Samsung LN32b460 No Backlights...have sound and picture

[allsmith]

Samsung LN32b460 No Backlights...have sound and picture


Hey guys long time since i've been on here...hope you all been doing good!..I had a good experience getting help from some of you all a few yrs ago that i really appreciated!!
But i've been busy with some other large projects and just haven't come across any tv's up until recent..

Here is what i got...

32" Samsung from 09 found in trash...Found blown main 6.3amp fuse on power board...Found the bridge rectifier(BD801s) was shorted along with a mosfet(QP802S)...
I have since replaced the fuse,the bridge rectifier and mosfet with similar spec'd ones i harvested out of other devices..Now they are not exactly spec'd and that could be a problem
and you guys can get on me about that first if you want!!.. but my plan was to at least make sure the panel was good then i'll order correct parts..also this tv is not a priority
or anything just a project for keeping me from getting bored..so im in no hurry and put me second inline for help,so you can help others that really need there tv's!

But anyways here is what i got now..

I have it hooked up to a 60 watt dim bulb tester and a gfci outlet...there appears to be no shorts as the bulb just barely glows...Plug in power and i get a red standby light and melody sound.
Power button and i get 5 flashes of the red light.
I have sound and video from a dvd player..picture confirmed with a bright flashlight.

I have also tested all diodes on top of the board.. lifted a leg on a few that i needed to,to test and none are shorted and seem to test normal with DMM diode test..I can get exact values if needed
Also i have replaced 3 small caps(47uf-50v) that i think could be start up caps at(CM804/CM808/CB804

Voltage on the large filter cap(CP815) is 168v with tv plugged in and in stand by...And 125v with tv turned on and playing a video..(Tested with DMM at both leads of cap)

Voltage test at(CNM802) using chassis as ground..
DET_5 = .428v at startup,drops to .359v for a few seconds,then back to .428 and stays steady, .052v tv off...(is DET_5 supossed to be 5v or .5v?? Im not sure.)
I-PWM = 0v
E-PWM = 3.89v..no change at start up...0v tv off
Inv_ON/OFF = 5v at startup,then drops to .039v,does that 4 times then stays steady at .039v
13v = 13.1v
13v = 13.1v
13v = 13.1v
5.3v = 5.1v
5.3v = 5.1v
5.3v = 5.1v
5.3v = 5.1v
13v = 13.1v
13v = 13.1v
STBY 5.3v = 5.1 no change at start up
H_Sync = 3.30v at startup,drops to 1.74v after a few seconds then stays steady at 1.74v
PWR-ON/OFF = 1.144v steady,no change at startup.. .038v tv off

Couple things i forgot..
Red standby light flashes 5 times when turning on then no light while tv is on
I did try to power up with main connecter(CNM802) unplugged from main board and nothing happens..( I read on a post on here of the same tv with different problems that its backlights
started when powering up power supply without main board connected)

Well i think thats it for now..hope i gave enough info to get started and can do any other testing that you need..just ask..
Im really not sure where to go from here,so any help would be greatly appreciated!!

Also i can get you part #'s of the components i changed and the ones i used for replacements..or even a link to the data sheet page if i can do that on here or not to save you time...Im not really good at telling whether or not a part can be used or not when theres slightly different specs! and since im trying to be cheap and refrain from ordering parts..you know,trying to get everything i need in one order and shipping charges and what not.
I did make sure the voltage spec was as high or higher..and i've tried two different mosfets at(GP802S)

Also i struggle at getting good pics,and hope what i took so far are good enough for you to see... if you need a better view at a certain board or area please just ask and i will..

Thanks guys...Lonny

[allsmith]

Re: Samsung LN32b460 No Backlights...have sound and picture

friendly bump...

I'm just a noob at this stuff so any help would be appreciated..
I was wondering if any of you guys can tell by looking at my voltages if the main board is sending the correct signals or not to the power supply,or if the problem is all in the power supply?..

[budm]

Re: Samsung LN32b460 No Backlights...have sound and picture

What dcv do you get between the two legs of the main filter cap when the TV is turned on, 400vdc?
Power supply/inverter board P/N BN44-?????

[allsmith]

Re: Samsung LN32b460 No Backlights...have sound and picture

What dcv do you get between the two legs of the main filter cap when the TV is turned on, 400vdc?
Power supply/inverter board P/N BN44-?????

