Dell 2405FPW blown transformer?

[nomoresonys]

Re: Dell 2405FPW blown transformer?

Wondering if this was ever resolved?

[ucdzombie]

Re: Dell 2405FPW blown transformer?

Just a general reply and before I end this thread (since it's seemingly coming to a dead end and it's a waste of time for anyone to help). I understand that you all are doing great things by offering your expertise for free on this forum. I as a musician actually offer a lot of free work as well, such as composing free music for indy films, playing free concert for fundraising and hospitals. I understand how important it is for us to provide support for each other in a community. And I certainly encounter similarly frustrated situations like this where I try to help others, but the lack of proper communication or other reasons make it difficult for me to continue my free work. So I understand why you do/don't want to offer your helps. And it's no big deal. Thank you all anyway.

[ucdzombie]

Re: Dell 2405FPW blown transformer?

Budm, thank you for your help. But I just wanted to let you know that I'm not trying to complicate things here and I'm not an electrical engineer. I'm just trying to learn something and perhaps make the planet greener. So please don't get angry at me. I followed exactly what you said and tested the legs many times and there is no voltage. I can test it again. I did the resistant test just to see if the opto is ok. I don't see why this is wrong or bad. I'm merely curious and trying to provide more information and perhaps narrow the problem down. As far as the 1v difference between the two legs, it's true. I tested leg 1 in relation to the chassis ground, it's 7v, I tested leg 2 in relation to the chassis ground, it's 6v.

Again thank you and I will continue fixing it on my own.

[budm]

Re: Dell 2405FPW blown transformer?

"OK Just tested pin 1 and 2 (LED side) of the OPTO on a 10k ohm scale."
I do not know why you are testing the resistance when I ask you to check the DCV between the two legs of that OPTO.
As I said you need to check the DCV between the two legs of the LED which is inside the Opto and you report no DCV reading between the two pin so it is not getting the command on signal to turn on the OPTO.
BTW, are you 100% sure that there is no DCV between the two pins? What scale on the meter you are using? The Voltage should be a little less than 2VDC.

BTW, on post 38:

Just checked. The pin on the left has 35v, the other one has 30v.

That indicates 5VDC drop between the two legs, so that does not make sense either, when you now say you have 0V or 1V I am not sure any more.

There's no reading at all between the two pins when power is on. But there is continuity when power is off.

(BTW correction: one pin has 7v and the other has 6v. I was reading on the wrong scale).

"I'm still trying to make sense of the data sheet. But I just don't understand, if each leg has its own voltage, how can the two legs have voltage between them?"
Just look up how to light up LED. no Voltage on the LED then the LED will not light up, just think of it as a light bulb, no Voltage then the lamp will not light up, it is that simple.
Spec sheet of the OPTO?
You also need to get Digital meter tan do diode mode testing.
Did you also replace the blown fuse?
I gave up at this point, it is getting long and we are not getting anywhere, I will let someone else take over the troubleshooting.

[ucdzombie]

Re: Dell 2405FPW blown transformer?

OK Just tested pin 1 and 2 (LED side) of the OPTO on a 10k ohm scale. There's 0 ohm one way, and infinite ohm the other way (when I switched the probes). Doesn't this indicate the OPTO is bad because I'm supposed to have the same reading either way? I didn't de-solder it to run this test. Should I take it off and test it?

[ucdzombie]

Re: Dell 2405FPW blown transformer?

No DCV reading when measured right between the two pins that means the OPTO is not getting the signal to turn it on so there will be no DCV to tun the PFC IC.
You should look up the spec sheet of that OPTO to understand what it is and how it works.

Just got the data sheet and looking at it. Basically one side sends light signal and the other side receives it? I'm still trying to make sense of the data sheet. But I just don't understand, if each leg has its own voltage, how can the two legs have voltage between them?

[budm]

Re: Dell 2405FPW blown transformer?

No DCV reading when measured right between the two pins that means the OPTO is not getting the signal to turn it on so there will be no DCV to tun the PFC IC.
You should look up the spec sheet of that OPTO to understand what it is and how it works.

[ucdzombie]

Re: Dell 2405FPW blown transformer?

You need to measure between the two pins which represent the LED legs inside the OPTO.

There's no reading at all between the two pins when power is on. But there is continuity when power is off.

(BTW correction: one pin has 7v and the other has 6v. I was reading on the wrong scale).

[budm]

Re: Dell 2405FPW blown transformer?

Just checked. The pin on the left has 35v, the other one has 30v.

You need to measure between the two pins which represent the LED legs inside the OPTO.

[ucdzombie]

Re: Dell 2405FPW blown transformer?

So you need to find out if OPTO IC652 LED side is getting the Voltage between those pins of the IC or not when power switch is activated.
The output side of the OPTO is fed through R656? which is connected to the BASE of Q654.

