Dell 1702FP won't power on (lights just flash)

[petewill]

Hello,
I have searched this forum and the internet for hours trying to find my solution. Since I can't find anything I thought I'd post here since there seems to be a lot of very smart and helpful people.

I have a Dell 1702FP that won't turn on. It has the same flashing light pattern as monitor in this video: http://www.youtube.com/watch?v=vUmX2E6bzf4. I found a post on Instructables.com here: http://www.instructables.com/id/FREE...y-Dell-1702FP/ that said to replace the capacitors. I replaced the two recommended ones and it didn't work. I went out and bought a multimeter that tests capacitance and all the capacitors have tested ok. After that I looked around the board and found that there seems to be damage on the Samsung SIC1803 board. Does anyone have any idea what I can replace the brown (I think they are capacitors) pieces with? Do you think that is the problem? Can I test anything else?

Any help is appreciated. I'm very new at this but I'd love to fix my monitor if possible.

Thanks!

[retiredcaps]

Re: Dell 1702FP won't power on (lights just flash)

1) Please post pictures of your power and logic board (like your excellent clear focused inverter board one).

If your power LED is not on solid green, this could be bad caps causing unstable power (probably 5V DC) to the logic board. Or there is something wrong on the logic board.

Either way, post the pictures and we can suggest test points.

2) Did cap C5 look like that? That is, off the board?

[PlainBill]

Re: Dell 1702FP won't power on (lights just flash)

One quick test you can do is unplug the cable that's connected to CN1 (do this with the monitor unplugged ). If the monitor power LED now works normally (of course you won't see anything on the display) the inverter is the cause.

NOW it looks like C5 may be damaged; it's kind of hard to tell. If that is the case, and the monitor responded as I described with the inverter disconnected, the odds are Q7 and / or Q8 are shorted.

PlainBill

[petewill]

Re: Dell 1702FP won't power on (lights just flash)

Thank you both for the quick replies! I really appreciate the help. I have been getting pretty frustrated with my lack of knowledge and understanding I was just about to give up. I have hope again!

Retiredcaps,
1) I have attached two more pictures of what I hope are the logic board. I was hoping you wouldn't ask for them because it will show my very poor soldering. I read online that to test capacitors with a capacitance meter you need to remove one of the connections from the board. So when you see lopsided, poorly soldered capacitors that's what happened to them. All the ones I tested, tested fine though.

2) No C5 was not off the board like that. I cut the adhesive in an attempt to see the capacitance rating so I could replace it. I couldn't find anything except the same cryptic numbers on the other side though. It did have that brown looking residue around it before I touched it.

PlainBill,
Thank you very much for the suggestion. I removed the CN1 connection and the lights are now staying solid green instead of flashing as they were in that video. I have posted a picture of the lights in case it's relevant.



Ok, so from those results it appears it is something in the inverter that is the problem. This may seem like a stupid question but what are Q7 and Q8? Is there any way I can test if they are shorted? If so do I need to remove them from the board? I have uploaded a few more pictures of the inverter from different angles if that helps at all.

Thanks again to both of you for all your help!! Hopefully I can get this up and running again.

Pete

[retiredcaps]

Re: Dell 1702FP won't power on (lights just flash)

This may seem like a stupid question but what are Q7 and Q8? Is there any way I can test if they are shorted? If so do I need to remove them from the board?

Q7 and Q8 are PCB designations. See attached pic and what is circled in red.

To test Q7 and Q8, you can do this "in circuit" (no need to desolder) by following the instructions at section 2

https://www.badcaps.net/forum/showpo...0&postcount=13

Report your findings.

PS. You might as well test Q14 and Q15 at the same time and report those findings as well.

[jetadm123]

Re: Dell 1702FP won't power on (lights just flash)

Also, if Q7 or Q8 short out, it's likely that fuse F1 will also blow.

[Lumberjack777]

Re: Dell 1702FP won't power on (lights just flash)

You also need to test that fuse located at F1 for continuity. Soldering just takes a little practice. Here's a great soldering tutorial on YouTube. http://www.youtube.com/watch?v=I_NU2ruzyc4

Edit: LOL Jetadm. Great minds.