Thanks for replying Bud..
I'm only getting 125vdc on the large cap's legs when the tv is on and playing a video.
168vdc when tv is off in standby
Power supply is BN44-00260A

[budm]

Re: Samsung LN32b460 No Backlights...have sound and picture

125Vdc? Are you sure?

[allsmith]

Re: Samsung LN32b460 No Backlights...have sound and picture

125Vdc? Are you sure?

I just checked again, Tv on, but no video playing this time i get 130vdc keep in mind it is hooked up to a dim bulb tester.

Without the dim bulb tester and plugged directly to gfci outlet i get 160vdc with tv on.

[CapLeaker]

Re: Samsung LN32b460 No Backlights...have sound and picture

Without the dim bulb tester, you should get 160 to 170V DC on the main filter cap without turning it on. When the TV is on, you should have closer to 400VDC. If the TV is on and you do not get at least 360V DC, the booster circuit in the primary isn't working.

[allsmith]

Re: Samsung LN32b460 No Backlights...have sound and picture

Without the dim bulb tester, you should get 160 to 170V DC on the main filter cap without turning it on. When the TV is on, you should have closer to 400VDC. If the TV is on and you do not get at least 360V DC, the booster circuit in the primary isn't working.

thanks yeah..it does have 168vdc when tv is off...
So the booster circuit is what i should be looking at?..any tips on what to check?.and a good noob question, can you show me roughly where the booster circuit is?

[budm]

Re: Samsung LN32b460 No Backlights...have sound and picture

Here is the diagram for the BN44-00260A.
Check and see if you do have VCC to run the PFC controller IC.
Check the 3 big black didoes D804, 805, 810 right by the main filter caps to see if any of them shorted out.

[CapLeaker]

Re: Samsung LN32b460 No Backlights...have sound and picture

thanks yeah..it does have 168vdc when tv is off...
So the booster circuit is what i should be looking at?..any tips on what to check?.and a good noob question, can you show me roughly where the booster circuit is?

And what is that voltage on the cap with the TV on? Does it come up or does it stay at 168V?

The PFC controller IC in the schematic that budm provided is UP801S (FAN7530) 8 pin IC.

[allsmith]

Re: Samsung LN32b460 No Backlights...have sound and picture

Here is the diagram for the BN44-00260A.
Check and see if you do have VCC to run the PFC controller IC.
Check the 3 big black didoes D804, 805, 810 right by the main filter caps to see if any of them shorted out.

Thank you Bud..
I have 67.5vdc on the VCC pin on the PFC controller IC at UP801S
I have checked the 3 big black diodes and none are shorted..And I did see the bulletin on those diodes causing start up problems..

[allsmith]

Re: Samsung LN32b460 No Backlights...have sound and picture

And what is that voltage on the cap with the TV on? Does it come up or does it stay at 168V?

The PFC controller IC in the schematic that budm provided is UP801S (FAN7530) 8 pin IC.

Thank you!
The voltage on the cap actually drops to 130V when the tv is on

[allsmith]

Re: Samsung LN32b460 No Backlights...have sound and picture

If you guys can look at the specs on the original mosfet at QP802s that was shorted (I see its in this PFC circuit) that i replaced with a used mosfet i found in a computer power supply just to make sure it will work in this application and that it is not what is causing my problem now since the specs are not quite the same. I actually have tried two different mosfets in this location with the same results..

Original Mosfet from tv...
http://www.datasheetlib.com/datashee...conductor.html

Tried this mosfet first from a computer power supply. Its voltage rating was higher but its resistance to open the drain was much different than the original...
http://www.datasheetspdf.com/PDF/F3NK80Z/650129/1

The mosfet that is installed now is out of a broken screen 37'' Samsung tv..it is 100V less than the original but i figured why not try it anyways and maybe i wouldn't have had to bother you guys..
http://www.datasheetspdf.com/PDF/K3561/625940/1

Also the bridge rectifier that i have in it now was used too,but its voltage rating was as high or higher than the original...but it looks like i got to pull the heatsink to get its part# to show you..If you think i should i can its not a problem...I just want to make sure the problem is not from me hacking in the wrong parts and running you guys on a wild goose chase and wasting your time..

Thanks guys!

[CapLeaker]

Re: Samsung LN32b460 No Backlights...have sound and picture

if the original mosfet was shorted to the gate, then you may have damaged gate drive components, maybe including the PFC IC. So check everything to be in spec in the gate drive circuit between the PFC IC and the gate of the mosfet.

