Gateway FPD2185W

[bluto]

Re: Gateway FPD2185W

PlainBill and I have been discussing and have determined that this issue has something to do with the undercurrent sensing circuitry causing two seconds to black. Here is a picture of the area near T404 and the BIT3193.



As you can see the secondary of T404 takes a different path to ground from all the other small transformers. I am guessing that this is part of the undercurrent sensing circuitry.

The resistance of T404 is 215 ohm (primary) and .5 ohm (secondary)
The resistance of T403 is 215 ohm (primary) and .5 ohm (secondary)

[hoadle]

Re: Gateway FPD2185W

Last time I had Gateway FPD2185W the power light binking & monitor not on
I replace all capasistor & monitor working again
is been 4 month now still working final

[PlainBill]

Re: Gateway FPD2185W

That's teh best picture I've seen of the area, but it's still not good enough. Hopefully something with even better resolution will help. I've outlined the area of interest.

Also, try taking the picture from directly overhead, flash off, with the board next to a window or other source of natural light.

And it is not necessary to link to the attachment from the body of your post; just attaching it (so it appears as a thumbnail) works well for me.

PlainBill

[bluto]

Re: Gateway FPD2185W

I borrowed a different camera to try and get a better pic. Here it is. For some reason it got re-sized to ~418kb after uploading. The original was ~2.5mb. PlainBill please let me know if this is sufficient. I could email it to you directly if that would work better. I am hoping for a miracle here.

Otherwise, I am just about tired of messing with this display. I might have to rig a repair if nothing else avails. 4 out of 6 CCFLs can be that bad!

[Wrog]

Re: Gateway FPD2185W

A friend of mine has one that recently stopped working; he's going to send it my way to see if I can get it working again. Maybe we can compare measurements with the hopes of getting both up and running!

[PlainBill]

Re: Gateway FPD2185W

I borrowed a different camera to try and get a better pic. Here it is. For some reason it got re-sized to ~418kb after uploading. The original was ~2.5mb. PlainBill please let me know if this is sufficient. I could email it to you directly if that would work better. I am hoping for a miracle here.

Otherwise, I am just about tired of messing with this display. I might have to rig a repair if nothing else avails. 4 out of 6 CCFLs can be that bad!

That is an excellent picture. This might take a day or so; we've had a small household emergency and I'm going to be scrambling to get things working.

PlainBill

[PlainBill]

Re: Gateway FPD2185W

I borrowed a different camera to try and get a better pic. Here it is. For some reason it got re-sized to ~418kb after uploading. The original was ~2.5mb. PlainBill please let me know if this is sufficient. I could email it to you directly if that would work better. I am hoping for a miracle here.

Otherwise, I am just about tired of messing with this display. I might have to rig a repair if nothing else avails. 4 out of 6 CCFLs can be that bad!

Well, here you go. I've got a number of gaps I will need filled in.

Starting at the upper left, I've identified a trace (yellow) that seems to come from all transformers. I've traced it as far a R331 and R332. Where does it go from there?

Again, starting in the upper left I've identified a trace (teal) that is the end of the primary of T404. It seems to go to Q305 and C326, where does it go from there?

Still in the same area, I've labeled a trace Gnd? Is it indeed connected to ground?

On the lower left I've identified a trace (brown) that I believe comes from the return side of the secondary of T302. I've labeled it Return? Does it go the the corresponding transformer for the other CCFLs ? Is it connected to anything else?

Still on the lower left side I've identified a trace (blue) that is part of the voltage sense circuitry. It appears to go under JR301. Where does it go next?

On the lower right side I've identified a trace (puce) from the Isens input. I think I've traced it to R329. Where else does it go?

In the same area, I've also tentatively identified a trace that connects to R332 as Gnd. Is that correct?

On U303 I've labeled the clamp pin. I believe it is connected to the right end of a component that is identified as C321, but actually appears to be a resistor. Is that correct? And where else does it go?

Whew!!!

PlainBill

[bluto]

Re: Gateway FPD2185W

I finally got a chance to look at this again. Here are the answers and a further marked up picture:

Well, here you go. I've got a number of gaps I will need filled in.

Starting at the upper left, I've identified a trace (yellow) that seems to come from all transformers. I've traced it as far a R331 and R332. Where does it go from there?

R331 goes to top right of Q305 and C327
R332 goes to C327, JR303 and R317

Again, starting in the upper left I've identified a trace (teal) that is the end of the primary of T404. It seems to go to Q305 and C326, where does it go from there?