[PlainBill]

Re: Dell 1702FP won't power on (lights just flash)

You also need to test that fuse located at F1 for continuity. Soldering just takes a little practice. Here's a great soldering tutorial on YouTube. http://www.youtube.com/watch?v=I_NU2ruzyc4

Edit: LOL Jetadm. Great minds.

Not that great. If the fuse were open unplugging the cable wouldn't have had any effect.

The sequence goes like this: The power supply comes up, the controller on the signal card turns on the power LED and the backlights. Because the inverter has a short, this overloads the power supply, which shuts down. The controller no longer is trying to turn on the inverter, so the power supply comes back up, the lights come back on, etc.

This is one of those 'clever' designs where the fuse rating is much higher than the power supply can provide.

PlainBill

[petewill]

Re: Dell 1702FP won't power on (lights just flash)

Well, I tested the mosfets as suggested and I have posted my results below. I wasn't exactly sure what the pin order was so hopefully I did it correctly. I have attached an image to clarify what pin order I used. Also, I couldn't figure out how to set my multimeter to 200 ohms. I looked in the manual and online but it seems I could only set the scale (M, k or just ohms). Hopefully that will be ok. All the mosfets have the same identification on them (“C5103” and “Q A” on the next line) so it appears than two of them are defective (just as retiredcaps suspected).


Q7 Test
a) black on pin 1- red on pin 2 - .456 k ohms
b) black on pin 1- red on pin 3 – 1.261 k ohms
c) black on pin 2- red on pin 3 – .729 k ohms

Q8 Test
a) black on pin 1- red on pin 2 - .456 k ohms
b) black on pin 1- red on pin 3 – 1.257 k ohms
c) black on pin 2- red on pin 3 – .726 k ohms

Q14 Test
a) black on pin 1- red on pin 2 - .457 k ohms
b) black on pin 1- red on pin 3 - .457 k ohms
c) black on pin 2- red on pin 3 - .5 ohms

Q15 Test
a) black on pin 1- red on pin 2 - .457 k ohms
b) black on pin 1- red on pin 3 - .457 k ohms
c) black on pin 2- red on pin 3 - .5 ohms

I also tested the fuse and here is the result:
F1 Test
.4 ohms

So now I have a few more questions. Which mosfets are the defective ones. Can they be replaced and if so what part should I replace them with? Should I test/replace anything else before I replace the mosfets?

Thanks again for all the help!

[PlainBill]

Re: Dell 1702FP won't power on (lights just flash)

Well, I tested the mosfets as suggested and I have posted my results below. I wasn't exactly sure what the pin order was so hopefully I did it correctly. I have attached an image to clarify what pin order I used. Also, I couldn't figure out how to set my multimeter to 200 ohms. I looked in the manual and online but it seems I could only set the scale (M, k or just ohms). Hopefully that will be ok. All the mosfets have the same identification on them (“C5103” and “Q A” on the next line) so it appears than two of them are defective (just as retiredcaps suspected).


Q7 Test
a) black on pin 1- red on pin 2 - .456 k ohms
b) black on pin 1- red on pin 3 – 1.261 k ohms
c) black on pin 2- red on pin 3 – .729 k ohms

Q8 Test
a) black on pin 1- red on pin 2 - .456 k ohms
b) black on pin 1- red on pin 3 – 1.257 k ohms
c) black on pin 2- red on pin 3 – .726 k ohms

Q14 Test
a) black on pin 1- red on pin 2 - .457 k ohms
b) black on pin 1- red on pin 3 - .457 k ohms
c) black on pin 2- red on pin 3 - .5 ohms

Q15 Test
a) black on pin 1- red on pin 2 - .457 k ohms
b) black on pin 1- red on pin 3 - .457 k ohms
c) black on pin 2- red on pin 3 - .5 ohms

I also tested the fuse and here is the result:
F1 Test
.4 ohms

So now I have a few more questions. Which mosfets are the defective ones. Can they be replaced and if so what part should I replace them with? Should I test/replace anything else before I replace the mosfets?