The original mosfet was a 600V 10A, the second mosfet was a 800V 3A (too small), now you got an 500V 8A (also too small, but for testing purposes it should do).
The bridge rectifier should be good if it is rated as or better than the original.

check rp822, dp802, rp821, rp822, rp806 and LB803. Also see if RP820 or LB802 is open, DP805, LB805 and 806.

[allsmith]

Re: Samsung LN32b460 No Backlights...have sound and picture

if the original mosfet was shorted to the gate, then you may have damaged gate drive components, maybe including the PFC IC. So check everything to be in spec in the gate drive circuit between the PFC IC and the gate of the mosfet.

The original mosfet was a 600V 10A, the second mosfet was a 800V 3A (too small), now you got an 500V 8A (also too small, but for testing purposes it should do).
The bridge rectifier should be good if it is rated as or better than the original.

check rp822, dp802, rp821, rp822, rp806 and LB803. Also see if RP820 or LB802 is open, DP805, LB805 and 806.

Thank you for taking the time to look...I must have missed that second mosfet was only 3A,I dont remember it being that low..

Sorry for being so careless in trying to use parts i found laying around,but i was concerned that the panel of the tv could have been cracked and bad and hated to order parts..Im on a low budget,plus its just a little 32'' tv that was free and will be just used in my shop office so i wasnt too concerned about it..Now if it was a bigger tv and i knew more of its history i wouldn't be so careless. and yes if i get the tv working i will order the correct parts..Also i dont sell any of my fixed tv's i just use them or keep them for backups..

So yeah thats what i was hoping for that my parts could be used for test purposes. Now i will start looking into the components you listed for me and see if i can find any faults..thank you very much for your time!

[allsmith]

Re: Samsung LN32b460 No Backlights...have sound and picture

if the original mosfet was shorted to the gate, then you may have damaged gate drive components, maybe including the PFC IC. So check everything to be in spec in the gate drive circuit between the PFC IC and the gate of the mosfet.

The original mosfet was a 600V 10A, the second mosfet was a 800V 3A (too small), now you got an 500V 8A (also too small, but for testing purposes it should do).
The bridge rectifier should be good if it is rated as or better than the original.

check rp822, dp802, rp821, rp822, rp806 and LB803. Also see if RP820 or LB802 is open, DP805, LB805 and 806.

Testing done in circuit...
rp822=15.1 ohms
rp821=10.1 ohms
rp806=8.49 ohms
rp820=0.1 ohms

dp802= continuity both directions...diode test
dp805= fwd= .40v rev= open...diode test

lb803= 0.1 ohms
lb802=0.0 ohms
lb805=0.0 ohms
lb806=0.0 ohms

Can i ask..what are the ''LB'' components? transformer/transducer?

[allsmith]

Re: Samsung LN32b460 No Backlights...have sound and picture

Also guys i was curious if the 67.5vdc i get on the VCC pin on the PFC controller IC at UP801S is correct or not?

Although looking at the datasheet for the ICE3BR0665J PFC controller it states
10.5v - 25v operating range for VCC

I do see a discrepancy between the pin configuration of the PFC controller on the datasheet compared to the schematic Bud gave me. I checked the VCC voltage at pin 8 as described in the schematic and using chassis as ground.

Here is a side by side comparison picture of the pin configuration from the datasheet and the schematic

[cliff_hootarski]

Re: Samsung LN32b460 No Backlights...have sound and picture

PFC controller is on the "primary" side of the power supply, you must use the negative side of the main filter capacitor for your ground.

[CapLeaker]

Re: Samsung LN32b460 No Backlights...have sound and picture

google "FAN7530" and a pdf from mouser pops up. It has the same configuration as the schematic.

Look at the schematic at DP802. You can't measure that in circuit, because of RP822. So DP802 would have to be measured out of circuit. Other than that the gate drive components look good.

I think your voltage measurements are a bit off do to you are using the wrong ground as the poster above already mentioned, or the battery is flat in your DMM.

[budm]

Re: Samsung LN32b460 No Backlights...have sound and picture

Btw, you need to remove the inline Lamp or use 200W lamp, at only 130V at the two legs of the cap when TV is on the PFC may not start up due to low Voltage lock out.
BTW, how about D804, 805, 810? you did show the test result of all 3 diodes.