Samsung LE32B530P7W start up problem, fix with heat

[Fr3shGy]

Hello,

I just got a LE32B530 Samsung TV. Issue is: Standby blinking 5 times then it turns off.

Powerboard: BN44-00261B

I was able to find out that the issue is the PSU board. But now i am stuck. I replaced:

CM863 1000 uF 25V Cap
CS854 1000 uF 25V Cap
CM853 1000 uF 25V Cap
CM852 1000 uF 25V Cap

CM861 2200 uF 10V Cap
CM862 2200 uF 10V Cap

CM860 0.47 uF 50V Cap

But it is still not fixed. If i heat up the transistor with the heatgun ICM854 its the KA431A transistor, the TV works and the Inverter stays on untill i cool down the transistor.

I dont know what i can do right now, i mean if i heat the transistor up the tv works but i am sure the KA431A isnt the issue.

[ReeceyBurger123]

Re: Samsung LE32B530P7W start up problem, fix with heat

Cold solder joint ?

[Fr3shGy]

Re: Samsung LE32B530P7W start up problem, fix with heat

cant be i just replaced the KA431A still same result. If i heat it up the resistance decreases, then the inverter comes alive and the tv is runing fine.

[dick_barton]

Re: Samsung LE32B530P7W start up problem, fix with heat

PCM802S gone sluggish maybe??

[martino]

Re: Samsung LE32B530P7W start up problem, fix with heat

YOu are probably heating up a neighbor component with that heat gun. Maybe heat parts with the solder iron to pinpoint the sensitive one.Be carefull to NOT touch anything other then the body of each component! touching a leg of something might result in a big bang as it finds ground via the solder iron.

[Fr3shGy]

Re: Samsung LE32B530P7W start up problem, fix with heat

PCM802S gone sluggish maybe??

I changed them but still same issue.

YOu are probably heating up a neighbor component with that heat gun. Maybe heat parts with the solder iron to pinpoint the sensitive one.Be carefull to NOT touch anything other then the body of each component! touching a leg of something might result in a big bang as it finds ground via the solder iron.

i am using not exactly a heat gun, it is a small heat gun from a soldering station with a small nozzle around 1/4 inch. So it fits right around the KA431A transistor, i heat it up for just around 4 seconds to be sure that i am not heating other parts up. It well could be that i am heating something on the backsite up but there is only the CM864, or the QM852 but both seems to be fine i already tested them.

If i heat the KA431A up just for a few C° the resistance decreases. There sould be an issue with the parts connected to the KA431A either on the cathode lane or the anode lane. I am going to test these around the day but i am runing out of options...

[budm]

Re: Samsung LE32B530P7W start up problem, fix with heat

What dcV do you have at 'A' when it is working and when it is not? Also DCV at pin 1 of the 431 when working and not working.
You should also test those resistors RM866, 869, 870, Cap CM864; that 431 is used to shutoff (QM852) the 13V if it gets too high.

[Fr3shGy]

Re: Samsung LE32B530P7W start up problem, fix with heat

What dcV do you have at 'A' when it is working and when it is not? Also DCV at pin 1 of the 431 when working and not working.
You should also test those resistors RM866, 869, 870, Cap CM864; that 431 is used to shutoff (QM852) the 13V if it gets too high.

OK i ve got these measurements:

RM866 resistor (4704) 1,8 K ohms rising up to 5.3 K ohms until it stops
RM869 resistor (1022) 1,8 K ohms rising up to 2.0 K ohms until it stops
RM870 resistor (1016) 1,8 K ohms rising up to 8,6 K ohms until it stops

CM864 cap 1,760 uF

QM852 gate short (0 dcV) source (0,02 dcV)
QM851 gate (2,2 dcV) / source (0,5 dcV)

I am now going to get te DCV at "A" and the DCV at the 431

Seems like the QM852 is gone.
But why the K ohms on the resistors next to the 431 are rising like hell?

[budm]

Re: Samsung LE32B530P7W start up problem, fix with heat

TCap CM863 (1000uF 25V) is in parallel with the Voltage divider resistors so you will see the resistance rise up, and the resistors divider also has RM864 (2.2K) connected I parallel also so the resistance measurement in circuit will not be accurate.
QM852 gate short (0 dcV) source (0,02 dcV)' You should test this one off the board and test with meter in resistance mode.