Thanks again for all the help!

You did well. Q14 and Q15 are shorted collector-emitter. They are available from Digi-Key as 2SC5103TLQCT-ND for $1.14 each. They only have about 8400 on hand.

Before placing any orders, there are a few more things to test. Directly below C3 you have D3 and D13; and below them are Q6 and Q13. Check the resistance across D3 and D13. Also check all three combinations of the leads of Q6 and Q13 just like you tested Q14 and Q15.

PlainBill

[retiredcaps]

Re: Dell 1702FP won't power on (lights just flash)

Q14 Test
c) black on pin 2- red on pin 3 - .5 ohms

Q15 Test
c) black on pin 2- red on pin 3 - .5 ohms

Remove Q14 and Q15 (desolder them from the board) and retest pin 2 to 3 to verify. If they are indeed bad, you have to remove them anyway for the replacements.

If you can't set your multimeter to 200 ohms, you probably have an auto-ranging multimeter.

[petewill]

Re: Dell 1702FP won't power on (lights just flash)

Well, I don't know if I'm cut out for electronics repair. It took me about an hour to finally figure out how to remove the mosfets and in the process I managed to break off L2 so I had to solder that back on! I sure hope I learn from all this…

I did the other tests suggested but I don't know what they mean Here are my results:

D13 Test
Fluctuating between .5 and .3 ohms

D3 Test
.793 k ohms

Q13 Test
a) black on pin 1- red on pin 2 – 10.65 M ohms
b) black on pin 1- red on pin 3 – 25.86 M ohms
c) black on pin 2- red on pin 3 – 6.06 M ohms

Q6 Test
a) black on pin 1- red on pin 2 – 6.32 M ohms
b) black on pin 1- red on pin 3 – 21.55 M ohms
c) black on pin 2- red on pin 3 – 6.12 M ohms

I didn't get any reading (it only said OL) when I tested pin 2- red on pin 3 on both mosfets after I removed them. Am I doing something wrong? Do I need to test a different way than before?

Also, do you think I need to test C14 and C5? I don't know what capacitance they are but my capacitance meter will only go up to 200 uf which I'm guessing isn't high enough. If you do recommend I test them is there any other way besides a capacitance meter? Or should I just replace them anyway?

Thanks!

[retiredcaps]

Re: Dell 1702FP won't power on (lights just flash)

I managed to break off L2 so I had to solder that back on!

Components beginning with the letter "L" are inductors.

D13 Test
Fluctuating between .5 and .3 ohms

D3 Test
.793 k ohms

To test a diode, set your multimeter to the diode test function. Put red on one side and black on the other. Record reading. Now reverse the probes and record the new reading.

A good diode should measure between 0.3 and 0.7V in one direction and 0L in the other. Report your findings.

Q13 Test
a) black on pin 1- red on pin 2 – 10.65 M ohms
b) black on pin 1- red on pin 3 – 25.86 M ohms
c) black on pin 2- red on pin 3 – 6.06 M ohms

Q6 Test
a) black on pin 1- red on pin 2 – 6.32 M ohms
b) black on pin 1- red on pin 3 – 21.55 M ohms
c) black on pin 2- red on pin 3 – 6.12 M ohms

Q13 and Q6 are good.

I didn’t get any reading (it only said OL) when I tested pin 2- red on pin 3 on both mosfets after I removed them.

These two removed transistors are *likely* good if they read 0L. 0L means beyond the range that the multimeter can read. I say *likely* because a resistance test isn't an all inclusive test. I tested 3 new good c5707 transistors and they measure 0L between 2-3.

When you measured 0.5 ohms "in circuit", it is likely that some other component or the circuitry around it caused the low ohm reading. By removing it "out of circuit", then the reading is accurate.

So as long as you tested pins 2-3 for resistance and got 0L, that suggests the 2 transistors are fine.

