Samsung 460CXN - Power Supply Issue

[pantherts]

Hey everyone,

It's been a while since I've been here but I'm coming to you with another case to solve as I always turn to the Badcaps Forum to help diagnose these types of things. Alright let's get to it.

This Samsung 460CXN (has a built in Windows embedded PC in it) was found with a bad smell coming from it and no display; it was promptly unplugged and turned over to me for possible repair. Upon opening up the set and carefully inspecting the display's power board (this set has two power supplies, one for the display and one for the computer), I immediately noticed both Samwha HZ Series 450wv 150uF snap-in caps were leaking and bad. Electrolytic fluid had leaked onto the surface of the board and one of them was actually loose on it's legs. I've replaced both of these with brand new Nichicon GX Series 500v 150uF snap-in caps. The end result after quickly turning it on and back off was no power-on at all. We have quite a few of these things and when flipping the black power switch does not power on the display and computer side of things, there's usually an audible click from the main power board when it's receiving power. Just in case I tried shorting the display adapter's pin for power-on to see if I could force it and no-go there either.

I realize that for these guys to go it usually means something prior in circuit to them usually has gone bad thus allowing them to receive too much voltage. This display has been ran about 12 hours a day for the last 8 years or so, so age may have something to do with it as well.

Besides replacing the capactiors, I've removed and tested the ferrite diodes around this circuit which can be seen as having a checkmark by them in the pictures on the top of the board. I chose to do this because there was some discoloration around their solder joints and they must have gotten hot. Another thing to note is the noticeable black squigly mark on the top of the board near the transformer; not sure what that is. And then I noticed a bit of residue or an abnormality around one of RL811S on bottom view of board.

Please take a look at the attached pictures and let me know if you all see anything that I should be testing here or that you'd like to take a closer look at.

Thanks as always!

[budm]

Re: Samsung 460CXN - Power Supply Issue

https://www.badcaps.net/forum/attach...5&d=1524081045
You need to report the Volatges of all the pin on the power board that goes to main board, as you can see, the pins are labeled so you must report the reading so we can easily identify the pin name and its Voltage.
Pin 1 NAME, 'VOLTAGE reading'
Pin2 """"""""""""""""""""""""""""""

BTW, that display power supply board P/N is BN44-??????
So did you re-solder those bad joints on those diode and any where else that look bad?
https://www.badcaps.net/forum/attach...0&d=1524081045

[pantherts]

Re: Samsung 460CXN - Power Supply Issue

Thanks for the quick reply Bud! Here's that info you requested:

All pins leading to the main display board are not receiving any voltage whatsoever. I tested the power switch leading onto the board and verified that is indeed working. Whatever is going on here, there's no power making it past the initial power circuit of this thing.

(Saving this listing for later if I need it as I had already typed it up)
Pin 1 (Power On/Off):
Pin 2 (Sync.):
Pin 3 (STB5.2V):
Pins 4-6 (GND):
Pins 7-8 (12V):
Pins 9-12 (GND):
Pins 13-16 (5.4V):
Pins 17,18 (GND):
Pin 19 (13V):
Pin 20 (GND):
Pins 21-22 (13V):
Pin 23 (On/Off):
Pin 24 (NC):
Pin 25 (EPWM):
Pin 26 (GND):
Pin 27 (DET_5V):
Pins 28-30 (NC):

Information for the model number of this power supply is in image attached. I have un-soldered and removed each of the diodes in the initial power supply circuit (found around the large caps), tested them and then re-soldered them in. Each of the ones with a black checkmark next to them in marker on the top board shot.

Thanks as always!

[pantherts]

Re: Samsung 460CXN - Power Supply Issue

New development while working at getting this thing connected out of the case so I could test voltages on the bottom of the board. I believe the very first fuse on the board is blown. Are these ceramic fuses? I thought they were supposed to actually break when bad? Removing fuse for testing now.

[R_J]

Re: Samsung 460CXN - Power Supply Issue

If it is the main fuse on the a/c line in, check QP801s and QP802s to make sure they are ok and not shorted

If you have no 5.2 standby voltage, check FM802 fuse, If it is bad, UB801s (ic) could be bad, shorted.

[pantherts]

Re: Samsung 460CXN - Power Supply Issue

Both fuses on the L and N lines were bad coming into the board as well as the fuse on the computer's power supply as I assume it blew when the other two blew. Quite a few bad fuses here. Working on finding some replacements. In the meantime I swapped some around and tested voltages. QP801s and QP802s are these (http://www.datasheetcafe.com/sd20n60...heet-infineon/). Not sure if I'm going to be able to test those with this crappy multimeter I have here.

As far as UB801s is concerned, it's a https://cdn.badcaps-static.com/pdfs/...d718dc5d57.pdf Green Mode Fairchild Power Switch. I've replaced the fuses leading up to it and I'm reading ~114V on every single pin on this thing, so I'm guessing that's probably not correct.

I feel like I've made some progress here as power is now flowing almost completely through this power board but it's still not making it to the main pin outs at all.

Anywhere else you'd like me to test voltages to verify we have the proper current coming into and out of certain places?

Thanks!

EDIT: Also, this entire board as Budm asked earlier and I just now came across in research is a Samsung BN44-00166F Power Supply / Backlight Inverter.

[R_J]

Re: Samsung 460CXN - Power Supply Issue

When measuring voltages in the primary or HOT side, DO NOT use the chassis as ground, use the (-) leg of the main filter CP810/CP817. UB801s should have at least 160v on pins 6,7,8. pin one will be (hot) ground, pin 2 will have around 15-18 volts
As for QP801 & QP802, just make sure they are no shorts between the leads.

