Samsung 2253BW - 2 Sec to Black issue

[AdamJ]

Hi all,

I recently purchased 2 faulty Samsung 2253BW monitor with the aim of fixing them both seeing as i successfully repaired my Samsung 19" TV. I've successfully repaired one of the 2253BW already by replacing the fuse (F301) and bad caps (C301 & C302) but i'm having trouble with the other one.

So far i've replaced:

C301 (820uf 25v)
C302 (820uf 25v)
C108 (820uf 25v)
C112 (820uf 25v)
C115 (1000uf 16v)
C116 (1000uf 16v)
C119 (330uf 10v)
C107 (47uf 50v)
F301 (125v 4a)

But still the screen comes on for 2 seconds and then off. Also, there is a high pitched noise which changes when the screen is switched off and on. Seems to be coming from around LF101 (near the power plug). Not sure if this is a red herring tho.

I know the screen panel is good as I've used a good power board on it and it displays fine.

Picture of the power board below:





Any suggestions welcomed.

Thanks for you replies in advanced.

Cheers
Adam

[budm]

Re: Samsung 2253BW - 2 Sec to Black issue

There are two SMD 8-PIN MOSFETs which drives the HV Inverter transformer, that section got very hot as you can see the board has burnt mark, you need to check them. Can you read the number as printed on top of the MOSFETs?

[AdamJ]

Re: Samsung 2253BW - 2 Sec to Black issue

Thanks, i think it reads "STM8309 81343"

Any idea how i would go about test that component ?

[budm]

Re: Samsung 2253BW - 2 Sec to Black issue

Need to look up the spec sheet to get the pin out of the Gate, Drian, and Source of the MOSFET so you check the resistance of those pins in combination.

S to D
S to G
G to D

[AdamJ]

Re: Samsung 2253BW - 2 Sec to Black issue

http://pdf1.alldatasheet.com/datashe...P/STM8309.html

Any idea of the range of read outs i should be seeing ?

S1 to D1 (both) - 341k
S2 to D2 (both) - 337k
S1 to G1 - 421k
S2 to G2 - 10k
G1 to D1 (both) - 0.815m
G2 to D2 (both) - 345k

[budm]

Re: Samsung 2253BW - 2 Sec to Black issue

They are not shorted out or has low Ohm readings, so looks OK.

[AdamJ]

Re: Samsung 2253BW - 2 Sec to Black issue

Actually, the only one that has a off reading compared to the others is the 2nd chip and S2 to G2, its reading is 5.7

Does that look like my problem ?

[budm]

Re: Samsung 2253BW - 2 Sec to Black issue

If it reads 5.7 Ohms, that is bad, and since you also had blown the fuse that feed the voltage to the MOSFETS something was shorted. You may want to check the fuse again.

[AdamJ]

Re: Samsung 2253BW - 2 Sec to Black issue

I'm trying to match up a replacement MOSFET but i'm not sure which one.... http://uk.rs-online.com/web/c/semico...ock=4294957913

I've filtered the required spec according to the spec sheet and got it down to 2, but which one ? Of course these might not be compatible.

Or these 2: http://uk.rs-online.com/web/c/semico...ock=4294957828

Cheers,
Adam

[budm]

Re: Samsung 2253BW - 2 Sec to Black issue

The pin out have to match.
Voltage and Current handling has to be the same or higher, not lower.
RdsON should be really close or lower, slightly higher will be OK (it will run hotter with higher RdsON). Vgs in the same range. Same or higher power dissipation.
DMC3028LSD is really close, it should work.

[AdamJ]

Re: Samsung 2253BW - 2 Sec to Black issue

I've managed to get a STM8309, its on its way.

Looks like its going to be very difficult to swap this out, its so tiny !

[Rtech]

Re: Samsung 2253BW - 2 Sec to Black issue

One thing to do,is to add solder,before unsoldering.

[wobbin]

Re: Samsung 2253BW - 2 Sec to Black issue

That's an easy swap really. RTech's suggestion of adding more solder first is a good one.

Cut he pins close to the chip with a sharp knife first. You only need to remove one pin at a time then and there's less chance of lifting a track with too much heat.

Tack each corner pin down of the new chip and then apply liquid no clean flux fluid and drag solder across the pins. If any pins are bridged with solder accidentally, simply apply more liquid flux and drag a clean soldering bit over the pins and the excess solder will come away. Or you can use solder wick to remove excess, whichever you find easiest.

HTH

[budm]

Re: Samsung 2253BW - 2 Sec to Black issue

I hope you order more than 1 MOSFET, I always replace both of them together.

[AdamJ]

Re: Samsung 2253BW - 2 Sec to Black issue

Thank you Badcaps !!! Its fixed and working !!

Special thanks to budm for his expert input and suggestions !

Cheers guys !