Samsung 23" LCD P2350 Inverter Repair

[majkstone]

Re: Samsung 23" LCD P2350 Inverter Repair

Update on the board
trafo desoldered and mesuring resistance 9s1-s2=960ohm s3-s4=1080ohm
i have 13V 5V and 3.3V from inverter board here no problem.
mosfets 4512 SMD 8pin try to test on board they are not in short but diff to check without desoldering (by measuring seem both ok also not overheating)

I am shure i have problem with feedback current to the main IC1 chip from CFL lamps to IS (pin4) and FB and VS pin 3 and 5
i am trying to cheat the U101 BD9893F adding resistor in serial with the trace to IS?
Same to do with trace to COMP (pin9)
using this sch of BN44-00296 but my board is BN44-00297D
Anyone have the inverter sch of the BN44-00297D please post will help alot.

https://www.badcaps.net/forum/images...frantic4yc.gif

[adamelec]

Re: Samsung 23" LCD P2350 Inverter Repair

I also have the same inverter board, I think someone did a 500V insulation resistance test on the screen an blew it up.

I have tested all fuses. There is 13V on Pin 2, but nothing on the 5V pin 5/6 or the 3.3V pin.

I put the scope across Drain and GND of the SMPS IC (U101) and am only getting switching bursts 500ms apart. I assume this is the low power mode of the chip. Should the chip be in standby mode or is there something wrong here?

[Dzevo]

Re: Samsung 23" LCD P2350 Inverter Repair

Hawe same inverter board, like others stay on for 2 sec than go off
changed all the caps
trafo look s ok
mosfets 4512 to be chacked
interested how to forced to sw on the inverter only by ext 3v on pin8 on/off

[selldoor]

Re: Samsung 23" LCD P2350 Inverter Repair

Really pleased for you- still think getting the dual mosfets would have been easier, but you have proved that it can be done. Thanks also for posting the diagram to help others - I have not checked it so hope it is correct..

[CroTech]

Re: Samsung 23" LCD P2350 Inverter Repair

I`ve finally fixed it

I should have looked at the datasheets first and look for the pinouts of the ICs and I would have seen what was the problem...

The big replacement MOSFETs work just fine if they are soldered in the right places.

Here is the picture where I made a mistake.
I soldered the first MOSFETS gate to the wrong solder point.
I have soldered it to the first solder point but it should have been soldered to the point right next to it.

[CroTech]

Re: Samsung 23" LCD P2350 Inverter Repair

so you both suggest buying an original replacement MOSFET since this fix is not a 100%?

[selldoor]

Re: Samsung 23" LCD P2350 Inverter Repair

I have been away for a week but see no progress?

I did wonder why you went for this conversion option it does look very messy and the OP had only one post and never even commented after.
Can we be sure it really worked? It is also difficult in the pictures to tell exactly what the connections are.

A fellow Zagrebian? has just replaced his mosfets and seemed to just pop out to the electronics store and bought his. Perhaps PM him and ask where he shops?
https://www.badcaps.net/forum/showthread.php?t=25926

Whilst not the same set and not the same mosfets I think they would be a good sub.

Perhaps Budm can confirm or refute.

SUGGESTED SUB - Available in Zagreb
http://html.alldatasheet.com/html-pd...1/STM8309.html

ORIGINAL 4512C
http://pdf1.alldatasheet.com/datashe...AF4512CSA.html

[budm]

Re: Samsung 23" LCD P2350 Inverter Repair

1. MOSFET (irf540n) - Gate 0, Drain 0.08, Source 0
2. MOSFET - Gate 15.98, Drain 0.05 Source 16,13
3. MOSFET - Gate 0, Drain 0, Source 0
4. MOSFET - Gate 15.96, Drain 0, Source 16,11

All was measured in 20V range... AC was pluged in and LEDs were ON!

EDIT: Checked for shorts using continuity.
The first MOSFET has source and gate shorted but I assume that´s OK since
it was solder on the same point like in post#1
Only the first one is shorted like that, and when desoldered there are no shorts.

Source and Gate should never be tied together period, if that is the case, it will be completely wrong and will never work.

[CroTech]

Re: Samsung 23" LCD P2350 Inverter Repair

bump

[CroTech]

Re: Samsung 23" LCD P2350 Inverter Repair

anyone?

[CroTech]

Re: Samsung 23" LCD P2350 Inverter Repair

1. MOSFET (irf540n) - Gate 0, Drain 0.08, Source 0
2. MOSFET - Gate 15.98, Drain 0.05 Source 16,13
3. MOSFET - Gate 0, Drain 0, Source 0
4. MOSFET - Gate 15.96, Drain 0, Source 16,11

All was measured in 20V range... AC was pluged in and LEDs were ON!

EDIT: Checked for shorts using continuity.
The first MOSFET has source and gate shorted but I assume that´s OK since
it was solder on the same point like in post#1
Only the first one is shorted like that, and when desoldered there are no shorts.

[CroTech]

Re: Samsung 23" LCD P2350 Inverter Repair

sorry, I`ve been busy stuyding for the finals... I`ll get those readings tomorrow since it is late now and I still have a lot of studying to do... Thanks in advance

[budm]

Re: Samsung 23" LCD P2350 Inverter Repair

"I read that any shorts with the gate indicates a faulty MOSFET" You should check S-G,D-G, S-D.
By the way, if they checked out OK, put them back in and give me the DC voltage reading between the ground and the metal tab of each MOSFETS.

[Rtech]

Re: Samsung 23" LCD P2350 Inverter Repair

Lots of reasons for the '2 secs to Black' you have...no easy answers unfortunately,just follow the procedure as described in the 'sticky',and hope.

[jeranio]

Re: Samsung 23" LCD P2350 Inverter Repair

I have the same problem. Samsung P2350 shuts of backlight after 2 seconds. After reading this entire post, I am not sure which direction to head. Waiting to see if anyone figures out the real reason why backlights switch off. I know without having a complete working module to swap and check this can be daunting fault to find but by now there are have been millions of these made and somebody out there knows a definite way to pinpoint the faulty components with some easy checks.

[CroTech]

Re: Samsung 23" LCD P2350 Inverter Repair

Is there anything else, any ideas? :/
Could it be the mains cap (the big one)?

[CroTech]

Re: Samsung 23" LCD P2350 Inverter Repair

I tested the MOSFETs by checking for shorts and using diode check...
I read that any shorts with the gate indicates a faulty MOSFET, so I assume they are ok, since none of them is shorted.

Also you can hear high pitched noise after the backlight shuts down.

[selldoor]

Re: Samsung 23" LCD P2350 Inverter Repair

Hmm thought I asked if you had anything else to test the panel on in post 68.

Have you re tested your Mosfets since fitting them?

[CroTech]

Re: Samsung 23" LCD P2350 Inverter Repair

CCFLs are fine, brightness is good and it is working fine when connected to the 940n power board, I left it for a few minutes and worked just nice... No redish color indicating dying lamps

[CroTech]

Re: Samsung 23" LCD P2350 Inverter Repair

Well than I am going to try that...