Samsung 2343nw no power

[speedraver]

Hi everyone.

I'm a newbie with electronics (I've succesfully repaired 2-3 monitors using youtube/topics here and a solder iron + some new caps/fuses), but now I've stumbled upon one where the problem isn't as obvious as a blown cap:

I've received this Samsung 2343nw monitor from a friend, with the only explanation: "It doesn't turn on anymore".

After some basic testing (try other powercable, check settings/manual for possible software problems with power save mode etc), I've opened up everything and did a quick visual inspection of the power pcb (see attached pictures below).

Observations:
- no visual damage to capacitors etc.
- little bit of charring on the bottom of what seems to be a very basic inductor coil (circled in red in the pictures, only identification I could find was the nr LF101 written on the pcb)

Tools I currently have
- very old multimeter with some basic A/V/ohm measurements (currently looking to upgrade to something like an extech ex330)
- solder iron and supply

My questions
- can somebody identify this specific coil and point me in the right direction to find a replacement (if this is even possible)?
- are there any diagnostics I can try without other specialized equipment (an ESR/CLR meter seems to be the go to tool for this kind of stuff, but I'm not sure if €100-ish is worth it at the moment to use it maybe once or twice a year)?
- any other things I might overlook/try first as a newbie?

Thx in advance.

[budm]

Re: Samsung 2343nw no power

That is a just an AC line filter, are the wires burnt? Do you get resistance < 1 Ohm between the white and Black wires? It looks like it has bad solder joints so it over heated.
The main AC fuse (red cylinder) is OK? Do you get about 330VDC between the two legs of the main filter cap.
BTW, that line filter can be bypassed for testing the rest of the circuits.

[speedraver]

Re: Samsung 2343nw no power

That is a just an AC line filter, are the wires burnt? Do you get resistance < 1 Ohm between the white and Black wires? It looks like it has bad solder joints so it over heated.
The main AC fuse (red cylinder) is OK? Do you get about 330VDC between the two legs of the main filter cap.
BTW, that line filter can be bypassed for testing the rest of the circuits.

Thx for the quick reply!

Wires itself seems fine (no burnmarks or molten insulation).

Ohm measurement Line filter:
- white to black = nothing (of course)
- white/white and black/black = <1 Ohm (partly guessing, the multimeter I'm using is quite crappy)
=> it seems this one is still ok?


Main AC fuse (red cylinder that has the same form as a capacitor):
- upon closer inspection, there is some light charring on the pcb around the fuse
- after testing resistance -> 0 Ohm, no reaction whatsoever
=> I'm guessing I'll need to get at least a new fuse. It's labelled T 3.15A 250V 2000 -> I'm guessing any fuse with 3.15A and 250V or (a little bit) higher will do?

Main filter cap
- I presume this is the biggest cap on the board? (spot the newbie :p )
- I'm measuring resistance (>1Ohm), so I can assume it's working
- I haven't tested the DCV yet, because I don't think it will charge with a broken fuse and I'm not sure whether it's a good idea to try to charge the cap with a battery if it's still soldered to the board.

[budm]

Re: Samsung 2343nw no power

Thx for the quick reply!

Wires itself seems fine (no burnmarks or molten insulation).

Ohm measurement Line filter:
- white to black = nothing (of course)
- white/white and black/black = <1 Ohm (partly guessing, the multimeter I'm using is quite crappy)
=> it seems this one is still ok?


Main AC fuse (red cylinder that has the same form as a capacitor):
- upon closer inspection, there is some light charring on the pcb around the fuse
- after testing resistance -> 0 Ohm, no reaction whatsoever
=> I'm guessing I'll need to get at least a new fuse. It's labelled T 3.15A 250V 2000 -> I'm guessing any fuse with 3.15A and 250V or (a little bit) higher will do?

Main filter cap
- I presume this is the biggest cap on the board? (spot the newbie :p )
- I'm measuring resistance (>1Ohm), so I can assume it's working
- I haven't tested the DCV yet, because I don't think it will charge with a broken fuse and I'm not sure whether it's a good idea to try to charge the cap with a battery if it's still soldered to the board.

You have shorts circuit so the main AC blew.
- I'm measuring resistance (>1Ohm), so I can assume it's working That should be the 1000's Ohm range. You need to check the rectifier diodes, power MOSFET'S, etc. for low resistance readings first other you will waste the good fuse (Fuse is Time Delayed (SLO-BLO) type, not fast blow.

[speedraver]

Re: Samsung 2343nw no power

You have shorts circuit so the main AC blew.
- I'm measuring resistance (>1Ohm), so I can assume it's working That should be the 1000's Ohm range. You need to check the rectifier diodes, power MOSFET'S, etc. for low resistance readings first other you will waste the good fuse (Fuse is Time Delayed (SLO-BLO) type, not fast blow.

Will do

But to clarify: the meter I'm using is really shitty (it's an old analog one, so I have to half guess the reading from the pointer after manually calibrating the zero point -> really long overdue for an update :p ). That's why I only said > 1 Ohm (as is: there is resistance, it ain't completely broken)

Just tried it again, this time al little more refined:
- on setting 1k (I presume 1000's, since manual doesn't specify further), it get a reading of 3-5.

So with this extra info: should I risk trying another fuse, or is it time to invest in better material to diagnose stuff further (and I'm guessing not only a better multimeter)?

[budm]

Re: Samsung 2343nw no power

I get better meter first since wrong measurement info can throw off troubleshooting.

[speedraver]

Re: Samsung 2343nw no power

I get better meter first since wrong measurement info can throw off troubleshooting.

