TV SMPS BN44-00473A keeps turn on and off

[sn4k3]

Hello,

I have a BN44-00473A from a TV, the voltage output is not fixed, the psu keep turn on and off or is trying to turn on, but due some problem it can't mantain and keep reset. Every three seconds voltage rise about 5V to 12V (on B12V line) but my meter is not fast enought to cath that voltage spike because it drop to 0V almost instantly. I can hear a fast click sound every time when voltage rise, maybe from a relay or switching noise. The psu is able to light up the LCD backlight at that rise moment, like an instant flash. Same happen with 5V Line.
High DC Voltages also variate from 160V to 140V at that moment but never drop to 0V

I have no experience with SMPS boards but i test all caps and they are good, visual inspect with microscope seens good and new, no signs of damage.
I also have the datasheet, if someone can give me some guideness would be cool as i don't have experience troubleshooting this modules but i would like to have.

PS: Main board had a short under CPU which i already replaced and is fixed now. Maybe the SMPS killed the main board with that unstable voltage?
All measurements was made only with SMPS connected to AC without any other conections to modules

Regards

[budm]

Re: TV SMPS BN44-00473A keeps turn on and off

It sounds like you have problem in the STBY power supply (A5V) section.
This board is know for having bad connections on those rivet through hole solder pads, especially on the transformer's leg.

[sn4k3]

Re: TV SMPS BN44-00473A keeps turn on and off

It sounds like you have problem in the STBY power supply (A5V) section.
This board is know for having bad connections on those rivet through hole solder pads, especially on the transformer's leg.

Can you advice what components i should check?
I have measure all TS801S legs 7 and 8, they are near 0v dc.
DS853 center leg gives 2.6V min and 5V at spike.

I have checked all transformer legs and they are good. Why they are bad? The board is single side print and pins go directly to the hole and soldered at bottom
Is there any point on the board i can inject 13V or 5V to check if is a hot or cold problem?

[budm]

Re: TV SMPS BN44-00473A keeps turn on and off

Those boards are know for bad solder joints, if you inspect with magnifying glass you will see ring developed around the solder joints.
So right now you A5V power supply is swinging high and low?

"I have measure all TS801S legs 7 and 8, they are near 0v dc." those two pins are high frequency AC output, no DC.

Startup/running cap CS802 should be check for capacitance and ESR, or just replace it. DS804 needs checking.
CS855 has good capacitance and low ESR?
Snubber diode DS803 also need to be check.
Right now A5V power supply section must be repaired first.

[sn4k3]

Re: TV SMPS BN44-00473A keeps turn on and off

Those boards are know for bad solder joints, if you inspect with magnifying glass you will see ring developed around the solder joints.
So right now you A5V power supply is swinging high and low?

"I have measure all TS801S legs 7 and 8, they are near 0v dc." those two pins are high frequency AC output, no DC.

Startup/running cap CS802 should be check for capacitance and ESR, or just replace it. DS804 needs checking.
CS855 has good capacitance and low ESR?
Snubber diode DS803 also need to be check.
Right now A5V power supply section must be repaired first.

Yes i can see the ring under microscope, i have resolder the joints just in case.

CS802: 25.21uF, Vloss: 0.7%, ESR:0.11Ohm
CS855: 604.4uF, Vloss: 1.2%, ESR:0.00Ohm
DS804: 0.5153V (Voltage Drop)
DS803: 0.4740V (Voltage Drop)
DS853: 0.2427V (Voltage Drop)

Diodes was tested on board, should i remove them to better test?

[sn4k3]

Re: TV SMPS BN44-00473A keeps turn on and off

Voltage across + and - BD801S is 325VDC
Fuse FP802S is rated at 250V, 325VDC messured, and not blown, why?

[budm]

Re: TV SMPS BN44-00473A keeps turn on and off

"Fuse FP802S is rated at 250V, 325VDC messured, and not blown, why?"
Are you saying that you measure the DC Voltage between the two ends of the fuse and it shows 325VDC???
If that is the case, the fuse has open circuit.

[sn4k3]

Re: TV SMPS BN44-00473A keeps turn on and off

"Fuse FP802S is rated at 250V, 325VDC messured, and not blown, why?"
Are you saying that you measure the DC Voltage between the two ends of the fuse and it shows 325VDC???
If that is the case, the fuse has open circuit.

No, i put the negative lead on terminal (-) of BD801S and positive lead on fuse, tested both sides and they are 325VDC. As i told fuse is good, i test first for continuity, not open. I also tested with two different multimeters just to discard any error from equipment, both show same voltage

[budm]

Re: TV SMPS BN44-00473A keeps turn on and off

I am just trying to understand your statement regarding to the Voltage reading on the fuse.

"CS855: 604.4uF, Vloss: 1.2%, ESR:0.00Ohm" That is very odd capacitance value and ESR of 000 Ohms. What is the capacitance value as printed on the cap?

[sn4k3]

Re: TV SMPS BN44-00473A keeps turn on and off

I am just trying to understand your statement regarding to the Voltage reading on the fuse.

"CS855: 604.4uF, Vloss: 1.2%, ESR:0.00Ohm" That is very odd capacitance value and ESR of 000 Ohms. What is the capacitance value as printed on the cap?

Well i'm just following the schemantic from PDF, as i can see the AC voltage get rectified to DC at BD801S after that the positive side pass the diodes DP802 and DP803 and go directly to the fuse (FP802S T2AL/250V), thats why i have checked, fuse is rated at 250V and 325V is passing there.

CS855 spec: 560uF 25V
I tested the caps using this tool: https://www.banggood.com/DANIU-3_5in...p-1083042.html
Might have a small error due cheap equipment but when testing with a good capacitance meter the results doesn't vary that much and this give the ESR value too

[Thushara Wijesingha]

Re: TV SMPS BN44-00473A keeps turn on and off

Hello,

I have a BN44-00473A from a TV, the voltage output is not fixed, the psu keep turn on and off or is trying to turn on, but due some problem it can't mantain and keep reset. Every three seconds voltage rise about 5V to 12V (on B12V line) but my meter is not fast enought to cath that voltage spike because it drop to 0V almost instantly. I can hear a fast click sound every time when voltage rise, maybe from a relay or switching noise. The psu is able to light up the LCD backlight at that rise moment, like an instant flash. Same happen with 5V Line.
High DC Voltages also variate from 160V to 140V at that moment but never drop to 0V

I have no experience with SMPS boards but i test all caps and they are good, visual inspect with microscope seens good and new, no signs of damage.
I also have the datasheet, if someone can give me some guideness would be cool as i don't have experience troubleshooting this modules but i would like to have.

PS: Main board had a short under CPU which i already replaced and is fixed now. Maybe the SMPS killed the main board with that unstable voltage?
All measurements was made only with SMPS connected to AC without any other conections to modules

Regards

I had same issue with my SMPS. I replaced ICM 801. and capacitors around the IC. It's working smoothly now.