[pantherts]

Re: Samsung 460CXN - Power Supply Issue

Got it. Okay.........soooooo I think I inadvertently found the issue. Kept blowing fuses on the L and N and just had NT811S pretty much explode, so that was fun. Suffice to say I may have more issues than I originally thought now. *Sigh*

Really looking at that RL811S module right now as it's the one that had some funny discoloration around the pads on the bottom of the board.

Any ideas as to where to go from here? :-\

Edit: Also, I do think there's an issue with QP802. Measuring it's resistance between Drain and Gate is all zero. QP801 reads out at 200ohms Drain to Gate.

[R_J]

Re: Samsung 460CXN - Power Supply Issue

If nt811s blew, then you have a dead short. Check the bridge rectifier, check the resistance between the + and - of the bridge (or across CP810)

normally that ntc thermistor will get shorted (bypassed) by the relay RL811s but the power supply standby voltage needs to be working to energize the relay.
If fuse FM801 and FM802 are good, then you have a shorted component in the pfc circuit.

[pantherts]

Re: Samsung 460CXN - Power Supply Issue

God I was looking for that schematic everywhere. Thanks so much for supplying that! Alright, so you're talking about the bridge rectifier at BD801S then I'm guessing. That makes absolute sense about the relay RL811S not kicking in without the standby voltage working; I can see the traces heading right on over there that would connect it to all that.

BD801S resistance from + to - is a whopping 0.4Ohms. Checking continuity confirms there's a short here between these two. This BR is toast eh?

Edit: I'm surprised that thing thing was even working temporarily after I replaced the caps and the fuses. But then the fuses kept blowing, so instead I used some thin wire for the N and L fuses which pretty much seemed to narrow down the issues here. I likely caused more issues but it may have pinpointed the issue? Not sure if that was the smartest thing but I was going through fuses like they were going out of style here.

[R_J]

Re: Samsung 460CXN - Power Supply Issue

Most likely, but remove it and check it out of circuit to be sure, if it checks o.k. you could still have a shorted part elsewere.

[pantherts]

Re: Samsung 460CXN - Power Supply Issue

Hmm, okay I've removed it and check the resistance between the + and - now completely out of circuit and I'm showing no resistance whatsoever now. I carried on with testing it using Diode check and did the back and forth swapping leads test across it. Readings are only one way:

From Left to Right Testing:
+ to AC = OL
AC to + = 0.460
AC(pos lead) to AC(neg lead) = OL
AC(neg lead) to AC(pos lead) = OL
AC to - = OL
- to AC = 0.466

- to + Resistance is 143 on 200k resolution

If I'm not mistaken then this thing may be okay?

[R_J]

Re: Samsung 460CXN - Power Supply Issue

That correct, they are usually tougher then other parts. Now check across the + & - on the board, you should still show a short.
My money is on shorted fets, if they are shorted, check the rp824/rp811 resistors (10 ohm) and the dp801/dp805 diodes.

[pantherts]

Re: Samsung 460CXN - Power Supply Issue

Yep, there's continuity there.

[pantherts]

Re: Samsung 460CXN - Power Supply Issue

I'm going to have to run for the night, as I have to pick up the g/f. But I'll check back in when I'm home.

Also, as far as NT811S goes, the only spare thermistor I have on hand is a SCK 2R58 (going to have to place an order anyways with digikey so I'll have to add some parts to the list), but I'm not sure what the original part on this board was since it self disintegrated and took some of my vision with it.

[R_J]

Re: Samsung 460CXN - Power Supply Issue

It is 8 ohm, should be a SCK-084 or SCK13-084 You could use the one you have to test the board, then I would install the correct one later.

[pantherts]

Re: Samsung 460CXN - Power Supply Issue

R_J,

Thanks! I'll add that to the list to order then, along with more fuses. So what do you think is shorting out after this bridge rectifier?

Edit: Just saw your earlier post with the things to check. I'll check out the two mosfets closer and rp824/rp811 resistors (10 ohm) and the dp801/dp805 diodes. I do think QP802 has an issue though already. Measuring it's resistance in circuit between Drain and Gate is all zero. QP801 reads out at 200ohms Drain to Gate.

[pantherts]

Re: Samsung 460CXN - Power Supply Issue

So I've removed the QP802S mosfet from the board and confirmed it to be totally shot. Conductivity on every leg to every leg. Now when I test for conductivity between the positive and negative pads where the bridge rectifier are I have an OL. BUT, when I take a wire and stick it into where QP802S Source and Drain pads are I'm seeing conductivity again. Somehow I don't think this is okay.

I've tested the RP824 and RP811 resistors and found them to be spot on at 10ohms each. Correction: DP801 is fine. Still checking DP805.

QP801S is still in-circuit and seemingly is working okay. No conductivity between gate and source or drain.

Alright, hopefully that covers it where I'm at.

[R_J]

Re: Samsung 460CXN - Power Supply Issue

What do you mean "when I take a wire and stick it into where QP802S Source and Drain pads are I'm seeing conductivity again"
are you placing a wire between source and drain pads?? of course that would show a short. The source IS HOT ground and placing a wire from drain to ground would show a short.
with QP802 REMOVED what is the resistance between source and drain pads where QP802s was (no wires please)

[pantherts]

Re: Samsung 460CXN - Power Supply Issue

I guess I was under the impression that power flowed from source to drain and then was amplified by the gate activating? I think I was confused trying to follow the positive and negative coming off the BR. I thought we were trying to get it so the BR positive and negative terminals were not showing a short between the two.

Edit: Sigh, Okay so I see now looking at the other mosfet that those two do not have conductivity between them. I guess I was confused as to how a power mosfet actually functions.