DELL 2405fpw

[Mirage00]

Re: DELL 2405fpw

I ordered this one today.

https://cdn.badcaps-static.com/pdfs/...4ea943619a.pdf

[budm]

Re: DELL 2405fpw

Great! you did not have it on long enough to kill the board, lucky you.
The main thing is that you have to be able to turn this 5V power supply on and off.

[Mirage00]

Re: DELL 2405fpw

Good News!! I disconnected the DC-DC converter I installed (since it was putting out 11v) for some reason and connected an old computer SMPS 5v line to the L1 connector to the T-CON board and TA-DA! The monitor worked perfectly After further research I realized I purchased a negative polarity version of the DC-DC converter board.

[Mirage00]

Re: DELL 2405fpw

I was afraid of that. Thanks for all your help though. It was an interesting experience.

[budm]

Re: DELL 2405fpw

That will damage the components and circuits on the T-CON, way too much voltage! It has to be 5V. That is one reason I suggested to use a resistor as a load so you can verify the voltage before hooking it up to the T-CON board.

[Mirage00]

Re: DELL 2405fpw

Update... it looks like the new power board is output 11v instead of 5v. Would over voltage to the t-con board cause white lines like that?

[Mirage00]

Re: DELL 2405fpw

OK here is my latest update. I replaced the 5v power circuit on the PCB according the link I posted above. The screen actually works now BUT I have white lines through the whole thing. I can see the computer screen through the white lines so somthing is working right. Not sure what to look at now. I attached pics of the modification and the monitor.

[budm]

Re: DELL 2405fpw

That may be the easiest thing to do. It will have to be at least 3A.

[Mirage00]

Re: DELL 2405fpw

Yeah. Ill add a separate 5v supply and see if that works.

[budm]

Re: DELL 2405fpw

That is too bad, the Gate voltage is not being switching on and off, so the buck converter IC and other components may be damaged.

[Mirage00]

Re: DELL 2405fpw

Ok no good Installed MOSFET and D19 DIODE and left the T-CON disconnected... Took a voltage reading of the DRAIN and it was 0 again. Both gate and source where 18.8 where they were last time. So I guess the gate logic is bad?

[budm]

Re: DELL 2405fpw

OK, it may not be shorted but it does not mean it is OK, it will have to be tested with active tester. I would replace it any way.

[Mirage00]

Re: DELL 2405fpw

Ok I removed the MOSFET and tested OHMS between drain and source... it stayed on 1. So I guess its not shorted?

[budm]

Re: DELL 2405fpw

Please see the picture.

[Mirage00]

Re: DELL 2405fpw

Ok I think I follow. Keeping in mind that I am not an expert, where would I connect the resistor ? Do I connect one end to the dran and the other end to what?????

[budm]

Re: DELL 2405fpw

If I read his post correctly, that Zener Diode is for protecting the Gate of the MOSFET, not for protecing the whole 5V circuit., If that 5V is for feeding the T-CON only and NOTHING else, then you can find out if the it is putting out 5V or not by not connecting the cable to the T-CON, but install 100 Ohms 1/2Watts resistor as a load instead.
IF the IC that drives the MOSFET is bad and causes the MOSFET to be stuck on instead of swithing, then the output voltage will be the same as the input voltage, which is around 20V (it basically not stepping down the voltage as it should).
I forget, does the MOSFET has shorts between Source and Drain? You may want check when you remove the MOSFET.

[Mirage00]

Re: DELL 2405fpw

Ok everyone I have one last question before I proceed since the parts (Zener diode for D19 and 5305S MOSFET) arrived today. In speaking with the person who repaired his 2405fpw by adding its own SMPS to supply 5volts to the T-CON board, he said if I replace the MOSFET and diode, chances are it will blow again and could cause more extensive damage to the unit. He reccomended just replacing the 5v supply as he did. What do you guys think? Doesnt the diode (d19) prevent downstream circuits and gate logic from damage?

Thanks

[Mirage00]

Re: DELL 2405fpw

Got it.. thats why he said "without further help from DELL (schematics)" he had to replace the regulator. Thanks again budm

[budm]

Re: DELL 2405fpw

There is an IC that drive the Gate of the MOSFET (at 40~80KHz a second) , when you have Drain to Gate shorted, it will usually take out the protection Diode and sometime the output circuits inside the IC also, I hope it is not in your case. At this point I am not sure which IC that is for this buck regulator.

[Mirage00]

Re: DELL 2405fpw

One more question.. in the other thread he said "I am not sure I want to replace the FET, for fear that the gate controller logic may be fried"

I would imagine the zener is their to protect the circuit in case the FET blows. What did he mean by gate controler logic. Isn't that within the FET?