Hello, got Samsung smart tv with bad power board BN44-00503A, diagnosed bad MOSFET F13NM60N (QP801S) and 5A fuse, after replacing both, replaced mosfet burned out immediately, fuse is ok, maybe somebody knows what can be checked prior trying one more?
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Last edited by xfox; 06-14-2021, 10:40 PM. -
Re: Samsung smart tv bad power board BN44-0503A
Looks like also burned two resistors one RP810 (68 Ohm) and RP809 (30 Ohm)Attached FilesLast edited by xfox; 06-14-2021, 10:57 PM. -
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Re: Samsung smart tv bad power board BN44-0503A
Remove MOSFET QP801S, then:
Check all the components off the "gate" of QP801S, replace components as needed.
The PFC Control IC (ICP801S) may be shorted.
Check capacitors CP818 and 819 for short
Check diodes DP802, DP803, DP808 for short, and that they don't reverse bias.
Check Rectifier Diode BD801S on the DC side for shorts, for a good diode reading on all 4 terminals and that it does not reverse bias. When checking for a good diode reading expect the + and - diode reading to be about .9 instead of .4 to .6.
Let us know what you find.
I just repaired a BN44-00502A which is similar to yoursThey call me......."threadkiller"
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Re: Samsung smart tv bad power board BN44-0503A
So what I did, I replaced resistors RP810 and RP810 and QP801S, after that board not exploded and LED light started to blink (5 times double blinks), nothing on backlights connector (0V), checked backlight with LED tester, looks good and working
mainboard connector:
PIN14 (Power On_off): 3,2V
PIN12 (A5V): 5V
CP818 and CP819 - no short
DP802, DP803, DP808 - no short, reverse ok
BD801S no short, shows 0.555 one way only (soldered)
ICP801S - not sure how to check
PIN6 - PIN7 - 29 Ohm
PIN5 -PIN7 - 76 Ohm
PIN5-PIN6 - 47.6 Ohm
One more thing, had no proper resistors, so used 68Ohms to replace 30Ohm (2x68Ohm parallel connected so got 34 Ohms)
)
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Re: Samsung smart tv bad power board BN44-0503A
What voltage do get on the main capacitor when you try to turn on the TV?
We're reaching the limit of the help I'll be able to give you on this power supply. I'm no ace tech, but since I just repaired a similar board I thought I'd try to at least help with what I learned.
Check the quality of your solder joints, and check all the solder joints on any item attached to a heat sink. Look for ring cracks in the solder joints upon these items. It sounds to me like the PFC circuit isn't boosting the voltage. If you used flux to solder the items you replaced make sure it's all cleaned off the board.
I missed some flux/residue on mine and it was causing similar problems, my TV turned off and gave 2 blinks then wouldn't turn on at all until I thoroughly cleaned all the flux off the board. It's been aces ever since.They call me......."threadkiller"Comment
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Re: Samsung smart tv bad power board BN44-0503A
Nothing on main capacitor, all looks okComment
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Re: Samsung smart tv bad power board BN44-0503A
The only other item I know of that may be deficient is the PFC IC, but I hasten to suggest you replace it as I think you would be doing so without knowing for sure if it's actually bad. I still don't know how to test them. They survive shorted MOSFETs about 70% of the time. Mine was OK on my 00502A power supply.
I apologize but we've reached the limit of my knowledge. Can anyone else step in here and take over? Any further suggestions by me would only be guesswork and I'd really like to see this poster get the right answers and get this fixed.They call me......."threadkiller"Comment
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Re: Samsung smart tv bad power board BN44-0503A
Wish I could help you more.They call me......."threadkiller"Comment
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Re: Samsung smart tv bad power board BN44-0503A
If you have "nothing"(no voltage) on the main filter, your main fuse is likely open. But this can not be the case if you have A5V standby voltage.
Recheck the voltage across the main filter cap CP814S, Then check the voltage across CS805, Then check the voltages on QS801 (using hot ground) QS801 supplies the PFC_VCC to ICP801S (around 16 volts)Last edited by R_J; 06-17-2021, 06:53 PM.Comment
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Re: Samsung smart tv bad power board BN44-0503A
CP814S - 163v
CS805 - switching from 14v to around 19.5v
QS801 - same as CP814 163vComment
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Re: Samsung smart tv bad power board BN44-0503A
163v across the main cap indicates the board is either not turned ON or the pfc circuit is not working. Is the main board connected? if it is, disconnecting it should force the power supply ON.
CS805 should be on the collector of QS801, this should be a small smd transistor. The base of qs805 is controlled by the optocoupler PC802S It turns on QS802s which acts like a switch and a regulator, it supplies about 16 volts on its emitter if it is working (power supply ON)Last edited by R_J; 06-21-2021, 11:58 AM.Comment
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Re: Samsung smart tv bad power board BN44-0503A
Tried disconnecting, same measurementsComment
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Re: Samsung smart tv bad power board BN44-0503A
Marked ground on attached photo with blue
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Re: Samsung smart tv bad power board BN44-0503A
Oh, sorry... So voltage is 13.25V without main board connected and switching from 13.25 to 19v with main boardLast edited by xfox; 06-22-2021, 01:12 PM.Comment
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Re: Samsung smart tv bad power board BN44-0503A
Voltage on picture, so it's switching from one to another, looks like main board is trying to reset itselfComment
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Re: Samsung smart tv bad power board BN44-0503A
This why we disconnect the main board, the power supply should turn ON with the main board disconnected, this will eliminate the main board as the cause of the problem.
with the main board disconnected, the PS_ON line will be taken high to A5V by the pull up resistor, this will turn on QQ852 which also turns on PC902S, the output of PC802s will turn on QS801 and supply a constant (14v) to the pfc icp801s.
If the PFC circuit is indeed working you will get around 385VDC across CP814sLast edited by R_J; 06-22-2021, 10:47 PM.Comment
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Vizio e601i-A3 - Has Sound and Display, But No Backlight - Bad Power Supply Board or Bad LED Bulbs ?I was given this TV from my great uncle. He said it just wouldn't turn on one day out of nowhere, replaced the TV, and gave it to me to possibly fix and use for myself.
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The screen seems to blackout and stay black, but with a flashlight I can see the display.
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Assuming... -
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