Dell 2405FPW blown transformer?

[budm]

Re: Dell 2405FPW blown transformer?

Did you download the spec sheet of the IC? It will tell you where pin 1 is and the rest the of the pins of the IC.

[ucdzombie]

Re: Dell 2405FPW blown transformer?

Did you download the spec sheet of the IC? It will tell you where pin 1 is and the rest the of the pins of the IC.

I tried multiple sources. But the IC itself doesn't have any indentation or notch indicating the pin orientation. But by judging the orientation of the letters printed on the surface, I'm pretty sure I'm correct. Also I compared it with IC601, which has a couple of line indicating the orientation. Both IC have the exact same soldering style and pin number diagrams. So I'm assuming that's pin 8. In any case, IF this reading is what I got, does it indicate a bad IC?

[budm]

Re: Dell 2405FPW blown transformer?

Can you zoom in and take the pictures of the IC?

[ucdzombie]

Re: Dell 2405FPW blown transformer?

Can you zoom in and take the pictures of the IC?

[budm]

Re: Dell 2405FPW blown transformer?

See marked picture.

[ucdzombie]

Re: Dell 2405FPW blown transformer?

Can you zoom in and take the pictures of the IC?

See marked picture.

Thank you. And yes that's the exact same pin that I tested. The reading is 0.005v.

[budm]

Re: Dell 2405FPW blown transformer?

Thank you. And yes that's the exact same pin that I tested. The reading is 0.005v.

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.

[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?

[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.

[budm]

Re: Dell 2405FPW blown transformer?

BTW, these two fuses show <1 Ohms?

[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?

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.

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

[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.

[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?

'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?

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?

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?

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?

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).