Samsung Syncmaster 245B

[Rhodri2311]

Re: Samsung Syncmaster 245B

Ok slightly hungover following the Welsh rugby loss but should be fine to tinker today Is there anything else I can check or you can suggest I try? Cheers!

[retiredcaps]

Re: Samsung Syncmaster 245B

The voltage readings on the logic board look good.

On the power board, you are not getting 24V or 5V.

What is the DC voltage across the main filter capacitor? Hint: This is very high voltage and measuring it when hungover may not be a good idea.

It should be 220V AC x 1.414 or roughly 311V DC. So put your multimeter on something higher than 400V DC.

[retiredcaps]

Re: Samsung Syncmaster 245B

I forgot to mention that on the logic board there should be a label for on/off. It should be written on the connector somewhere. Or it could be labeled on the power board?

This voltage will be 0V DC when off and probably > 3V DC when on. So when you press the on/off button, this pin should change in voltage from 0 to 3V DC.

[Rhodri2311]

Re: Samsung Syncmaster 245B

There's a pin on the logic board called power_en could that be it?

[Th3_uN1Qu3]

Re: Samsung Syncmaster 245B

Yup that's it.

[Rhodri2311]

Re: Samsung Syncmaster 245B

Ok the main cap puts out around 320v and on/off goes to 3.3v with the lcd on.

[retiredcaps]

Re: Samsung Syncmaster 245B

Ok the main cap puts out around 320v and on/off goes to 3.3v with the lcd on.

Okay, please verify if the voltage 24V and 5V DC on the power board is present or missing.

[Rhodri2311]

Re: Samsung Syncmaster 245B

There's no output 24v DC at all I can see, and the 5v seems to be around 0.05 (although this one did seem to fluxtuate every now and again).

[retiredcaps]

Re: Samsung Syncmaster 245B

There's no output 24v DC at all I can see, and the 5v seems to be around 0.05 (although this one did seem to fluxtuate every now and again).

Okay, this implies that the SMPS power supply is not starting for some reason.

1) It could be a bad small capacitor either dried out or has high ESR.

2) It could be the SMPS controller chip is bad.

Service manual is here



PS. We will also need a clear focused photo of the backside of the power board.

[Rhodri2311]

Re: Samsung Syncmaster 245B

Thanks for that, downloaded the manual, not really sure what I'm looking at though. Here's the pictures of the underside of the power board.

[retiredcaps]

Re: Samsung Syncmaster 245B

Okay, this thread has a ton of info.

https://www.badcaps.net/forum/showth...highlight=245B

1) If you haven't seen it, try measuring RB805, RB806, and RB807. One may be burned?

2) Check QM802 to see if it is open.

3) Check fuse FB802S.

Anyone of the above could be the cause of the SMPS not starting. Details of all 3 are in the above thread.

[Rhodri2311]

Re: Samsung Syncmaster 245B

Do you mean to measure the voltages? RB805, 806 & 807 all appear to be scourched quite a lot.

Fuse seems to be ok, resistence measures 0.04

How do I test QM802? I can see it marked on the bottom of the board but not tell what part it's connected to as there are lots next to it.

[retiredcaps]

Re: Samsung Syncmaster 245B

Do you mean to measure the voltages? RB805, 806 & 807 all appear to be scourched quite a lot.


How do I test QM802?

Set your multimeter for 200 ohms for the resistors. You can test them "in circuit". Report measurements for all resistors.

For QM802, if it is a 3 legged IC, measure the resistance between 1-2, 1-3, and 2-3. Report all measurements.

[retiredcaps]

Re: Samsung Syncmaster 245B

How do I test QM802? I can see it marked on the bottom of the board but not tell what part it's connected to as there are lots next to it.

Where is QM802 on your board? I can't seem to find it. I see a QB802 near the resistors. I got the QM802 designation from the other thread.

If QB802 is the "correct" part for your board, also check QB801 and QB803.

[Rhodri2311]

Re: Samsung Syncmaster 245B

RB806 & 807 measured close to 67 each, 805 there was no reading at all so looks like that may well be dead.

QM802 I'm still confused by - this is what I'm looking at.

[retiredcaps]

Re: Samsung Syncmaster 245B

RB806 & 807 measured close to 67 each, 805 there was no reading at all so looks like that may well be dead.

QM802 I'm still confused by - this is what I'm looking at.

Remove RB805 and retest out of circuit.

I still can't see what you are looking at for QM802. Maybe circle it so I know what you are looking at.

Test QB801, QB802, and QB803 for sure though using the method I described above with 1-2, 1-3, and 2-3.

[Rhodri2311]

Re: Samsung Syncmaster 245B

Sorry it's not very clear in that photo - QM802 is marked above RM812, I'm not sure what part to test though. When you say 1-2 for example do you mean the pins on it?

[retiredcaps]

Re: Samsung Syncmaster 245B

Sorry it's not very clear in that photo - QM802 is marked above RM812, I'm not sure what part to test though. When you say 1-2 for example do you mean the pins on it?

Normally transistors are 3 pins. Some are more. For a 3 pin transistor, just number them 1, 2, 3. Measure the resistance between pin 1-2, 1-3, and 2-3.

[Rhodri2311]

Re: Samsung Syncmaster 245B

Taken RB805 out and it's dead. Tested qb801 02 and 03 but couldn't get a result on any of them.

[retiredcaps]

Re: Samsung Syncmaster 245B

Taken RB805 out and it's dead. Tested qb801 02 and 03 but couldn't get a result on any of them.

If QB801, QB802, and QB803 all read out of range, 0L, or "1", then they are good.

So order a new resistor and retest.