Samsung Syncmaster 245BW

[budm]

Re: Samsung Syncmaster 245BW

"the ICP801S (PFC IC) Vcc is 1V only which should above 15V. And the Vcc on IC801S (SMPS IC) is 14V" That does not make sense, QB801 linear regulator circuit (TO-220) Emitter is the output pin that has the output voltage directly to feed the PFC IC ICP801S (smd), and the 24V SMPS IC ICM801 (MC33067) VCC pins.

[sky007]

Re: Samsung Syncmaster 245BW

"the ICP801S (PFC IC) Vcc is 1V only which should above 15V. And the Vcc on IC801S (SMPS IC) is 14V" That does not make sense, QB801 linear regulator circuit (TO-220) Emitter is the output pin that has the output voltage directly to feed the PFC IC ICP801S (smd), and the 24V SMPS IC ICM801 (MC33067) VCC pins.

Sorry, my mistake. You are right, SMPS IC ICM801 Vcc is same as ICP801S (PFC IC) Vcc, 1V only. I got 14V on ICB801S Vcc pin.

[budm]

Re: Samsung Syncmaster 245BW

Then you need to check the Voltage on the Collector (metal tab) of QB801 that is the input pin, you are check voltage on the primary side so you have to use the negative leg of the main filter cap as the ground ref point. If you do have 15~20V on the Collector, then you need to find out if the Base - Emitter does show 0.6~0.7VDC, you have to make sure to supply PS_ON to the board to turn on this transistor.

[sky007]

Re: Samsung Syncmaster 245BW

Then you need to check the Voltage on the Collector (metal tab) of QB801 that is the input pin, you are check voltage on the primary side so you have to use the negative leg of the main filter cap as the ground ref point. If you do have 15~20V on the Collector, then you need to find out if the Base - Emitter does show 0.6~0.7VDC, you have to make sure to supply PS_ON to the board to turn on this transistor.

On the Collector, read 0.7 - 1.4V, Emitter 0.6-0.9V.

[budm]

Re: Samsung Syncmaster 245BW

The Collector is not getting the rectified voltage from the aux winding of the StBY transformer.
The output pin of the AUX winding is fed to resistor RB804, then the Rectifier diode DB80, the Cathode of DB804 is connected to the Collector of the transistor. We know the STBY circuit is working so you need to trace that out and see why you are not getting the DC at the Collector.
Cap CB809 (47uF 50V) is the filter cap for filtering the DC.

[sky007]

Re: Samsung Syncmaster 245BW

The Collector is not getting the rectified voltage from the aux winding of the StBY transformer.
The output pin of the AUX winding is fed to resistor RB804, then the Rectifier diode DB80, the Cathode of DB804 is connected to the Collector of the transistor. We know the STBY circuit is working so you need to trace that out and see why you are not getting the DC at the Collector.
Cap CB809 (47uF 50V) is the filter cap for filtering the DC.

If I take out QB801, am I able to get aux output voltage on Cb809?

[budm]

Re: Samsung Syncmaster 245BW

Yes, that voltage should be there as long as the standby voltage circuit is working, so when you apply AC to the board, the voltage should be there right away, if not, check the resistor to see if it is open, it is <10 Ohms resistor for protection.

[sky007]

Re: Samsung Syncmaster 245BW

Yes, that voltage should be there as long as the standby voltage circuit is working, so when you apply AC to the board, the voltage should be there right away, if not, check the resistor to see if it is open, it is <10 Ohms resistor for protection.

I will do tomorrow and let you know. Thanks.

[sky007]

Re: Samsung Syncmaster 245BW

I think QB801 is bad. I take it out from board, and get reading from base 15.61V, Collector 17.56V, Emitter 0V.
But strange thing is, test QB801 off board, switch multimeter to diode test, read B-E 577, B-C 577, E-B 1, C-B 1, E-C and C-E both get 1. It looks good.

Can't find exact mode on ebay, but I find TIP41C 6A 100V NPN Transistor. Is it good as replacement?