Goes to R329, C326 and Pin 15 U303 (Magenta)

Still in the same area, I've labeled a trace Gnd? Is it indeed connected to ground?

Yes

On the lower left I've identified a trace (brown) that I believe comes from the return side of the secondary of T302. I've labeled it Return? Does it go the the corresponding transformer for the other CCFLs ? Is it connected to anything else?

Yes goes to the corresponding transformer. Seems to be connected to ground

Still on the lower left side I've identified a trace (blue) that is part of the voltage sense circuitry. It appears to go under JR301. Where does it go next?

See attached image

On the lower right side I've identified a trace (puce) from the Isens input. I think I've traced it to R329. Where else does it go?

See above and attached image

In the same area, I've also tentatively identified a trace that connects to R332 as Gnd. Is that correct?

Yes

On U303 I've labeled the clamp pin. I believe it is connected to the right end of a component that is identified as C321, but actually appears to be a resistor. Is that correct? And where else does it go?

Yes it is a resistor. See attached image

Whew!!!

PlainBill

You're telling me!

[PlainBill]

Re: Gateway FPD2185W

OK, making a little progress on this. Rereading the thread helped to refresh my memory on what is going wrong. And not surprisingly, we may have been chasing the wrong trail. The inverter is designed as a constant current source. The inverter controller is designed to initially drive the CCFLs at full power, then reduce the output drive as the current rises to meet the design specs.

In this case, it appears the CCFLs never get full power. There are only a few possible causes. One is the over voltage protection circuit prevents the output from going high enough. We've eliminated that. Another is that the current sensing circuit is overly sensitive; the controller senses that it has reached the proper brightness level before all CCFLS are operating.

To test this theory, Bluto we (and by 'we' I mean you) are going to reduce the value of a resistor slightly by putting a larger resistor across it. In this case the target is R332, the 10K resistor (103) below and to the left of U303. For starters, try soldering a 100K resistor across it and see if it affects brightness of the CCFLs. If that doesn't make enough of a change, reduce the value to 47K, 22K, and even 10K.

PlainBill

[bluto]

Re: Gateway FPD2185W

I don't think that was the right resistor. I went all the way down to 470 ohm. No difference in CCFL brightness. Most of the time only the center light turns on and then two seconds to black. About one in every ten power on attempts, two of the three cclfs per bank will come on and stay on if there is a vga signal present. In this case removing the 470 resistor while the monitor is hot did not affect brightness. The ccfls stayed the same with only 2/3 burning per bank.

[bluto]

Re: Gateway FPD2185W

I take that back a little bit. In the time it took me to come upstairs and make the previous post and then go back downstairs to the shop, the CCFLs had turned themselves off. Now I get the outer two CCFLs on each bank lighting and then two seconds to black. I tried turning them on/off about 40 times and was unable to get them to stay on for more than 2 seconds. Not sure what to think about this monitor!

[PlainBill]

Re: Gateway FPD2185W

I take that back a little bit. In the time it took me to come upstairs and make the previous post and then go back downstairs to the shop, the CCFLs had turned themselves off. Now I get the outer two CCFLs on each bank lighting and then two seconds to black. I tried turning them on/off about 40 times and was unable to get them to stay on for more than 2 seconds. Not sure what to think about this monitor!

I understand exactly. I keep feeling like I'm missing something obvious.

Your tests indicate that the inverter controller isn't limiting the output voltage. Which makes me wonder what is?

PlainBill

[bluto]

Re: Gateway FPD2185W

It might be time for me to give up on this monitor...

[PlainBill]

Re: Gateway FPD2185W

It might be time for me to give up on this monitor...

Off the top of my head, I come up with only a limited number of reasons for this problem.

1. Insufficient voltage to the inverter.

2. Insufficient drive to the transformers

3. Shorted turn(s) on the primary of one transformer.

4. OVP, OLP, or current regulation wrong.

5. Defective inverter controller.

OK, I admit it, I'm feeling lazy tonight. I don't feel like rereading the whole thread. Did this occur suddenly, or was it a gradual decline?

At this point all I can think of to try would be to check the voltage to the inverter, do a ring test on the transformers, and use an oscilloscope to look at the drive waveform.

PlainBill

[bluto]

Re: Gateway FPD2185W

I am assuming that it was a gradual decline. The monitor was given to me by a colleague to fix. I was going to do a simple recap for him and give it back. But when that didn't work out he turned it over to me. I have replaced the lamps and most recently the 4 drive transistors. It might be also a good idea to start looking for ones with broken screens, since this one is such a bear

[PlainBill]

Re: Gateway FPD2185W

I am assuming that it was a gradual decline. The monitor was given to me by a colleague to fix. I was going to do a simple recap for him and give it back. But when that didn't work out he turned it over to me. I have replaced the lamps and most recently the 4 drive transistors. It might be also a good idea to start looking for ones with broken screens, since this one is such a bear

That may be the best approach.

