Samsung LNS3251DA won’t power on, no sound, no standby light-power board problems

[BmD_Online]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

Hi,
I have replaced the MOSFET and ICP801S.
I've build a Dim Bulb Tester (105W halogen bulb), and connected TV.

Once connected, TV seems to be in standby mode (red led on).
When I press start button, the bulb gets dim, but nothing happens to TV.
I've tried without dim bulb tester, and... fuse blows, and... circuit breaker trips (we say like that in english ?) !

I have spend to many money according to TV age, so I'm giving up !

Thanks to everyone who helped me.

[nomoresonys]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

Indeed BUT at this point it's not a matter of money anymore, it's getting to the bottom of the mystery why it is not working, right, lol.

[BmD_Online]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

You're right. I think I've burned MOSFET again with this attempt !
Right now, I'm a little upset.

Same power supply board is sold 15€ on eBay (refurbished) !
I think I'll buy it, check if TV works, and compare the two boards.

[nomoresonys]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

Just for fun, make sure all the caps n such you replaced, that none are in backwards and all have good solder joints and all the other solder joints are good.

[nomoresonys]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

Need to figure out what is blowing the fuse.

[nomoresonys]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

Did you check all the diodes?

[BmD_Online]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

Does the TV have to switch on when dim bulb tester is used ?
Can I create a short circuit connecting inverter to wrong connector (S or A) ?
I have double/triple checked all replaced caps.
All solders joints seems to be correct.
I will verify diagram. Maybe I've made a short when soldering SMD circuit (near to pin 4), but I don't think so.
I will try to check all diodes too. Not checked yet.

[vinceroger69]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

my dim bulb tester has no switch but i use a incandescent bulb i see you mentioned you used a halogen one im not sure if it works the same?
in your third picture can you clean all the flux off and post another picture of the same area

[BmD_Online]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

About dim bulb tester I mean when everything it right (after power supply repair), can I make TV power on and work correctly connected to dim bulb tester ?
Or I only can check for shorts, bu don't make it work fully.

I'm not sure my question is clear.

[nomoresonys]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

I believe if you have a short the bulb will light bright and stay bright, the tv should start with tester hooked up, prolly need a 60 watt or so incandescent bulb.

[BmD_Online]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

in your third picture can you clean all the flux off and post another picture of the same area

Here it is.

[budm]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

Edited: so the PFC MOSFET is tested as shorted again?

[BmD_Online]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

Without unsolder anything :
PFC MOSFET : 5.5 Ohms
bridge rectifier + - : 5.2 Ohms
bridge rectifier ~ ~ : shorted
RP819 : 0.8 Ohms (meter probes resistance is about 0.7)

I suppose I have to unsolder MOSFET, check it again and check bridge rectifier too ?
And, if I replace MOSFET, I have to replace ICP801S (tda4863-2) again ?
I have a second one, but I have to buy a new MOSFET and/or bridge rectifier if needed.

[budm]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

More likely that new MOSFET is blown again, it was OK when you first apply the power to the TV.
So did fuse blow the minute you bypass the lamp, or it blows the after the power switch is activated when the lamp is bypassed?

[BmD_Online]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

Yes, fuse blow directly when I bypass the lamp.

[nomoresonys]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

And your replacement fuse is an exact match?

[BmD_Online]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

Yes it is. 6.3A.
I've ordered new MOSFET. I'll come back when I receive and replace it.
We'll made controls at this moment.

[R_J]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

bridge rectifier ~ ~ : shorted

Once you have removed the shorted fet, re-check the bridge rectifier, even with the fet is shorted (5.5Ω), you should not have a short between ~&~ of the bridge. If the bridge is shorted, ac is being applied to the pfc ciruit.

[BmD_Online]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

Without unsolder anything :
PFC MOSFET : 5.5 Ohms
bridge rectifier + - : 5.2 Ohms
bridge rectifier ~ ~ : shorted
RP819 : 0.8 Ohms (meter probes resistance is about 0.7)

I suppose I have to unsolder MOSFET, check it again and check bridge rectifier too ?
And, if I replace MOSFET, I have to replace ICP801S (tda4863-2) again ?
I have a second one, but I have to buy a new MOSFET and/or bridge rectifier if needed.

Once you have removed the shorted fet, re-check the bridge rectifier, even with the fet is shorted (5.5Ω), you should not have a short between ~&~ of the bridge. If the bridge is shorted, ac is being applied to the pfc ciruit.

I have unsoldered the MOSFET.
PFC MOSFET : different values according to multimeter position :
103.4 K (multimeter set to 200K)
15.54K (multimeter set to 20K)
bridge rectifier + - : 5.2 Ohms
bridge rectifier ~ ~ : shorted
RP819 : 0.8 Ohms (meter probes resistance is about 0.7)

Looks like MOSFET isn't blown, but bridge rectifier is !
Do you know an equivalent of TS4B05G ? I have difficulties to find a replacement one (except from China, with really long delay).

[budm]

Re: Samsung LNS3251DA won't power on, no sound, no standby light-power board problem

Lift one end of RM801 then recheck the resistance of the bridge again.
What is the exact resistance reading between ~ and ~?