Samsung Syncmaster 204B repair

[sermulis]

Hello,

I just received monitor for repair with missing components in power supply board.
So, at first I should identify what should be installed in missing places before i test the monitor.

I was able to find that on C105 should be 150uF 450V capacitor, but was not able to find right capacities/voltage parameters for C110, C111, C112, C113, C304, C305 and some component missing in C102.

Could please someone who is familiar with this board IP-43130B, help me out what should be installed in missing places?

Thank you in advance.



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[lexwalker]

Re: Samsung Syncmaster 204B repair

I just received monitor for repair with missing components in power supply board.
So, at first I should identify what should be installed in missing places before i test the monitor.

I was able to find that on C105 should be 150uF 450V capacitor, but was not able to find right capacities/voltage parameters for C110, C111, C112, C113, C304, C305 and some component missing in C102.

Could please someone who is familiar with this board IP-43130B, help me out what should be installed in missing places?

Let's see...

C110, C111 - 820uF 25V or 1000uF 25VC
C112 -> 330uF 25V or 470uF 25V
C304, C305 -> 470uF 25V or 680uF 25V
C105 -> 100uF 450V, 120uF 450V or 150V 450V depending on monitor brand/model (bigger monitors use larger capacitors)
C102 -> usually unused, "X" capacitor for power filtering
C113 -> usually unused

[sermulis]

Re: Samsung Syncmaster 204B repair

Hi,

OK, i found and installed caps from spare boards.

C110, C111 - 1000uF 25VC
C112, C113 -> 470uF 25V
C304, C305 -> 470uF 25V
C105 -> 82uF 450V (bulked a little bit)

Found out that fuse F101 was dead (as i received it) - replaced the fuse.
Powered board on and received short -> Fuse F101 dead.

What do you suggest me to check ? What might be the cause for short in primary ?

[ant3202]

Re: Samsung Syncmaster 204B repair

perhaps check for any burnt components or transistor.

[budm]

Re: Samsung Syncmaster 204B repair

Probably shorted MOSFETs (there are two 8-pin SMD MOSFETs on the bottom side of the board), they drive the inverter transformers, check for low resistance reading between S and D. Get the P/N and the spec sheet for them, I would replace both of them.
http://s807.photobucket.com/user/bud...ml?sort=3&o=13

[sermulis]

Re: Samsung Syncmaster 204B repair

i've checked these both mosfets for shorts from source to drain and received no short circuits.. i should check resistance for these mosfets out of circuit?

[budm]

Re: Samsung Syncmaster 204B repair

Do you have the spec sheet of those two MOSFETs. If it is shorted (still on the board) when read with Ohm meter, then you can verify it again off the board. The fuse feeds the B+ to those two MOSFETs, so they must have been drawing too much current. BTW, what resistance reading are you getting on S-D.

[sermulis]

Re: Samsung Syncmaster 204B repair

unfortunately i was not able to read P/N from U202 and U203.
Board is 204B-VE REV0.1.

I guessed that pins 3&4 are for source and drain, because pins 5&6 and 7&8 are shorted (G1 and G2 pins)

On 3&4 I am receiving 24kOhm (in the circuit) on U202 and U203

I have replaced F101 one more time (had some spare ones). Removed inverter section to check if short is caused w/o inverter added by removing F301 fuse. Received short circuit one more time. So it seems short circuit is caused in Primary/secondary circuit. After short - i was able to read low voltage on C105 (5V), and no voltages at all on secondary circuit caps.

[budm]

Re: Samsung Syncmaster 204B repair

SP8K Dual N MOSFET.

[sermulis]

Re: Samsung Syncmaster 204B repair

S1toD1 and S2toD2 are not shorted for all. S2toD1 are shorted for all.
readings showed about 1,1MOhm when tested 1to8 pin.

You still think that it is mosfet failure although i powered the board without the fuse for the inverter section and it blowed fuse in primary circuit?

[sermulis]

Re: Samsung Syncmaster 204B repair

replacing diode bridge solved short circuit in primary.
now after power on i see blue diode light, but nothing on the screen and it's not possible to switch it on or off - just blue light

[budm]

Re: Samsung Syncmaster 204B repair

"i powered the board without the fuse for the inverter section and it blowed fuse in primary circuit" OK, you are confusing me, I thought you are blowing that PICO fuse, the one that supplying the voltage to the Inverter circuit section. If you are blowing the Main AC fuse, then you may have shorted bridge rectifier or the Power MOSFET that drives the main power transformer.
"it's not possible to switch it on or off" That will be the problem on the main/logic board.

[sermulis]

Re: Samsung Syncmaster 204B repair

what you suggest me to check now?

also, i've placed bulked 82uF 450V instead of 150uF 450V in primary, although i am getting 13V (which is OK) on CN2

[budm]

Re: Samsung Syncmaster 204B repair

Need to download the SCH for this monitor and start checking voltages on the main board.
So you are not blowing that small green fuse for the inverter?
http://elektrotanya.com/?q=showresul...oria=&kat2=all

[sermulis]

Re: Samsung Syncmaster 204B repair

no! sorry, if i confused you. power/inverted part seems to be ok now.

[budm]

Re: Samsung Syncmaster 204B repair

You may want to read this:
https://www.badcaps.net/forum/showth...04b#post246155

[sermulis]

Re: Samsung Syncmaster 204B repair

shorted 5&6 pins on EEPROM A81SC. (if arrow indicates first pin) didn't help.
also, it seems that i was too fast - saying that power/inverter part is working. i see no backlights (or logic board prevent them to start)

[budm]

Re: Samsung Syncmaster 204B repair

The logic board send out two signals to the inverter circuit, one is BL_ON (Backlights ON, or Inverter ON, ON = 2~5VDC), the other signal is Dimming signal for adjusting the BACKLIGHTS Brightness. So right now those two signals may not be there.

[sermulis]

Re: Samsung Syncmaster 204B repair

Right. Sending 0 volts for inverter on CN2