Alright, any recommendations (I'm currently looking at the Extech EX330, is it worth the €60 compared to a basis non-autorange device like a Uni-t ut132)? Any other tools that I definitely will need for this kind of repairs?
Also: any other things I can try in the meantime? (I can measure if parts are completely broken = no current/resistance/... measurement whatsoever)

Thx again

[speedraver]

Re: Samsung 2343nw no power

I get better meter first since wrong measurement info can throw off troubleshooting.

Looked around a little bit more, and it seems the Extech is limited to 200uF, which seems rattle low for LCD-repairs.

I've found the Uni-T139C that ranges to 99mF (and is only $35 at the moment). It has its limits ofcourse (6000counts), but it seems decent enough for its price.

Is there a general topic to ask this kind of buying advice (I've looked around, but could really find one)?

[budm]

Re: Samsung 2343nw no power

I hope retiredcaps will chime in.

[speedraver]

Re: Samsung 2343nw no power

Ok, finally updated my multimeter and found the time to do some detailed troubleshooting (I hope it's ok to bump this thread).

That is a just an AC line filter, are the wires burnt? Do you get resistance < 1 Ohm between the white and Black wires? It looks like it has bad solder joints so it over heated.
The main AC fuse (red cylinder) is OK? Do you get about 330VDC between the two legs of the main filter cap.
BTW, that line filter can be bypassed for testing the rest of the circuits.

More detailed measurements (in circuit):

• AC line filter: 2,5M Ohm
• AC fuse: blown (and have replacements available)
• Main Filter Cap: 110uF (labelled 120uF, so within margins). I can do a VDC test, but I'm not sure this can be done in circuit and I rather don't start desoldering if not necessary

You have shorts circuit so the main AC blew.
- I'm measuring resistance (>1Ohm), so I can assume it's working That should be the 1000's Ohm range. You need to check the rectifier diodes, power MOSFET'S, etc. for low resistance readings first other you will waste the good fuse (Fuse is Time Delayed (SLO-BLO) type, not fast blow.

Next on my list to get to, can I measure these in circuit?

[budm]

Re: Samsung 2343nw no power

'AC line filter: 2,5M Ohm' 2.5 million Ohms? You need to clean and resolder all four pins and then take the reading again.

'Main Filter Cap: 110uF (labelled 120uF, so within margins). I can do a VDC test, but I'm not sure this can be done in circuit and I rather don't start desoldering if not necessary'
You need to measure the DCV with the cap still in the circuit.

[speedraver]

Re: Samsung 2343nw no power

'AC line filter: 2,5M Ohm' 2.5 million Ohms? You need to clean and resolder all four pins and then take the reading again.

'Main Filter Cap: 110uF (labelled 120uF, so within margins). I can do a VDC test, but I'm not sure this can be done in circuit and I rather don't start desoldering if not necessary'
You need to measure the DCV with the cap still in the circuit.

AC: yep, 2,5 million Ohms, I'll guess I'll heat up my solder iron...

MFC: Can I use something like a 9V battery to charge it (when in circuit) or do I have to connect the power supply (fuse is blown + rather try to avoid working on circuits just after connecting them to AC if not necessary)

(I prolly look like a complete noob, but I rather ask a stupid question than take a stupid risk)

[budm]

Re: Samsung 2343nw no power

OK, I forgot that you have shorts circuit some where on the board.
So did you do the resistance testing on the bridge rectifier, MOSFET, etc. as suggested?

[speedraver]

Re: Samsung 2343nw no power

OK, I forgot that you have shorts circuit some where on the board.
So did you do the resistance testing on the bridge rectifier, MOSFET, etc. as suggested?

Measured on AC side of power supply(in circuit)
- bridge rectifier in diode mode: 0.548, 0.556, 0.482V
- other diodes: 0.3-0.7V
-caps: all in 100k or MOhm range, F-values within margins (1 fluke with a 47uF one, but prolly because measured in circuit)

What's left on AC side:
- mosfet: none on ac side, 2 on dc I'll have to lookup
- AC/DC Converters Off-Line Switcher, of which I have no idea how to measure it.
- spool
- transfo
- Transistor Output Optocoupler

Next up: desolder line filter

Any thoughts?

[budm]

Re: Samsung 2343nw no power

https://www.badcaps.net/forum/attach...0&d=1450194111
OK, it uses SMPS IC mounted on the heatsink to the right of the bridge rectifier, that IC is the main switching power supply that drives the main power transformer.
Get the P/N to get the pinout.

[budm]

Re: Samsung 2343nw no power

BTW, when you test resistance of the line filter, you check between pin 1 & 2, pin 3 & 4 resistance, right?

[speedraver]

Re: Samsung 2343nw no power

BTW, when you test resistance of the line filter, you check between pin 1 & 2, pin 3 & 4 resistance, right?

Did it both ways...
When I measure 1,2 & 3,4 I get 0,1-0,2 Ohm

Lucky I didn't start soldering yet.

[speedraver]

Re: Samsung 2343nw no power

https://www.badcaps.net/forum/attach...0&d=1450194111
OK, it uses SMPS IC mounted on the heatsink to the right of the bridge rectifier, that IC is the main switching power supply that drives the main power transformer.
Get the P/N to get the pinout.

P/N: J820 TOP257YN 54439B -> Link in my previous post pointed to the manufacturer, which has the following datasheet: TOP257YN

-> So I know the source and drain (.OL as expected), but I'm not sure which one(s) act like a gate? (I understand the basic working of a mosfet, but this is a little more complex).

(btw, thx again for the quick help!)