Gateway FPD2185w- backlight dies after 3 seconds

[Curt Palme]

Hi guys, new to the forum, but a fairly experienced electronics board level tech here.

I've recently gotten into repairing flat screens, and am cutting my teeth (and pulling out my hair) as the learning curve goes..

I've got about 50 computer monitors through the door here, and have been about 70% successful overall, and my junk bin is full of garbage Chinese capacitors.

Anyways, onto the current issue:

I've got two Gateway 21" widescreen monitors with identical problems. Both lose the backlight about 2-3 seconds after powerup. I can still see the video present on the screens with a flashlight, so it's not the screen itself.

What I've done so far:

Swapped LCD panels and backlights between units, no change on either set.
Disconnected the LCD panel and backlight completely, I still get shutdown.
Pulled out the output transformer one at a time and then both, still get shutdown.
I scope the driver and output of the switching transistors, and I can see that I lose the drive from the BIT3193G switching chip.
I've cooled the chip with spray, the shutdown time is constant.
I've measured all pins on the 3193G chip, and it appears that the problem could be internal to the chip, so I've ordered 4 on eBay.

One last thing that had me chasing the PC board: I thought I smelled corona if I quickly powered the set up and down a few times, but I am probably mistaken, as I thought maybe leaking HV off one transformer (or internally in the transformer) would cause that smell and an overload condition, shutting the chip down, but removing the transformers seems to have eliminated that train of thought.

Any other ideas before the chips get here in a week or so?

BTW, some of you might be interested in what I do for a living, this LCD thing is a sideline. Check out www.curtpalme.com for a peek into old school CRT technology from the 80s and 90s that could do past 1080p before that consumer standard was even set. I'm happy to answer questions, so feel free to email me via the site.

Thanks!
Curt

[Dgtech]

Re: Gateway FPD2185w- backlight dies after 3 seconds

Welcome, welcome, and welcome! I always enjoy meeting another tech. I hope that chip works out for you. I first have to ask though, if both units had exactly the same problem, how could it be conclusive that swapping one panel for another will produce anything different if both pannels were the issue with each monitor? Of course a tech like youself knows about caps, fuses and solder joints. The joints on some of the transformers have had issues in the past. Some of them have looked good but didnt work and just needed a reflow. If you could take pictures of the inverter board and post them, we can all assist you more in this task.

[Dgtech]

Re: Gateway FPD2185w- backlight dies after 3 seconds

I forgot to mention, the circuit wants to power up the CCFL's. When it cannot within a few seconds, the circuit shuts down. This may be happening to both monitors due to one bad CCFL. I had an IBM monitor with the same symptoms that had 4 CCFL's in it (2 on top of pannel and 2 on bottom). Only one of the lamps on the bottom circuit was burned out. The circuit wanted to see higher current. When this didnt happen, it shut down.

There are many more things that causes this condition and you will find it under "two seconds to black" in this forum.

[PlainBill]

Re: Gateway FPD2185w- backlight dies after 3 seconds

The problem you are seeing is called 'two seconds to black'. There are a number of possible causes. Briefly, most inverters monitor voltage across and current through each CCFL. If any are out of spec, the inverter shuts down.

In general, there are three possible causes:

1: A CCFL or it's associated wiring is defective - broken tube, broken wire, short to the metal are all common causes.

2. The inverter is not providing enough voltage to drive the CCFL. This is usually due to a problem with a transformer (open or shorted turns).

3: The protection circuit is triggering a shutdown due to a faulty component; it's sensing a fault when none exists.

The best way to troubleshoot this is to take a known good CCFL and hook it in turn to each output of the 'sick' inverter while leaving the original CCFLs connected to the other outputs. If it fails to light (or does not reach full brightness) on one output, it's a type 2 problem. If the backlights stay on only when it is connected to a certain output, it is a type 1 problem. And if the problem persists, it is a type 3 problem.

If it is a type 3 problem, attach good pictures of the front and back of the inverter, as well as the part number of the inverter controller (a 16-20 pin IC). See my signature for information on attaching pictures.

PlainBill

[Curt Palme]

Re: Gateway FPD2185w- backlight dies after 3 seconds

Thanks for the info. I agree, it could be that both sets hvae backlight /CCFL issues.

I also forgot to post that I did check all caps and scoped the power supplies on both sets, and both were right on the money.

It's tempting to buy a used working monitor off ebay just to isolate the problem, but I'll hold off for now, and will dive into this again next week.