PlainBill

[whitejohnny71]

Re: Gateway FPD2185W

@Bluto:

I just repaired one of these; it had the one-second-on backlight issue as well. The caps were good; this was a later year model I guess. When I would power it on, in dim light I could see arcs all over the inverter transformers and output traces/joints. Looked like mine had dry solder joints all over the high side and burnt ccfl leads.
First I reworked the board, then I repaired the ccfl leads. I still got 2 or 3 bulbs on each side lasting a second when powered on. I noticed there was a lotta volts between the lcd chassis and the supply chassis, and that when trying to measure the ground differential, my meter would cause the unit to power off and reset. So I grounded the two chassis together; that fixed it. When you repair the bulb connections, make sure to use plenty of heat shrink insulation, or get the proper replacement ends. Make sure to rework under the white caulk/gunk on the board too. I added a ground strap, that did it.

Originally I used electrical tape and kept what was left of the little white rubber bulb ends; it let too much electricity to the metal reflector and chassis.
I noticed the ground differential the old fashion way -lol-!!!

Its been running for an hour plus now, no flicker or anything.

Good luck, if you're still working with it.

[whitejohnny71]

Re: Gateway FPD2185W

Ah HAH!!! If you still can't get rid of the flicker (mine came back) here's some info and a possible fix for it... Worked for me anyway.

There are six lamps. One side of each lamp connects to a bigger transformer. The other side connects to a smaller transformer, which appears to be only for sensing (although I could be wrong). The circuit is in two halves, 3 lamps on each big transformer. However the protection sensing circuit is not split evenly - if you follow the traces you find that the first lamp (board traces/bottom up, ccfl connectors to the right) is by itself, and the other 5 connect together (follow traces between small transformers).

How does this help?

I swapped the returns so that the second bulb (small black wire) feeds the single lamp sensing circuit and the first one (small yellow) feeds the five piece circuit. Turns out the first bulb was pretty worn, and was making the protection trip.

Now its perfectly stable!!!! Yay, so happy....

[PlainBill]

Re: Gateway FPD2185W

Ah HAH!!! If you still can't get rid of the flicker (mine came back) here's some info and a possible fix for it... Worked for me anyway.

There are six lamps. One side of each lamp connects to a bigger transformer. The other side connects to a smaller transformer, which appears to be only for sensing (although I could be wrong). The circuit is in two halves, 3 lamps on each big transformer. However the protection sensing circuit is not split evenly - if you follow the traces you find that the first lamp (board traces/bottom up, ccfl connectors to the right) is by itself, and the other 5 connect together (follow traces between small transformers).

How does this help?

I swapped the returns so that the second bulb (small black wire) feeds the single lamp sensing circuit and the first one (small yellow) feeds the five piece circuit. Turns out the first bulb was pretty worn, and was making the protection trip.

Now its perfectly stable!!!! Yay, so happy....

Good job. I've agonized over that circuit and pretty much came to the same conclusion. You have confirmed it.

The classic inverter design senses the current through all the lamps and uses that to set the output level. A separate circuit monitors current through individual lamps. This design uses the current through one CCFL to set the current for all six.

PlainBill

[whitejohnny71]

Re: Gateway FPD2185W

The classic inverter design senses the current through all the lamps and uses that to set the output level. A separate circuit monitors current through individual lamps. This design uses the current through one CCFL to set the current for all six.

PlainBill

Yeah, I'm just figuring that out now; I've been doing motherboards for awhile now, and on so many laptops where the screen doesn't work its a bad connection to the bulb - so I'd gotten used to looking for that. Recently I started doing LCD monitors and Flat-Panel TV's (funny how people will pay more to fix their TV then their computer isn't it?) and haven't really done enough homework on the basic circuit theory. I was referring to a pair of Acer monitor schematics when I noticed the 5 to 1 thing.

Do you have, or can you point me to some basic reference schema for the protection side of it? I understand how the pwm chip feeds switching fets into transformer, just a little fuzzy on the sensing of over voltage and over current. I have attached one of the schema's I'm working with, do most multiple tube backlights implement the over voltage with a string of transistors like this one (Q502-Q505) - looks like all 4 co-operate to hold Q501 off right? And when Q501 turns on by the pull up resistor it trips the protection?