Samsung LN40B500P3F - Won't turn on

[veaux]

Re: Samsung LN40B500P3F - Won't turn on

With this box you pretty much put a bulb (the load) in serie with the TV which means that the voltage at TV will be less correct?

This box goes to the outlet and the tv is conected to the box right.

I'm curious (in the good way) to understand how this would affect the switching power supply in the TV if the TV gets a portion of the voltage it's expecting.

Do you happen to have a post somewhere in the forum explaining the why's? As mentioned earlier, I love to learn new things. Thank you.

[budm]

Re: Samsung LN40B500P3F - Won't turn on

"With this box you pretty much put a bulb (the load) in serie with the TV which means that the voltage at TV will be less correct?

This box goes to the outlet and the tv is connected to the box right."
That is correct, the cold resistance of the lamp will be very low (about 10X less than the hot resistance) about 15 Ohms for 100 W lamp (the current will be limited to about 0.8A if the circuit still have shorted circuit), so not much voltage will drop on the lamp so the power supply will still function but not at full capacity. if the circuit start drawing lots of the current then the filament will go up as the lamp gets brighter.
Best way to learn is to make one and experiment with it.

[veaux]

Re: Samsung LN40B500P3F - Won't turn on

Just put the card back on and ran the tests.

First of all without the wire harness to the logic board on to check the VSB and then after.

VSB was 5.3V without anything on.

I Then connected the harness and put the TV back on. I was happily welcomed with hte turn on sound of the TV. Apparently the TV turn back on and does not stay on std by that first time.

So:
Voltage at the main caps on Std by : 176V
Voltage at the main caps with TV on : 386V

I have a kill-a-Watt that was monitoring the connection (not very precise I guess but anyway). Stand by led On

Zero Amps pulled from the outlet on Stdby (certainly bellow the kill-a-watt specs)
0.33A and 38.3W when on.

I put a flash light to the screen and was able to see the "check cable no signal" message on the screen.

[budm]

Re: Samsung LN40B500P3F - Won't turn on

You are good to go to try the new MOSFETs.

[veaux]

Re: Samsung LN40B500P3F - Won't turn on

I just need to find them now... not well deserved in electronics shops in Monterrey,MX... I'll have to go through Mouser or Digikey and end up paying more for the shipping than the components themselves!

I think this will take a couple of weeks to put my hands on a pair of new MOSFETS. I'll post the final results.

thank you BudM

[veaux]

Re: Samsung LN40B500P3F - Won't turn on

Wuhu! I'm happy! I replaced the two MOSFETS and the TV is working like a charm!

I did my bulb box but I couldn't found a 100W incandescent bulb... tried with 70W but the TV went back stand by immedialety. So I tired direct and voila!

Posting a couple photos. TV Screen and Watt reading from the kill a watt.

Kudos to you budm, without your expertize I would't have been able to do it. It costed me 15bucks... And I still have 2 spare mosfets and some fuses! thank you!

[budm]

Re: Samsung LN40B500P3F - Won't turn on

Thanks for the good news and the follow-up on the repair.

[Mr.E]

Re: Samsung LN40B500P3F - Won't turn on

Hi, I think I am having either the same issue or a very similar issue to the ones mentioned in this thread. I have a Samsung LN40B500P3F with a BN44-00264A board. I got it for free from a family member, and they said occasionally it would just turn off. I plugged it in and left it running for 6 days and it seemed to work fine. The next time I went to turn it on, it would turn on for about 5 seconds and then turn off.

I have limited experience with this, with only having replaced obvious bulging caps on 2 different monitors, but i'm hoping to learn more and salvage this tv.

The only difference between my situation and the ones in this thread is that my fuse doesnt seem to be blowing. I think both cases in this thread has blown fuses.

I tested CI890 and CI891 and got the same results as post #19. I haven't tried testing them off of the board yet.

I didn't understand how to test the Mosfets in post 27, so i moved onto the next step(assuming that they may be bad such as in the case of veaux). I don't know which is the Gate, Drain, and Source.

I tested RI870, RI871, RI873, RI874, RI875, Ri876, RI878, RI879, and their values all matched veaux's in post 35. The only ones different were RI872=22.6k and RI877 = 22.7k. Does this mean they are damaged because they are below 30KF?

I checked CI892 and it showed .47uF, but i'm not sure how to check for leakage resistance.

On a final note, like an idiot I scratched the solder between RI871 and RI872 thinking it wasn't supposed to be there. I assume this is going to be a problem, am I able to bridge it back?