Just checked. The pin on the left has 35v, the other one has 30v.

[budm]

Re: Dell 2405FPW blown transformer?

So you need to find out if OPTO IC652 LED side is getting the Voltage between those pins of the IC or not when power switch is activated.
The output side of the OPTO is fed through R656? which is connected to the BASE of Q654.

[ucdzombie]

Re: Dell 2405FPW blown transformer?

'EMITTER pin of the transistor Q654 has a voltage of 12v.' So there is DCV feeding the switched Transistor but the Transistor is not being turned on, you can verify it by checking to see if you have 0.6VDC between the E and B of the transistor or not.

'F702 is not important because it's a 7v line used for the speaker bar.' Are you sure? Dell Speaker bar runs on 12VDC, that is what I use. So to me you have shorts circuit that blow the fuse, if it is for speaker bar and you do not have speaker bar attached then why would it blow the fuse?

OK just checked. There's no reading at all between E and B. I also checked IC652, there's continuity between IC652 and IC651, but no continuity between IC652 and Q654.

Last night I replaced the smaller caps on the powerboard, and the output reading is now 18v, so 1v more than before.

I also noticed some relation between the blown F702 fuse and IC652. But I can't explain it. I have to mark another picture.

[budm]

Re: Dell 2405FPW blown transformer?

'EMITTER pin of the transistor Q654 has a voltage of 12v.' So there is DCV feeding the switched Transistor but the Transistor is not being turned on, you can verify it by checking to see if you have 0.6VDC between the E and B of the transistor or not.

'F702 is not important because it's a 7v line used for the speaker bar.' Are you sure? Dell Speaker bar runs on 12VDC, that is what I use. So to me you have shorts circuit that blow the fuse, if it is for speaker bar and you do not have speaker bar attached then why would it blow the fuse?

[ucdzombie]

Re: Dell 2405FPW blown transformer?

BTW, these two fuses show <1 Ohms?

Ok checked the fuses again. F701 is ok, full continuity. However F702 (newly installed last week) has very high ohm value and doesn't buzz when I test it for continuity. So it's blown. Although I was told and a couple of thread suggested that F702 is not important because it's a 7v line used for the speaker bar.

[ucdzombie]

Re: Dell 2405FPW blown transformer?

Can you take very clear straight shot pictures of the whole top and bottom side of the board? I need to make virtual PCB.

OK let's try these pictures. Let me know if you want me to hand draw the layout of the top board since some of the components cannot be seen clearly from certain angles. Also please use the photobucket links because this forum automatically re-size the pictures. Lastly, the EMITTER pin of the transistor Q654 has a voltage of 12v.

http://i196.photobucket.com/albums/a...ps8t8qejai.jpg

http://i196.photobucket.com/albums/a...ps5se0jknk.jpg

http://i196.photobucket.com/albums/a...psgjbxx5eb.jpg

http://i196.photobucket.com/albums/a...psnxxy8gpu.jpg

http://i196.photobucket.com/albums/a...psj30kg2u2.jpg

[budm]

Re: Dell 2405FPW blown transformer?

Collector of that transistor is the output pin to feed VCC to the IC, the EMITTER is the input pin which gets the VCC from ???
So what DCV do you have on the Emitter pin?
That Transistor is turned on by the Optoisolator IC652 which is turned on by the logic board.

[ucdzombie]

Re: Dell 2405FPW blown transformer?

Can you take very clear straight shot pictures of the whole top and bottom side of the board? I need to make virtual PCB.

Thank you so much budm. Yes I will take a very clear photo for you tonight.

I checked those two fuses in the picture before, F701 and F702. Although I didn't know the ohm value, the continuity test is OK and the voltage on both end are the same. So I assumed they're good. I can test the ohm value again tonight.

I'm able to do some tracing. And here's what I came up with (see picture). Basically pin 8 connects to the "C" pin of the transistor Q654 and has continuity. But there's no continuity between pin 8 and "E" pin of the transistor. On the other hand, I'm able to detect continuity between "E" pin and the top right corner of the PCB board, all the way to the medium size heat sink and the large yellow transformer is.

[budm]

Re: Dell 2405FPW blown transformer?

BTW, these two fuses show <1 Ohms?

[budm]

Re: Dell 2405FPW blown transformer?

Can you take very clear straight shot pictures of the whole top and bottom side of the board? I need to make virtual PCB.

[ucdzombie]

Re: Dell 2405FPW blown transformer?

You will have to trace that pin 8 to see where it goes next, it should be connected to Voltage source through some kind of switched Transistor, this is where the hard part comes in, tracing the board.

Yes it does connect to a transistor Q654, very close to the ic. I confirmed it with the continuity test. What should I look for in this transistor?