[budm]

Re: Samsung Syncmaster 245BW

To turn that transistor it should have Base to Emitter voltage of at least 0.6VDC.

[budm]

Re: Samsung Syncmaster 245BW

Are you supplying 3VDC to the PS_ON PIN?
The setup is really close to *-192 board (the designators are not the same but the connections are very similar). V ery similar to QB802 on page 1.

[sky007]

Re: Samsung Syncmaster 245BW

Yes, I have that document. It help me understand how it work. I find some different, but mostly part are same.

Yes, using a 330k resistor connect Sb and PW_On, so I do have PSON 3V signal.

With QB801 on board, Base 0.55-0.88v, Collector 0.7 - 1.4V, Emitter 0.6-0.9V.

Without QB801, base 15.61V, Collector 17.56V, Emitter 0V.

But test QB801 individually by multimeter, switch multimeter to diode test, read B-E 577, B-C 577, E-B 1, C-B 1, E-C and C-E both get 1. It looks good.

Anyway, I will change it first.

[budm]

Re: Samsung Syncmaster 245BW

"330k" that is way too high, it should be around 100~1K Ohms. @330K, there will not be enough to turn on the PS_ON transistor.

[sky007]

Re: Samsung Syncmaster 245BW

"330k" that is way too high, it should be around 100~1K Ohms. @330K, there will not be enough to turn on the PS_ON transistor.

Sorry, it is 3.3k Ohms. I indeed have 3v on PS_ON. The PC802S is On, otherwise I should not have voltage reading on one end of RB815 which connect to QB801 base.

I just do not understand why the transistor off board testing is good, but on board shows bad. Is any other component failure could cause trouble?

[budm]

Re: Samsung Syncmaster 245BW

If you check the resistance between the primary ground and the Emitter, what do you get?
You can also force that transistor on by shorting the Photo transistor E and C together.
There is not much in that regulator circuit.

[sky007]

Re: Samsung Syncmaster 245BW

If you check the resistance between the primary ground and the Emitter, what do you get?
You can also force that transistor on by shorting the Photo transistor E and C together.
There is not much in that regulator circuit.

Between the primary ground and the Emitter only 24.7Ohm.

Shorting transistor E and C, so the PW_ON would not need, and transistor E will be fed by AUX directly (17.56V), am I right?

[sky007]

Re: Samsung Syncmaster 245BW

Shorting transistor E and C, voltage on E show 0.18V, main Cap still only get 170V.
Something wrong.
Maybe we can say the transistor QB801 is good. The loads of M_Vcc get problem.

[sky007]

Re: Samsung Syncmaster 245BW

I get little progress. I put back QB801, and open JB805 which feed M_vcc to IC801S (SMPS IC), break the connect J808 which feed M_Vcc to ICM801, then between the primary ground and the QB801 Emitter read 7.2k Ohm, the voltage on Emitter is 17.56V now.

If one of jumpers connect, I would not get 17.56V on QB801.

Is it possible the IC801S and ICM801 both blow out?

[budm]

Re: Samsung Syncmaster 245BW

That is why I request to to check the resistance on the Emitter and primary ground to see if there is shorted circuit or not since the Emitter is connected to the VCC pin of the PFC IC and the 24V SMPS IC.

[Gerry]

Re: Samsung Syncmaster 245BW

Attached are pictures of the tabs on the bezel you will need to pry and pass
them by to remove the cover. There are 6 of these tabs on the top and
bottom ends and 4 on each side of the monitor. I have a home made bamboo
tool I use to go around the periphery of the cover and bezel to snap each of
these tabs away from the cover one by one. Once all of them are off the
cover you should be able to remove the cover easily. You can use two flat
blade screwdrivers in a pinch to remove the cover. I usually start the opening
of the cover somewhere near the middle top or bottom side. Use one
screwdriver to hold the initial position and a second one to go around the
periphery of the monitor. Good luck.

This was a great help - thanks!