two Dell 172FPb both have TWO SECONDS TO BLACK

[Mad al]

I have two Dell 172FPb both have TWO SECONDS TO BLACK.
Board 1 the power light stays on.
Board 2 the power light flashes.

I jump stat to checking the C5707 Transistors to see if any are Shorted.
Haveing the Digital Multimeter on 200 and doing a reading from the solder side
The transistors C5707 pins are mark on the board as B,C,E,


Board 1:TWO SECONDS TO BLACK the power light stays on,
transistor Q760:B+C= 01.8, B+E=130.8, C+E=129.5:
transistor Q759:B+C= 02.1, B+E=130.7, C+E=128.7:
transistor Q740:B+C=1 . , B+E=1 . , C+E=137.8:
transistor Q739:B+C=1 . , B+E=1 . , C+E=137.7:
transistors Q740 & Q739 are Shorted need to be replace ?

Board 2:TWO SECONDS TO BLACK the power light flashes,
transistor Q760:B+C=1 . , B+E=1 . , C+E=130.9:
transistor Q759:B+C=1 . , B+E=1 . , C+E=130.8:
transistor Q748:B+C= 01.2, B+E= 15.7, C+E= 15.7:
transistor Q739:B+C= 01.0, B+E= 15.6, C+E= 15.4:
transistors Q760 & Q759 are Shorted need to be replace ?
was hopping to use Q740 & Q739 in board 1,
But low ohm on transistors Q740 & Q739 thay may be Shorted too ?

Can I replace transistors C5707 with C5706 ?
Let me know if i am way off the mark just a newbe here.

[retiredcaps]

Re: two Dell 172FPb both have TWO SECONDS TO BLACK

Haveing the Digital Multimeter on 200

1) 200 what? 200 ohms? 200V AC? 200V DC?

2) If Ohms, then Q760 and Q759 are shorted on board 1. Q748 and Q739 are shorted on board 2.

3) Use proper replacements. C5707s are widely availabe on ebay (I know since I purchased them off ebay). You can get 10 of them for less than $5 + free shipping. Replace ALL your c5707s as they work in pairs and may be subject to fatigue.

4) Since there is no picture, I can only guess these are the infamous Benq boards that have the bad soldering on the inverter transformers. Resolder ALL your inverter transformer pins. It is mandatory.

5) Looks like budm was posting at the same time I was. So I won't repeat his advice as well.

[budm]

Re: two Dell 172FPb both have TWO SECONDS TO BLACK

They are bad, if I can assume that he knows how to use the meter properly.
2SC5706 has lower rating than the 5707, I would not use the 5706.
Also check the fuse PF751, should be around 1 Ohm. Also resolder connection on the transformers, component legs, inspect them real well with magnifying glass.
Check the caps by the transistor, and the transistor Q743 (there are two of this transistor) that supply the power to 2SC5707.
There are more than one version of this model, you can see more pictures here:
http://s807.photobucket.com/albums/yy352/budm/DELL/

[Mad al]

Re: two Dell 172FPb both have TWO SECONDS TO BLACK

retiredcaps yes sorry I was useing 200 ohms.
Yes it be the infamous Benq boards,
Same as the Attached Thumbnails budm just posted.
budm the fuse PF751 are 0.6 ohm reading at 200 ohm on both boards.
The transistor Q743 & Q751 are reading :B+C=1 . , B+E=1 . , C+E=1 . : on both boards, So there ok.
Reading the caps at 200 ohm is showing no shorts, If thats right ?

[retiredcaps]

Re: two Dell 172FPb both have TWO SECONDS TO BLACK

r
The transistor Q743 & Q751 are reading :B+C=1 . , B+E=1 . , C+E=1 . : on both boards, So there ok.
Reading the caps at 200 ohm is showing no shorts, If thats right ?

Correct. Q743 and A751 are not shorted because the resistance reading is greater than 200 ohms. At this point, we don't care what the actual resistance is.

[Mad al]

Re: two Dell 172FPb both have TWO SECONDS TO BLACK

What size picofuse are on these boards? like to make a oder for them but don`t know witch one`s Iam looking for.

[retiredcaps]

Re: two Dell 172FPb both have TWO SECONDS TO BLACK

What size picofuse are on these boards? like to make a oder for them but don`t know witch one`s Iam looking for.

Your fuses are fine if they read 0.6 ohms.

The rating is usually 125V 3 Amp for this model.

They also sell kits on ebay that included c5707s, the picofuse, and fu9024s.

Search for

c5707 repair kit