Dell E153FPb failed transistor replacement

[CalvinSays]

Hello, this is my first post to this forum

Having read about replacing the transistors Q743, Q739, Q740 and Q751, Q759, Q760 and resoldering the coils T752 and T751; I have possibly done something wrong because... Q743 gets immediately very hot to touch and I think the fuse would go if I didn't turn the power off.

The Q751, 759, 760 part of the circuit appears fine because when I remove Q743 all is well and the power LED lights up fine. The screen lights up and then goes off.

I have two of these monitors and have replaced T752 with no effect. I'm using direct replacements bought from a kit on ebay.

Can anyone give me some pointers as to what to try next? I'm not an electronics expert (as you can probably guess otherwise I wouldn't be posting this )

Any help appreciated.

[Bobdee]

Re: Dell E153FPb failed transistor replacement

You may have made the same mistake that I made with this board
When replacing the transistors, I put one in the fet position thinking it was the fourth transistor position
One of the transistors is in a unusually offset position on this board
Hope this helps
Or possibly one has been put in backwards, an easy mistake to make

[CalvinSays]

Re: Dell E153FPb failed transistor replacement

Hello Bobdee,

Thanks for your reply which was just the tonic. I looked again and would you believe I had soldered in Q739 in the wrong way in both monitors! In one monitor just swapping it around fixed it but in the other I to replace Q740 which either was already faulty or had not survived my idiocy.

On the Q759, Q760 pair they are metal side facing metal side and I just copied that with Q739, Q740 but on closer inspection the board is labeled Q759 ECB, Q760 BCE whereas the other two are BCE BCE. I think from now on I photgraph the board and check is all looks ok before switching on.

Both monitors are working fine at the moment though I wonder if the FETs will last long. Won't make that mistake again (probably will).

Thanks again

[Bobdee]

Re: Dell E153FPb failed transistor replacement

Nice to hear some good came out of it
One little reminder on these Benq boards, I take it that you have resoldered the 4 inverter transformers, as this is believed by many to be the cause of the failure of the transistors, (if not done transistors usually fail again) also check the rest of the board for bad solder joints as its usual to have some bad solder joints elsewhere

[CalvinSays]

Re: Dell E153FPb failed transistor replacement

Yes I did resolder the transformers. There are some good articles on the net and they recomended doing it. The monitors are in use and still working fine