I appreciate any help that can be offered. I imagine the easy fix would be to just buy a new board. With shipping and everything to Canada I expect this to be around $130 CDN. I'm not sure I give the tv enough value to warrant that, so i'm hoping to fix it for cheaper.

Thanks for any help!

[veaux]

Re: Samsung LN40B500P3F - Won't turn on

Hi, if sometimes it turns on and some time it doesn't, your issue is not the same as mine.

Mine was a shorted MOSFET that consecuently blown the fuse.

Who know is the PS board is bad on yours.

[Mr.E]

Re: Samsung LN40B500P3F - Won't turn on

Hi, if sometimes it turns on and some time it doesn't, your issue is not the same as mine.

Mine was a shorted MOSFET that consecuently blown the fuse.

Who know is the PS board is bad on yours.

That makes sense.

So I just plugged the tv back in and it ran for 10 minutes before turning off, where as before it would turn off after 5 seconds. Any suggestions where I should start looking?

-Regards

[veaux]

Re: Samsung LN40B500P3F - Won't turn on

That makes sense.

So I just plugged the tv back in and it ran for 10 minutes before turning off, where as before it would turn off after 5 seconds. Any suggestions where I should start looking?

-Regards

When it runs off it is like you pressed the standby button on the remote or like the tv had no power at all?

[Mr.E]

Re: Samsung LN40B500P3F - Won't turn on

It turned itself off. I didn't touch anything.

Thanks

[tom66]

Re: Samsung LN40B500P3F - Won't turn on

By chance Mr. E, do you live in a country with 220-240V mains power?

[Mr.E]

Re: Samsung LN40B500P3F - Won't turn on

By chance Mr. E, do you live in a country with 220-240V mains power?

Canada, so 120v.

[Mr.E]

Re: Samsung LN40B500P3F - Won't turn on

Can someone please tell me how to test the STR - W6252. This seems to be a similar problem so I figure it's worth a look. https://www.badcaps.net/forum/showthread.php?t=15852 ?


Also, is the "bridge" that I scratched off between RI871 and RI872 fixable(mentioned in my previous post)?

Thanks

[budm]

Re: Samsung LN40B500P3F - Won't turn on

Can someone please tell me how to test the STR - W6252. This seems to be a similar problem so I figure it's worth a look. https://www.badcaps.net/forum/showthread.php?t=15852 ?


Also, is the "bridge" that I scratched off between RI871 and RI872 fixable(mentioned in my previous post)?

Thanks

OK, lets start with this first:
What DCV do you have on the connector CNM802 PIN3 (STB 5.3v), use chassis as the GND for your black meter probe.
Regarding to the connection of Ri870 and 871, the diagram shows that each end are connected together and that junction is also connected to the Emitter of transistor QI874 so it has junction with 3 components so you must be real careful connecting thing back the way it was other wise you will blow up that section. See page 2 of the diagram.

[Mr.E]

Re: Samsung LN40B500P3F - Won't turn on

Thanks Budm!

CNM802 PIN3 (STB 5.3v) = 5.21

Should i go ahead and try to repair that connection between Ri870 and 871 now incase I mangle it and have to get a new board anyways?


Correction: I just noticed the bridge is between 871 and 872, but I assume it makes no difference.

[Mr.E]

Re: Samsung LN40B500P3F - Won't turn on

I went ahead and repaired the bridge. If there's a way to test it I would like to do that, otherwise lets hope I didn't screw up!

[budm]

Re: Samsung LN40B500P3F - Won't turn on

Thanks Budm!

CNM802 PIN3 (STB 5.3v) = 5.21

Should i go ahead and try to repair that connection between Ri870 and 871 now incase I mangle it and have to get a new board anyways?


Correction: I just noticed the bridge is between 871 and 872, but I assume it makes no difference.

OK, the IC UM801S (STRW-6252) is fine, it is used for generating STB-5.3V, switched 13VS/M (this Voltage will be present when pin 1 ON/OFF (PS-ON, >2.5VDC) of CN802) will appear at the pins of connector CNM802.

Next you need to tell me if you do have 13VS on CNM802 or not, if it has then I need you to check the DCV measured between the two legs of the main filter cap CP815, it should be >360VDC.

[Mr.E]

Re: Samsung LN40B500P3F - Won't turn on

The readings are:
13VS on CNM802 = 12.46VDC
CP815 = 390VDC