voltage to run your car and to charge the batteries.
The Voltage form this AUX winding will also be fed to the switched transistors to supply the VCC to the PFC Voltage booster controller IC and also to the another switched transistor to supply the VCC for running the main SMPS circuit, these switched transistors are turned on when the PS_ON signal is sent from the main board, the signal is isolated from the HOT side through OPTO-ISOLATOR IC.
See the attached PDF for example of typical power supply setup.

[rievax_60]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

Another option is to do a direct test of the Startup Cell current, 0.9mA.

[Badpowersupply]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

Hey Guys, wow so much info to process, thanks so much!

> How to test the zeners in the vcc startup circuit? 2 of them in series to ground seem to read each about .67v on the diode scale and .43v when tested in series together.

> Resistance from vcc pin to ground is very high about 37k ohm.

> Replaced the startup cap with a 47uf 63v low esr. still the same vcc voltage.

I include a picture with some annotions about the state of the circuit.

Not quite sure how to test the startip cell current.
It's a shame I could not get a schematic for the exact psu.

It is making more sense slowly.
Maybe I should just make a psu from scratch out of dc dc converters lol.
Yet i am very keen to learn and have a hobby of keeping the plasmas and lcd out of the landfill!

Happy Christmas!
My best Christmas present would be to get this tv working

[rievax_60]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

Dx805 rectifies a voltage waveform from a winding on the transformer to power VCC after startup. Although leaky components can be illusive, I dont see anything too suspect. To rule out a possibly, cut the track leading away to the right from the + of Cx802. Double check that there are no other parts on the VCC pin other than Cx802. If the IC is ok, VCC should ramp up and down between 10.5V and 18V. You wont know for sure with a DMM but the fact that the voltage is going up and down implies that it's between 10.5V and 18V.
If there is still a problem, you can be more certain that the IC is faulty by soldering a 1K resistor across Cx802, power it up then measure the voltage across the resistor. Then calculate the current from the Startup Cell .

[rievax_60]

Re: Samsung SMPS no standby question BN44-00514A (P60SW_CPN)

Forget all of that for now, I just noticed your note about Dx805. With this diode out of circuit, you are seeing VCC to be likely to be ramping between 10.5V and 18V. This indicates that the diode is leaky and was holding down VCC. With Dx805 removed, you should measure some pulsing voltage on the output rails as the IC tries to start.