Samsung 940n wont turn on

[CroTech]

Re: Samsung 940n wont turn on

The power board supplies 4,8V on third pin (pin3: 4,5V) the connector that connects logic board and power board...

Also I can measure 5,3V on the logic board as u can see in the picture

[selldoor]

Re: Samsung 940n wont turn on

Hi - Happy new year- you must think I am bonkers I have just looked at the link in post 7 and of course it does not relate at all - You should have told me!

This is what you should have had

https://www.badcaps.net/forum/showthread.php?p=261329

Yes based on the voltages you have on the VRs on the board they are
faulty BUT they can be tested agian off the board with a battery. I will try and find how to do it - it may even be in the guide.

[CroTech]

Re: Samsung 940n wont turn on

Sorry for "ignoring" that post

I actually googled: retiredcaps how to test a voltage regulator

So I did it that way... If u can make/show me the guide on how to test those, I am willing to desolder them and try it out

[selldoor]

Re: Samsung 940n wont turn on

Cant find it but its basic stuff for the 1.8v one you use 2 x1.5 batteries
in series and use that as v in and test v out. Connect across gnd ( pin 1 )
and Vin (pin 3 ) and test on Gnd and vout (pin2 and/or the tab)

For the 3.3 use 3 x1.5v batteries.

[Rtech]

Re: Samsung 940n wont turn on

Test the supposed 3.3v output one first...as explained the 1,8v one may not be faulty.

[CroTech]

Re: Samsung 940n wont turn on

Desolder first and then do the test or I can do it even when they are on the board?

So two in series will give me steady 3V, I put minus (GND) on pin1 and + (3.0V) on pin 3 and then read pin2?

[Rtech]

Re: Samsung 940n wont turn on

That is correct.Although I would take off the board the one that is supposed to give you 3.3v output and measure the voltage between the pads on the board for pins 1 & 3,and ensure that the input voltage is there to allow the regulator to work.

[CroTech]

Re: Samsung 940n wont turn on

Thanks Rtech, I will desolder the one that gives 3,3V...
Just askin, whats the voltage this one needs? I have a lot of power adapters, so it is easier for me to take one than connecting three batteries...

[Rtech]

Re: Samsung 940n wont turn on

Ideally you would have to check the datasheet,But i would think anything up to 9v should be ok.
But check across the pads first,to ensure you have the input voltage for the regulator.

[selldoor]

Re: Samsung 940n wont turn on

You would nee d to be careful using and adapter- If it is not regulated and you use 9 volts it could actually produce 11 or 12v or possibly more when it does not have a load. If you really must then use a 5v phone charger

[CroTech]

Re: Samsung 940n wont turn on

I used a 5V adapter that turned out to give 7,68V

So, the 3,3V voltage regulator gave these readings:
pin1 0V
pin2 3,29V
pin3 7,68V

I assume it´s good so, I am going to desolder 1,8V and check it

[Rtech]

Re: Samsung 940n wont turn on

Thats good.DID you check the pads on the board as suggested ??????/before you put it back on.
IF there is no input voltage on them, then you will obviously not get the output 3.3v.

[CroTech]

Re: Samsung 940n wont turn on

The 1,8V gives
pin1 0V
pin2 1,8V
pin 3 7,68V

What now?

And just to experiment, i put black probe on housing solder and than on pin1 it gave -1,8V so that means the housing is connected to the second pin and thats ok? That means the housing is output and pin3 is input?

[CroTech]

Re: Samsung 940n wont turn on

Pads n the board as sugegested? I dont understand that? U mean to solder it back with the adapter and than measure or?

[CroTech]

Re: Samsung 940n wont turn on

something is gotta be wrong with the power board since the voltage regulators are only getting 0,7V for 18 and 1,6V forr 33...

my only idea is to change the capacitor on the picture, and it´s not even a crapxon :/

[Rtech]

Re: Samsung 940n wont turn on

Not necessarily the case !! I meant that when you had 3.3v output regulator OFF the board, you then measure the voltage on the pads on the board where the regulator would normally fit.So that will show if you are getting the input voltage going to the input pin that is pin 3 !!!.You also when you have done this,AND there is NOT the approx 5v input,then you need to measure where that input voltage comes in to the board on the connector from the Power supply Board,and measure there with the logic Board connected,and then just on the Power supply board,when you take the logic board away.So then you will know if the fault is on the Logic or Power Supply Board.

[CroTech]

Re: Samsung 940n wont turn on

So buying a new power board wouldn´t be a clever thing to do since the problem still could be in the logic board?

[Rtech]

Re: Samsung 940n wont turn on

Correct.The problem can be either that the Logic board has a fault which is pulling the 5v input from the Power Supply board down,or the power supply cannot give enough CURRENT out to maintain its 5v output if any load(ie the Logic Board) is placed on it(sometimes that can be caused by a bad cap).To try and pinpoint the problem,then you need to do as I suggested by measuring the 5V output from the Power supply board, when the logic board is connected,and when it is then taken away.

[selldoor]

Re: Samsung 940n wont turn on

I think he already measured 5 volts on the main board with the boards connected. Post21
Can you test the two diodes D600 and D603

Try for the voltage again then see where else it appeard test the voltage on each end of each Diode.

[Rtech]

Re: Samsung 940n wont turn on

I think he already measured 5 volts on the main board with the boards connected. Post21
Can you test the two diodes D600 and D603

Try for the voltage again then see where else it appeard test the voltage on each end of each Diode.

Thers may be some confusion has crept in !! On the Power supply photo he shows 7 Pins with the 5v on pin ONE.On the logic board it actually shows 9 pins, and the 5.3 volts measured were on pin Two,they do not look as they are shorted together,but maybe ???.I am a big fan of those diodes going faulty and it is as well to check,but it may well be the Cap that filters the 5v that is causing the problem,and needs to be changed as the first immediate action.