Gateway 900G frustration

[stroogly]

Hi All,

I have about 10 Gateway 900G 19" LCD monitors with the same problem.

They make a slow ticking and the 5V bounces in time with the ticking.

If I had a camera here I would take a pic of the guts, but I don't have one so I'll give a description.

It is a 4 lamp 19" LCD with the power supply (100-240AC in) and inverter on one board. It has your basic 12V 5V switching power supply with 12V going to the inverter section.

Here's what I know so far:

It is not caps. I replaced all the electrolytic caps even though they look fine. Same problem.

It's not the inverter section. I remove the jumpers to the inverter, same problem.

It's not any of the power semis (switching transistor and rectifers ok, rectifies AC in OK)

It's not the logic board. (Swap know good power supply and it works fine)

The biggest clue I have so far (least I hope it's a clue) is that the 5v bounces from 0 to 5 in time with the ticking, but the 12V barely bounces at all! I have double checked the rectifier and the caps on the 5V.

The 5V does this even when the logic board is disconnected.

Any ideas?

Much thanks-

Michael

[Scenic]

Re: Gateway 900G frustration

[...] but the 12V barely bounces at all!

mhh... short on 12V somewhere?!

just a guess..

[Krankshaft]

Re: Gateway 900G frustration

A protection circuit is kicking in so there must be a short on the secondary side somewhere.

Pictures are pretty essential here to tell you where to start hunting.

[EGuevarae]

Re: Gateway 900G frustration

It is not caps. I replaced all the electrolytic caps even though they look fine. Same problem.

Replaced with what brand/series?

I repaired one of these changing a 10uf 25v for a 25uf 50v (Nichicon 105c) but I can't find my notes right now to see the original brand/series, and where it was located. The click was present and the bounce was between 1.78 and 3.98. After that, the V was stable at 5.03v

[Toasty]

Re: Gateway 900G frustration

>>(Swap know good power supply and it works fine)<<
If you take the good supply (lucky you!) and put it in one unit and start checking and comparing voltages between the dead units, you should be able to narrow it down.

Failing that, take the good supply and a bad one and start a resistance check from main points to others. Sometimes this can really nail the dead part.

Toast

[stroogly]

Re: Gateway 900G frustration

Interesting information!

eguevarae: I did not fiddle with the little electrolytic caps, but I know what your saying! I don't have the board in front of me, but I believe there is only *1* electrolytic that is that small. I'll try your suggestion tomorrow.

toasty: I tried comparing voltages between the good and bad ones, but all the interesting areas of the circuit on the bad one are bouncing up and down with the ticking like a bunch of drunk kids in a mosh pit! I'll get really meticulous tomorrow with comparing the circuits without power. I compared the transformers, diodes, transistors and opto isolator and they all look the same.

Thanks! You guys are great!

-Michael

[Toasty]

Re: Gateway 900G frustration

Just to clarify. Check the resistances with units disconnected from everything.

Description is okay, but we'd like to SEE the patient. Cellphone cam??

[EGuevarae]

Re: Gateway 900G frustration

Description is okay, but we'd like to SEE the patient.

Badcaps.MED?

[stroogly]

Re: Gateway 900G frustration

All hail eguevarae! And thanks to everyone else.

There is a 47uf/25v cap next to the switching transistor; I didn't trace it out but it looks like it is part of the network that gets feedback from the optoisolator on the primary side.

Anyway, replacing it with a 100uf/25v make the circuit magically come to life. The kicker is the one I pulled measures 40uf and holds a charge. That's damn close to what it should be, but apparently not good enough.

I guess the lesson is you need to be suspicious of ALL electrolytics regardless of how small and insignificant they seem to be.

I'll fix all of them and leave a general description of what I find out.

-Michael

PS: Here's a pic of the patient with the offender in a red circle. The filter caps on the secondary side have all been replaced with bigger better caps on this one.

[Toasty]

Re: Gateway 900G frustration

Thanks for the pic! Good Job!

Sounds like the cap dried out or was weak to begin with. What brand & series was it? (for the record) If you have others of the same on there, might as well check/replace them all.

Most aluminum electrolytics read OVER their capacitance rating. There are exceptions, but in this application, I'd expect that cap to read 55-60uF.

[stroogly]

Re: Gateway 900G frustration

All the electro caps in all the monitors were Samxon GF. I wanted to make sure GF was the series, so I googled "Samxon GF". Can you guess what the first 2 hits were?

Cheers-

-Michael

[EGuevarae]

Re: Gateway 900G frustration

All hail eguevarae! And thanks to everyone else.

There is a 47uf/25v cap next to the switching transistor; I didn't trace it out but it looks like it is part of the network that gets feedback from the optoisolator on the primary side.

Anyway, replacing it with a 100uf/25v make the circuit magically come to life. The kicker is the one I pulled measures 40uf and holds a charge. That's damn close to what it should be, but apparently not good enough.

I guess the lesson is you need to be suspicious of ALL electrolytics regardless of how small and insignificant they seem to be.

I'll fix all of them and leave a general description of what I find out.

-Michael

PS: Here's a pic of the patient with the offender in a red circle. The filter caps on the secondary side have all been replaced with bigger better caps on this one.

