Dell E172fpb

[PlainBill]

Re: Dell E172fpb

well; I did read all 18 pages. The found one very good picture but it is too small to see all the line tracing. I need a super large image of a good board showing all 4 transistors.

I checked the fuse for continuity and it shows continuity? is that the way the fuse should be tested?

Yes.

PlainBill

[techbrat]

Re: Dell E172fpb



if this picture was a little bigger and zoomed in a lot closer. I could see the detailed line tracing!

[techbrat]

Re: Dell E172fpb

well; I did read all 18 pages. The found one very good picture but it is too small to see all the line tracing. I need a super large image of a good board showing all 4 transistors.

I checked the fuse for continuity and it shows continuity? is that the way the fuse should be tested?

[PlainBill]

Re: Dell E172fpb

I had this problem on my dell 17" e172fpb too. The monitor would work for 2 seconds showing the bios motherboard booting and then shutoff and the power light turned orange.

replaced all 4 transistors with the oem japan transistors and it blew the transistors immediately

then I went to radio shack and used a NPN tipp 3055

I saw the back-light come on very bright white and shutoff.

Now the back-light does not come on any longer

It never came back on after that! I tried a bunch of NPN tipp 3055 today and the back-light did not come on period. I pretty much give up on this monitor.

The traces have peeled off the board next to the transistors and it is hard to remember the trace routing when soldering

does anyone have a picture of the traces?

Read the other 18 pages of this thread. There may be pictures of both sides of the board on one of the pages. With luck all you've done is blow a fuse. Or you may have destroyed more than just the traces.

PlainBill

[techbrat]

Re: Dell E172fpb

I had this problem on my dell 17" e172fpb too. The monitor would work for 2 seconds showing the bios motherboard booting and then shutoff and the power light turned orange.

replaced all 4 transistors with the oem japan transistors and it blew the transistors immediately

then I went to radio shack and used a NPN tipp 3055

I saw the back-light come on very bright white and shutoff.

Now the back-light does not come on any longer

It never came back on after that! I tried a bunch of NPN tipp 3055 today and the back-light did not come on period. I pretty much give up on this monitor.

The traces have peeled off the board next to the transistors and it is hard to remember the trace routing when soldering

does anyone have a picture of the traces?

[PlainBill]

Re: Dell E172fpb

Hi Mohonri
Very Interesting
Are you saying that you are testing when Monitor Powered On???
Also how can you attain a Voltage reading on (Diode Test) settings???
Thanks
Bob

I though most electronics techs knew this. The diode test function on a dmm works by applying a voltage to one end of a resistor, the other end of the resistor is connected to the + lead. The number displayed is the voltage across the leads. Since the voltage applied and the value of the resistor vary, it is difficult to determine precise information on the diode (or transistor) characteristics. In theory, a silicon diode conducts at 0.7 volts. A DMM diode test can report anything from .5 volts to more than .8 volts, depending on the meter design and the type of diode. You can't do the test with power on.

I prefer to check transistors (and diodes) for shorts by using the 200 ohm scale. This should be the same for all meters (within the accuracy limits of the meter). The Ohms scale will not detect an open transistor, but it was designed not to.

PlainBill

[Bobdee]

Re: Dell E172fpb

One tip I've learned: The transistors *can* be tested in-circuit by using the "diode" setting on my multimeter. Measure from base to emitter and from base to collector. Both should be between 0.5V to 1.0V. Failed transistors show a short.

Hi Mohonri
Very Interesting
Are you saying that you are testing when Monitor Powered On???
Also how can you attain a Voltage reading on (Diode Test) settings???
Thanks
Bob

[Mohonri]

Re: Dell E172fpb

Well, I'm now up to six or seven of these monitors. One of them had a failed FU9024N, but all had failed C5707 transistors. Replacing the failed transistor and resoldering the tranformers has done the trick every time.

One tip I've learned: The transistors *can* be tested in-circuit by using the "diode" setting on my multimeter. Measure from base to emitter and from base to collector. Both should be between 0.5V to 1.0V. Failed transistors show a short.

Also, a hot iron is important. If your iron isn't hot enough, the traces can come up.

The E173FPb has the same issue as the E172FPb.

As others have said (over and over again, but the question still comes up) you MUST resolder the transformers.