[Fr3shGy]

Re: Samsung LE32B530P7W start up problem, fix with heat

TCap CM863 (1000uF 25V) is in parallel with the Voltage divider resistors so you will see the resistance rise up, and the resistors divider also has RM864 (2.2K) connected I parallel also so the resistance measurement in circuit will not be accurate.
QM852 gate short (0 dcV) source (0,02 dcV)' You should test this one off the board and test with meter in resistance mode.

Alright that make sense, i tested the QM852 off board

measurement of resistance:

QM852 gate (nothing) source (2,8 M ohms/ sometimes meter jumps to 100 K ohms)

[budm]

Re: Samsung LE32B530P7W start up problem, fix with heat

'QM852 gate short (0 dcV) source (0,02 dcV)' I do not know why you are seeing that then, you may what to test the same pads where you made the first measurement without putting the MOSFET back in to see if it still show very low resistance or not.

[Fr3shGy]

Re: Samsung LE32B530P7W start up problem, fix with heat

'QM852 gate short (0 dcV) source (0,02 dcV)' I do not know why you are seeing that then, you may what to test the same pads where you made the first measurement without putting the MOSFET back in to see if it still show very low resistance or not.

That was the first dcV measurement on board of the QM852, i thought it was a short on the gate because the QM851 had a 2,2 dcV on the gate.

i done the resistance measurement of the gate of QM852, and i got around 2,8 mill ohms. So i guess it should be fine. But i have a bad feeling about this transistor, it looks a bit dirty like it got heated up a bit.

I have a other N-Channel transistor to replace NIKOP3055LD but it only supports 25V the original AOI4184 supports 40V, so should i replace it? or will i blow up everything?

[budm]

Re: Samsung LE32B530P7W start up problem, fix with heat

OK, that MOSFET is OK, so more likely that 431 is sensing the 13V is too high or faulty sensing circuit trip level may be wrong due to the resistors variation.
As you can see they put two resistors RM869 2.2K, and RM866 47K in palrallel to get the right trip level by adding the 47K in parallel with the 2.2K so it must be quite sensitive that the added resistor has that high trimming resistor of 47K, you try adding another resistor to bring down the total resistance a little bit may be 5% or 10% less, you have to calculate the 2.2K//47K is first and then calculate the added resistor to bring the total resistance down by 5% ~10%.

[Fr3shGy]

Re: Samsung LE32B530P7W start up problem, fix with heat

OK, that MOSFET is OK, so more likely that 431 is sensing the 13V is too high or faulty sensing circuit trip level may be wrong due to the resistors variation.
As you can see they put two resistors RM869 2.2K, and RM866 47K in palrallel to get the right trip level by adding the 47K in parallel with the 2.2K so it must be quite sensitive that the added resistor has that high trimming resistor of 47K, you try adding another resistor to bring down the total resistance a little bit may be 5% or 10% less, you have to calculate the 2.2K//47K is first and then calculate the added resistor to bring the total resistance down by 5% ~10%.

Yes, that should be solving the issue. because if i heat it up the resistance of the 431 goes down just a few %.

so the RM869 2.2K and the RM866 47K is directly attached to the 431 in parallel?

Rtotal=2.2K x 47K/(2.2K + 47K)
Rtotal=2.1K total?

2.1K total down by 10% =1.89K

1.9K=2.2K x 47K x XK/(2.2K + 47K + XK)?


I guess i need some help with the maths.

[budm]

Re: Samsung LE32B530P7W start up problem, fix with heat

20k = 1.902k
18k = 1.882k
15k = 1.843k
12k = 1.788k

[Fr3shGy]

Re: Samsung LE32B530P7W start up problem, fix with heat

20k = 1.902k
18k = 1.882k
15k = 1.843k
12k = 1.788k

Ok i am trying to get 20k and the 18k resistor.
Should i attach the new resistor directly to the 2.2k transistor?

[Fr3shGy]

Re: Samsung LE32B530P7W start up problem, fix with heat

So some time is gone now, and i ve checked sth out.

my first intuition was wrong. I thought if i heat up the 431 the power board works fine.

So i separated the 431 and then i heat it up again but nothing happend.
There must be something underneath the 431 i heated up.

any tips are appreciated.