samsung LN-S4051D diagnal lines

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

been checking these ics, the readings seem funny, ic101 from top=1.79v left=2.8mv right=3.34v. ic102 top=2.7mv left=13.3v right=7.9v. ic1702 top=starts at 22 mv keeps going up, left=3.7mv right=5.09v, middle=2.5v, which I thought the middle should equal the top, seems like one or all of these are messed up, thinking this might be causing my snowy picture, any ideas?, thanks.

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

well this one crapped out again, getting the clicking of the relay every 5 seconds, fixed it once with electro caps replacement and reflow of solder joints, lasted a few months now its back same thing, clicks every 5 seconds. When powerboard is unhooked from mainboard clicking stops but backlights don't come on, when heating area of ics801 for a minute or two tv comes on for 15 minutes or so no clicking, replaced or checked all caps and resistors in that area, anyone know if heating ics801 is making it work for that 15 minutes or should heating it have no effect on the ic as in letting the tv work for that 15 minutes??: sj pic of powerboard: https://www.shopjimmy.com/samsung-bn...ight-inverter/

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

seem to have a strange reading on bridge rectifier, when tv backlight is on the dc voltage on the outer 2 pins are 106 volts, where I think it should be around 160, all diodes of bridge rec. read correct and inner 2 legs are 120 ac as expected, any thoughts on why the voltage is low?

[lotas]

Re: samsung LN-S4051D diagnal lines

PFC (Power Factor Correction) does not work.

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

Thanks Lotas.

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

think i found a bad mosfet, QI802, read funny, took it out, getting 192 ohms from drain to source, isn't that way too low?

[lotas]

Re: samsung LN-S4051D diagnal lines

think i found a bad mosfet, QI802, read funny, took it out, getting 192 ohms from drain to source, isn't that way too low?

Discharge its mosfet (short all three legs with a metal object) and check again with a multimeter.

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

ok, shorted all 3 legs, it's 197 ohms drain to source.

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

I think I messed something up earlier, I was trying to test voltages on that mosfet with tv on, had a probe on neg. of bridge rec. and when I touched drain or source it was one of them, then the backlights went out, now they won't come back on even after heating that small section like before, but the damn thing did quit clicking every 5 seconds.

[lotas]

Re: samsung LN-S4051D diagnal lines

Well, if the mosfet has broken, you need to check all nearby components for breaks and short circuits (resistors, diodes, zener diodes ...). After that, you can install a new mosfet.

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

Think I'm on the wrong path, just tested a couple more on a different powerboard, from a different brand and size tv, one was 176 ohms, the other was 90 ohms.

[lotas]

Re: samsung LN-S4051D diagnal lines

The mosfet should not have low resistance between the drain and the source (if a diode and a zener diode are built into them), then a multimeter will show a working mosfet as you check a regular diode.

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

ok, I ran some leads out from the main filter cap, there's 171 in standby and 381 when powered on, no backlight and the relay clicking is back, clicks 2 times every 5 seconds.

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

no progress going in reverse lol, tried testing voltages with tv on, there's no backlight now, voltages at cnm 801 conector are right on and solid, had 381 0n main cap, was testing voltages on ics801, neg. of main cap for ground, when i touched pin 5 or 6 tv would go off and come back on, could tell by the samsung chime, pin 7 had 14.35, I think thats just a bit low, then was checking icp801 and while checking one of the pins tv went off. checked to see if main cap was still 381 but was only 165 in both stby and powered on, the led on optical out blinks once then is out, led on front behaves like it should solid red for stby and off when powered on.

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

clicking 2 times every 5 seconds is gone again, think I either blew something while testing those ic voltages, which doesnt seem like it should have or maybe one of them is bad, maybe a resistor or a bad solder, not sure.

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

I think maybe icp801 is bad, it is the pfc controller: https://cdn.badcaps-static.com/pdfs/...43ef79150d.pdf

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

found 2 tiny resistors on underside of powerboard 75r0 and 82r0 close to cni804 connector both read 39.5 ohms, think those could be causing these problems?

[lotas]

Re: samsung LN-S4051D diagnal lines

found 2 tiny resistors on underside of powerboard 75r0 and 82r0 close to cni804 connector both read 39.5 ohms, think those could be causing these problems?

If these two resistors (75Om and 82Om) are connected in parallel, then you get just 39.2Om.

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

ok, thanks Lotas, I'm glad those little buggers are alright.

[nomoresonys]

Re: samsung LN-S4051D diagnal lines

seem to have a short somewhere that I can't find, dim bulb tester stays lit.