Dell E173FPb smoking

[maddog310]

Hi, great site you have here, i have been able to fix a few screens just by reading here. But don't know what to check next on this one, could be diode, resistor, or transformer not really sure.When i first fixed it, it had green power light then amber, black screen. I took it apart found one shorted c5707 (Q759) and one power mosfet J598 (Q751) and one blown 3amp pico fuse. Replaced with good used parts and new fuse, also desoldered transformers then resoldered them. Had it working for about four hours then it flickered a few times and back to black screen. Took it apart again, only a blown fuse. I put automotive bulb for fuse and tried it again, this is when the magic smoke happened. I then changed one blue cap (C757) don't think it needed to be changed, and resoldered one transformer (T753). Tried powering it up again backlights came on but the smoke also appearred, so i pulled the plug. I have attached pics, it looks like its shorted from c757 to t751, thats where the smoke was coming from. Maybe its getting to much power? You can see the burn mark in the partial pic. Sorry for the long spiel but wanted to say what i had did to this point. Thanx in advance for any help in this matter.

[Wizard]

Re: Dell E173FPb smoking

This one really suffers from bad quality component leads, transformer pins and bunch of very small electrolytic capacitors. Have to replace them and remove transformers, scrape pins clean, and reinstall, thoughly resolder components solder joints till they are wetted. Horrible.

Cheers, Wizard

[Mohonri]

Re: Dell E173FPb smoking

It sounds like the overcurrent protection isn't working. The schematic for the e173fpb's inverter is largely similar to the schematic for the e172fpb's. There's a PNP transistor (sorry, forget the number) for each backlight which shuts off if there's too much current, and sometimes, these fail to a short. IIRC they are FU9024N transistors. Replace these and see if it helps.

[maddog310]

Re: Dell E173FPb smoking

Thanks for the replies, I resoldered transformers, same issue, i did change one mosfet J598 43 with a J598 48 at (Q751) originally. My understanding is that the fet turns your backlights off. I'm wondering why its seems to be shorting if thats what it is doing, i have circled it in red, don't believe there is any trace there. Could it be a resistor, diode or transformer. Thanks for any replies.

[maddog310]

Re: Dell E173FPb smoking

Maybe this one is unrepairable, good for parts only. I would just like any opinions on why its burning in that particular spot, no trace there. I repaired a Benq monitor and works fine basically the same as this one. Don't believe power should go across there. Checked all 4 transistors, 2 fets, and fuses, still good after powering on and smoke making an appearance. Haven't changed any of the small caps as of yet, none on hand. Any thoughts! Tia.