That means something else around that area might be shorted?

Also, do you think I need to test C14 and C5? I don’t know what capacitance they are but my capacitance meter will only go up to 200 uf which I’m guessing isn’t high enough.

Testing for uF and testing for ESR are two totally different things. I don't know of any digital multimeter (even the high end ultra expensive Flukes) that tests ESR (equivalent series resistance). You need a specialized ESR meter to test for ESR.

A cap can be uF correct, but have high ESR. For example, a 1000uF 10V cap might measure 999uF on your Iso-tech multimeter, but the cap's ESR could 21 ohms (which is high).

[petewill]

Re: Dell 1702FP won't power on (lights just flash)

I tested the diodes the correct way this time. Here are my results:

D3 Test
Red to Black - .479 v
Black to Red - .124 v

D13 Test
Red to Black - .0 v
Black to Red - .0 v

It seems like maybe I should replace the diodes? Do you know what value they are and where I could purchase them? The part says “S3 22” and it's written like this:

S3
22

What do you think my odds of this thing coming back to life if I just replace the diodes? Have you had monitors with diodes that failed? Also, I can't get my mind of those capacitors. They have lots of orange/brown residue where they meet the board. Maybe if I replace those and the diodes it would work?

This monitor is pretty old (2002) so I'm wondering if it would be better to save my money and look into buying something new… thoughts?

Thanks again for all your help!

[PlainBill]

Re: Dell 1702FP won't power on (lights just flash)

I tested the diodes the correct way this time. Here are my results:

D3 Test
Red to Black - .479 v
Black to Red - .124 v

D13 Test
Red to Black - .0 v
Black to Red - .0 v

It seems like maybe I should replace the diodes? Do you know what value they are and where I could purchase them? The part says “S3 22” and it's written like this:

S3
22

What do you think my odds of this thing coming back to life if I just replace the diodes? Have you had monitors with diodes that failed? Also, I can't get my mind of those capacitors. They have lots of orange/brown residue where they meet the board. Maybe if I replace those and the diodes it would work?

This monitor is pretty old (2002) so I'm wondering if it would be better to save my money and look into buying something new… thoughts?

Thanks again for all your help!

D13 is bad; D3 is good. It is probably a 40V 2A Schottky diode in a DO-214AA package such as the SMB240 or the SK24-TP (same specs, different manufacturer). They are about $.55 each.

The odds are very good it will come back to life if the shorted diode is replaced and the transformer leads are resoldered.

PlainBill

[retiredcaps]

Re: Dell 1702FP won't power on (lights just flash)

Have you had monitors with diodes that failed?

Yes. Diodes like any other component can go bad.

Also, I can't get my mind of those capacitors. They have lots of orange/brown residue where they meet the board.

That was likely white glue back in 2002 that has turned brown due to heat and aging. You can leave it alone or scrape it off.

[petewill]

Re: Dell 1702FP won't power on (lights just flash)

Great thanks for the help. I will try replacing the diode. I'll post back the results.

Thanks again!

[petewill]

Re: Dell 1702FP won't power on (lights just flash)

Well, you guys are geniuses… the monitor is working again!!!! I have to admit I was pretty skeptical but I decided to try replacing the diode. I was ready to throw the monitor in the trash out of frustration and the way it was cluttering up my room, but I really didn't feel right about giving up after all the help you gave me. I was out of town for work for a while but I finally got around to ordering the part that PlainBill suggested. I just replaced it tonight and what do you know, the monitor turned right on! THANKS again for all your help!

[kajubi]

Re: Dell 1702FP won't power on (lights just flash)

i have just repaired the same monitor with the same problem it took me only 2 minutes to get to the problem it was just a capacitor 100/16 i replaced with 470/16

[selldoor]

Re: Dell 1702FP won't power on (lights just flash)

i have just repaired the same monitor with the same problem it took me only 2 minutes to get to the problem it was just a capacitor 100/16 i replaced with 470/16

That was lucky? - well done - remember if one cap has gone, others are the same age in the same environment and may also be failing.