Also, another thought occurred to me: Does the protection circuit sense opens as well as shorts? Regardless if the CCFLs are connected, the shutdown time does not change at all. I figured if there was an overcurrent situation happening on the units, I'd eliminate that by disconnecting them, but if the protection circuit also senses an open circuit condition, then I'm not eliminating the CCFL by disconnecting it.

[alexanna]

Re: Gateway FPD2185w- backlight dies after 3 seconds

Yes some can and most do sence opens.
Dose your junk pile have any broken or dammaged lcds?If so salvage the good ccfls,That way you will have a good test set.
Al.

[Curt Palme]

Re: Gateway FPD2185w- backlight dies after 3 seconds

I am getting about 10 monitors a week in. I am stockpiling known working parts, but of course I have nothing in stock currently that fits those 6 pin Gateway connectors. Figures!

[PlainBill]

Re: Gateway FPD2185w- backlight dies after 3 seconds

I am getting about 10 monitors a week in. I am stockpiling known working parts, but of course I have nothing in stock currently that fits those 6 pin Gateway connectors. Figures!

You have to be adaptable to prevail in the modern world. Or in this case, creative. I'm not going to go digging through the various threads to find pictures of a Gateway FPD2185w inverter, but think about this idea.

Take the panel from monitor 2. Position it so you can hook one CCFL connector from it to the inverter in panel 1. Leave the rest of the CCFLs in panel 1 hooked up. Turn on panel 1. Does the CCFL in panel 2 light up? If so, unplug that CCFL and plug another into panel 1. Working this way, you should be able to establish that all CCFLS in panel 2 light at equal brightness, or that one (or more) does not.

This is tedious (or exciting if you forget to unplug the monitor), but you will establish if all CCFLS in panel 2 appear to be working properly. Of course, you will also want to verify that all inverter outputs are working properly.

PlainBill

[Curt Palme]

Re: Gateway FPD2185w- backlight dies after 3 seconds

Good point Bill, I'll try that. AS I said, it is challenging cutting my teeth on these, different from the CRTs that I've worked on for 15 years, but at the same time frustrating when you spend 2 hours on something you can only resell for $75.

Thanks again!

[smason]

Re: Gateway FPD2185w- backlight dies after 3 seconds

I know you're an experienced tech, but I'll mention this anyway:
Did you *thorougly* check the capacitors? That model is notorious for bad caps, particularly the 8 470@25s that are all grouped together.

[PlainBill]

Re: Gateway FPD2185w- backlight dies after 3 seconds

Good point Bill, I'll try that. AS I said, it is challenging cutting my teeth on these, different from the CRTs that I've worked on for 15 years, but at the same time frustrating when you spend 2 hours on something you can only resell for $75.

Thanks again!

I guess it's a matter of perspective. I take a monitor that didn't cost me anything, add $10 in parts and 1 to 2 hours of time I would otherwise spend playing solitaire and get a monitor I can sell for $60 (in the case of the FPD2185w I'd go for $90). That puts $50 in my pocket and gives my claim I'm not a washed up old fossil some credibility.

PlainBill

[Dgtech]

Re: Gateway FPD2185w- backlight dies after 3 seconds

Each monitor/TV is learning experience is worth more than a price for any one unit. The way I look at it is, most of these problems and circuits are repetative. Make a checklist of the common failures with LCD monitors and spend extra time with the others. About 70% of my repairs were problems caught on a visual inspection. Maybe 25% were harder problems to find but still fixable. The rest (5%) were either scrapped for parts due to cost to repair. Even then sometimes I have eaten the cost just for pride's sake.

[smason]

Re: Gateway FPD2185w- backlight dies after 3 seconds

I guess it's a matter of perspective. I take a monitor that didn't cost me anything, add $10 in parts and 1 to 2 hours of time I would otherwise spend playing solitaire and get a monitor I can sell for $60 (in the case of the FPD2185w I'd go for $90). That puts $50 in my pocket and gives my claim I'm not a washed up old fossil some credibility.

PlainBill

I agree! I got 6 free bad ones, the first 2 that I chose to repair were tough dogs that turned out un-repairable (microcontrollers) and I spent more time than they were worth, but I learned a lot. The next one was the Gateway 2185w, in pristine physical condition.
13 caps ('bout $5.00) and 1/2 hour of my time was WELL worth it, it's now my main monitor.
The last 3 were Benq 17 inchers. all are fixed and being donated.
1 to a non-profit organization that I do volunteer sysadmin work for, 1 to a friend, and one to a low-income person in need.

Now I need some more

[bluto]

Re: Gateway FPD2185w- backlight dies after 3 seconds

Curt, did you have any luck replacing the BIT3193G chip?