Dell 2007wfpb inverter

[delaware74b]

I was 'gifted' with the above monitor, powers up but no display. On the inverter board (#5EL2J04011), I found one of the 2 transistors driving the center ccfl transformer had burned up.

My issue is the Rohm SP8M3 mosfets aren't available in the USA unless I go to China. I did find the Fairchild FDS8958B mosfet available from Mouser and Digikey. These mosfets appear to be better than the originals.

Question: Should I replace all 6 for a balanced drive of the ccfl section?

Obviously, I plan to recap the power supply and inverter to eliminate the Elite problem although none are bloated.

I'll post pictures of the inverter board tomorrow.

[delaware74b]

Re: Dell 2007wfpb inverter

I have uploaded pictures of the inverter board.

The third one shows the damaged mosfet.

Is there a good way to test the transformer (T802) either in circuit or out of circuit with just a DMM? I was looking at possibly getting the Anatek Ring Tester to test the transformer.

[PlainBill]

Re: Dell 2007wfpb inverter

I have uploaded pictures of the inverter board.

The third one shows the damaged mosfet.

Is there a good way to test the transformer (T802) either in circuit or out of circuit with just a DMM? I was looking at possibly getting the Anatek Ring Tester to test the transformer.

It's not a definative test, but about all you can do is measure the resistance of the secondaries. If either secondary on this transformer is more than 3% low, that is an indication it is shorted.

PlainBill

[retiredcaps]

Re: Dell 2007wfpb inverter

I have uploaded pictures of the inverter board.

Those are excellent pictures.

Is there a good way to test the transformer (T802) either in circuit or out of circuit with just a DMM?

This is NOT your transfomer, but it gives you an idea where the primary and secondary pins are.

http://www.lcdparts.net/TransformerD...ProductID=2726

The secondary pins should be within 3% of each other.

If it helps, I have this exact board in front me (waiting for repairs on the USB and logic board - shorted diodes and voltage regulators).

I get the following ohms readings on my Fluke 75

T801
S1-S2 = 1021
S3-S4 = 1016

T802
S1-S2 = 1028
S3-S4 = 1023

T803
S1-S2 = 1026
S3-S4 = 1021

edit: PlainBill beat me again while I was taking resistance measurements on my board.

[delaware74b]

Re: Dell 2007wfpb inverter

retiredcaps - thank you for your guidance. I definitely have something going on between the primary circuit and secondary for the center transformer. I am reading 15K between pins 1 - 2. Getting the same thing on 3-4, 5-6, 7-8. These pins are numbers on the board counterclockwise from the white dot.

The other two transformers were reading 10M minimum on the same pins. All secondary readings were pretty close, all between 1036 and 1043 ohms.

I am in the process of lifting the mosfets for t802 and going to take new readings

Photos were taken with cell phone (8.0MP Motorola Droid X) with macro turned on. I re-sized the photos to 1024x768 on my desktop before uploading.

[delaware74b]

Re: Dell 2007wfpb inverter

I got the mosfet lifted off the board and T802 transformer readings match the other 2 on the board.

I am looking at replacing the mosfet with the Fairchild FDS8958B. I am going to order enough to replace all 6 of the Rohm SP8M3's on this board and replacing the Elite Caps on the inverter and power supply boards.

[retiredcaps]

Re: Dell 2007wfpb inverter

Photos were taken with cell phone (8.0MP Motorola Droid X) with macro turned on.

Looks like the cell phone in another generation might actually be good enough to replace the low end consumer camera.

Most of the current phones still take photos that are too grainy.