I personally have seen no bad caps, but maybe I've been lucky so far

[Bobdee]

Re: Dell E172fpb

Swapping transistors is not sufficient in my case. After 3 days, the transistors got shorted.

Hello Gina0602
You must resolder the 4 Inverter transformers, these are the probable cause for the failure of the transistors in the first place
They usually have ring cracks that are hard to see with the naked eye
Resolder all four
Possibly only one of the new transistors has failed, so one of your old ones that is good can replace it and check inverter fuse if there is one
Bob

[PlainBill]

Re: Dell E172fpb

Swapping transistors is not sufficient in my case. After 3 days, the transistors got shorted.

Have you resoldered the transformer leads? That is a common problem. Also, have you replaced the capacitors, especially those in the inverter section?

PlainBill

[gina0602]

Re: Dell E172fpb

Thanks all for your help...

I tested the transistors Q759 and Q760 were shorted, I have swapped these, and the monitor now works great!

Once again, Thanks to all who helped!

Swapping transistors is not sufficient in my case. After 3 days, the transistors got shorted.

[xtraelectronics]

Re: Dell E172fpb

Also nobody mentioned that the C5707 is listed in the spec sheet as a "high speed switch". The reason the TIP41C's are running so hot is because they are not designed to operate this way. Look at the PDF spec sheets when deciding what transistors to use as replacements. C5707: https://cdn.badcaps-static.com/pdfs/...964cb690e1.pdf
TIP41C: https://cdn.badcaps-static.com/pdfs/...3d809d111d.pdf

NTE cross reference: http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search

[mbates14]

Re: Dell E172fpb

also its amazing after replacing JUST the transistors you guys have working monitors. most of you are failing back out within a short period of time:

Word of advice:

Check the shottkey clamps D751,D761. they 90% of the time will short when the base current surges during the transistors "shorting" stage before shutdown.

This helps limit the base current on the output transistors, if this diode is bad, the unit will run.. but not for long....

Diode SB360

[EGuevarae]

Re: Dell E172fpb

well, i bought the kit on ebay and my monitor is alive! less than $10 in parts - sure beats buying a new invertor board or monitor.

FYI, i got the kit here:

http://cgi.ebay.com/ws/eBayISAPI.dll...m=220486136668

Don't forget to resolder the transformer solder points or else you will be working in the unit again very soon....

[weefa]

Re: Dell E172fpb

well, i bought the kit on ebay and my monitor is alive! less than $10 in parts - sure beats buying a new invertor board or monitor.

FYI, i got the kit here:

http://cgi.ebay.com/ws/eBayISAPI.dll...m=220486136668

[PlainBill]

Re: Dell E172fpb

sorry in advance guys, but when i have the time i'll read through the 19 pages of this thread.

my monitor powers on for a few seconds and shuts off. from what i could gather is this the kit that i need to fix the problem?

http://cgi.ebay.com/ws/eBayISAPI.dll...m=220476282873

Yes, that should do it. Also, resolder all pins on both transformers in the inverter.

PlainBill

[weefa]

Re: Dell E172fpb

sorry in advance guys, but when i have the time i'll read through the 19 pages of this thread.

my monitor powers on for a few seconds and shuts off. from what i could gather is this the kit that i need to fix the problem?

http://cgi.ebay.com/ws/eBayISAPI.dll...m=220476282873

[Richie_asg1]

Re: Dell E172fpb

Have just picked up a Dell - E151FPb for rework.

Aparently "works ok for a bit - but have to keep smacking it"

Exhibited classic Transformer cracked solder joints.

Resoldered all inductors as there was signs of rings around more than one.

Works fine now.

This NASA website is great for good practice and faults in soldering -
http://workmanship.nasa.gov/lib/insp...uirements.html

[AquaticEarth]

Re: Dell E172fpb

Update: After second power-on, the monitor failed again with the same on-off cycle problem. This time I took the advice from earlier posts and resolder the PCB. Now it's back to working condition.

[AquaticEarth]

Re: Dell E172fpb

Got a BENQ FP531 LCD which use exactly the same PCB with the same problem as described in this thread. Just replaced Q759, Q760, Q740 and Q739 with four 2sc5706 from local electronic store for NT$15 each (USD0.46) this afternoon and everything went ok. Thanks for all message contributors here, you guys are great!