Samsung Syncmaster 245BW

[tibimakai]

Re: Samsung Syncmaster 245BW

I have just replaced the IC and the monitor is alive!!
Thank you all again for your help. Now I have to go back to that Asus with the burned resistors.

[budm]

Re: Samsung Syncmaster 245BW

http://s807.photobucket.com/albums/y...t=DSC01679.jpg

http://s807.photobucket.com/albums/y...t=DSC01681.jpg
Yes, just the lamp in series with the line side of the outlet.

[budm]

Re: Samsung Syncmaster 245BW

Well that is great news that you have found the shorts, you will get better and better as you begin to understand how the circuits work, just take time, I am still learning and trying to understand how things work everyday.

[tibimakai]

Re: Samsung Syncmaster 245BW

I have just removed the IC and I don't have 3.3 ohms there.
So I'm ordering a new IC.
Thank you very much for your help, without you I wouldn't be able to repair these monitors and TVs.
I still have a couple which needs your or others help.
I have just checked the Asus monitor(burned resistors) and the TA1530A is not getting enough Vcc, only 1.79V.
I still have an LG TV with a short somewhere and a Philips TV that it's dead.
If everything goes well, tomorrow I'm getting my first LED TV, it's a Vizio M420NV. I'm anxious to see how it's inside.
Sorry to be so off topic, but since you are following this repair of this monitor you will read most likely much faster this message.
Could you please send me the diagram or pictures of that short circuit test stand that you have made? I have purchased the components for it, I just need to put them together. Everything is in series?

[budm]

Re: Samsung Syncmaster 245BW

OK, now the output voltages are close to what I have expected from these two regulator transistors.
Now you just have to find out why you have 3.3 Ohms on that pin 8 of the IC.
You are getting close to the cause of the problem.

[tibimakai]

Re: Samsung Syncmaster 245BW

Ooops, I have installed 803 backwards.
now I have:
803
C=28V
B=20.69V
E=20.66V

I will have to remove both capacitors, but a bit later today.

[tibimakai]

Re: Samsung Syncmaster 245BW

You are right, I will double check my measurements.

[budm]

Re: Samsung Syncmaster 245BW

"QB803
C=10-16.5V oscillating
B=11.3-17.3V oscillating
E=10.5-16.6V oscillating
B802
C=28V slight oscillation
B=16.02V
E=16.06V
ICP801S's pin #8 and GND= 3.3 Ohm"

OK, something is wrong here since Collector of Q802 and Q803 are tied together and connected to 68 Ohm output side, so please check that again, they should have exact same voltage reading.
Pin 8 ICP801S reading short circuits, so remove the filter caps on that pin 8 and see if the shorts goes away, otherwise, you have shorted IC.

[tibimakai]

Re: Samsung Syncmaster 245BW

Finally I had some time to do these measurements.
What I did:
removed both transistors and re soldered them on the back of the board with the emitters in the air.
QB803
C=10-16.5V oscillating
B=11.3-17.3V oscillating
E=10.5-16.6V oscillating
B802
C=28V slight oscillation
B=16.02V
E=16.06V
ICP801S's pin #8 and GND= 3.3 Ohm
Main cap voltage is oscillating 157-161V

[budm]

Re: Samsung Syncmaster 245BW

Q802, Q803 circuits without the loads connected to their Emitter will not cause the load down of the supply voltage.

[tibimakai]

Re: Samsung Syncmaster 245BW

I haven't tested the Q802 this way, I have just removed it completely.
It's late now, I will do these measurments tomorrow.
I have a feeling that something between the two transistors will be the culprit.

[budm]

Re: Samsung Syncmaster 245BW

What voltage do you get at the base of the Q803, especially the voltage on that Zener Diode.
What do you get at Emitter of Q802 Collector, Base?

[tibimakai]

Re: Samsung Syncmaster 245BW

sorry, I forgot to add that 1.2V is at the emitter, with the emitter lifted(QB803).

[budm]

Re: Samsung Syncmaster 245BW

That cannot be since you have indicated that one of the cap for the 24v power supply filter cap has blown up, 1.2V will not be enough for the 24v power supply to run. What do you get at the Emitter of Q803 when choke BB803 is lifted. when both Emitter legs of Q802, Q803, there will hardly be any load on the output side of the 68 Ohms. Please recheck your measurement.
I need to know what voltage you are getting at the Emitter of both transistors without the load connected.
By the what ground point are you using for this Primary AC circuits?

[tibimakai]

Re: Samsung Syncmaster 245BW

On the emitter of the QB803 I have 1.2V.
3x68 ohm no change.

[budm]

Re: Samsung Syncmaster 245BW

The 68 Ohms resistors feed two voltage regulator transistors. The resistors are getting hot because too much current is flowing, we need to start removing the loads, so it looks like the Q802 is feeding very low resistance load. You should Check the resistance of the IC ICP801S Pin 8 (vcc) and Ground with Emitter of Q802 still not connected.
CM863 is in parallel with other two 24V filter cap, lifting that Emitter will not kill the cap, otherwise the other two would have blown up aslo. Right now the 24Vdc power supply is working now (should verify that it is putting out 24V, but it may not be since the PFC is not on due to Q802 is not connected) since Q802 and its load is no longer loding down thw output of the 68 Ohms resistors.
You need to check the output voltage if the transistor regulator out as I have shown.

[tibimakai]

Re: Samsung Syncmaster 245BW

Here they are.
The IC 801S I have changed and I didn't do a "nice job", some of the pads have lifted off, but they make contact.
Since these pictures I have replaced that capacitor(470uf/35V) and reinstalled QB802 and everything is back on how it was.
I have measured again the CP805 and it measures 3.3ohm(with or without it).

[tibimakai]

Re: Samsung Syncmaster 245BW

T, I will take those shots in a few.

[tibimakai]

Re: Samsung Syncmaster 245BW

The only difference made, when I removed the QB802 transistor.
The voltage at the 3x68ohm output raised to 24.99V, but I forgot to check the input voltage at the 3x68ohm resistors. Unfortunately one of the caps blew up("hissed" leaked acid) CM863.
I guess, I shouldn't live the power on for so long with a transistor removed.
We are getting somewhere, that's good.
I have checked transistor QB802, and checks out OK.
I haven't seen anything strange about CP805 or CM811.
Lifting BB803 didn't make any difference.

[Toasty]

Re: Samsung Syncmaster 245BW

CLEAR & BIG Photos of the back of your board please.

Back of board, AC power connection to the right, lower-left 1/4 of board from the transformer to the edge with the 2 connectors.

T