Board is a bit different, and so the cap rating, but the principle is the same. I started to replace the bad caps from top to bottom. This was the last I replaced, and just to make sure it wasn't the culprit : it was.
I mean, I replaced the ones at the top right of your pic because they bulged (PSU still managed to power On, but with the "relay" click...) and I said "that's it". But the noise and bouncing was still there. Then I replaced that little guy and voila! Stable 5V.
I didn't had my camera those days, so no pics. And I didn't make a note of the original brand/series for that particular one, but it is the same as in the pic, so if you can provide the data, it would help others in the future.

Good to hear I was of any help.

And welcome to Badcaps.Net

[PlainBill]

Re: Gateway 900G frustration

All hail eguevarae! And thanks to everyone else.

There is a 47uf/25v cap next to the switching transistor; I didn't trace it out but it looks like it is part of the network that gets feedback from the optoisolator on the primary side.

Anyway, replacing it with a 100uf/25v make the circuit magically come to life. The kicker is the one I pulled measures 40uf and holds a charge. That's damn close to what it should be, but apparently not good enough.

I guess the lesson is you need to be suspicious of ALL electrolytics regardless of how small and insignificant they seem to be.

I'll fix all of them and leave a general description of what I find out.

-Michael

PS: Here's a pic of the patient with the offender in a red circle. The filter caps on the secondary side have all been replaced with bigger better caps on this one.

Michael,

Thanks for the information. I had a dead Gateway FPD1760 (700G) with the same symptoms. (Looks like the identical power supply). A couple of the larger caps looked a little dodgy so I replaced all of the 470uf and 220uf ones, but didn't bother with that one (it's never the little ones that fail, right?) Thanks to your information my Grandson now will have a 17" LCD monitor.

PlainBill

[EGuevarae]

Re: Gateway 900G frustration

Michael,

Thanks for the information. I had a dead Gateway FPD1760 (700G) with the same symptoms. (Looks like the identical power supply). A couple of the larger caps looked a little dodgy so I replaced all of the 470uf and 220uf ones, but didn't bother with that one (it's never the little ones that fail, right?) Thanks to your information my Grandson now will have a 17" LCD monitor.

PlainBill

That's what I told you : the little one was the guilty among all his bigger brothers. And the monitor I referenced was that very same : a FPD1760(700G). Now they are three (counting mine) failing with that symptoms that are failing due to this little guy. Just take a note of that.

[Wizard]

Re: Gateway 900G frustration

Hehe, little one do pack serious sting where you least expect. That why I check all capacitors of any sizes in a power supply and IP boards.

Cheers, Wizard

[arpcentralone]

Re: Gateway 900G frustration

Hi, I have an IC Power 900G with the same type of power supply. It clicked like above, and I replaced all caps EXCEPT the culprit.. after reading this, I recapped it too, and it worked for that problem. Now, when the monitor comes on, it stays on for 1 second, then the screen goes blank, but the green light stays on. I just replaced that cap with a 470uf 25V cap that I used to replace the others, the voltage was the same as the culprit, however, the uf was lower. Do you think this may account for the other problem i'm having?

Thanks!

[PlainBill]

Re: Gateway 900G frustration

Hi, I have an IC Power 900G with the same type of power supply. It clicked like above, and I replaced all caps EXCEPT the culprit.. after reading this, I recapped it too, and it worked for that problem. Now, when the monitor comes on, it stays on for 1 second, then the screen goes blank, but the green light stays on. I just replaced that cap with a 470uf 25V cap that I used to replace the others, the voltage was the same as the culprit, however, the uf was lower. Do you think this may account for the other problem i'm having?

Thanks!

Unlikely. Most likely you have a problem with the inverter or CCFLs. The next test gets a little more complicated. After the display blanks (but the power led stays green) hit the power button to turn the monitor off, then again to turn it on. If the screen flashes on again for a second, then goes blank again you have confirmed the problem is in the backlight circuit.

A little background: The backlight circuit is pretty much self contained. The inverter gets power from the power supply (obviously), and two control signals from the logic board - On / Off and Brightness. It doesn't feed any information back to the logic board. When the inverter gets the 'On signal it turns on. Then it monitors the current draw of the CCFLs. If they are drawing too much or too little current the inverter shuts down again.

The trick is to figure out which CCFL is responsible, or if it's the inverter itself.

PlainBill

[arpcentralone]

Re: Gateway 900G frustration

Hi, thanks for the reply. You are more than likely correct. I am going to post some pics in a while of the board which is ALMOST just like the one above. Could you help me to point out the inverter?

Thanks!

[arpcentralone]

Re: Gateway 900G frustration

Here are some photos.. the one titles trans.jpg is a pic of a shunt regulator. KIA431A. I removed it, tested it, and put it back on (backwards) before I actually fixed the "no power, bad cap" problem, so this may have something to do with it. I desoldered it and put it back in right, and now I have the problem of a blank screen after 1 second.

[PlainBill]

Re: Gateway 900G frustration

Here are some photos.. the one titles trans.jpg is a pic of a shunt regulator. KIA431A. I removed it, tested it, and put it back on (backwards) before I actually fixed the "no power, bad cap" problem, so this may have something to do with it. I desoldered it and put it back in right, and now I have the problem of a blank screen after 1 second.

First point: The shunt regulator is part of the regulator circuit. Check the output voltages of the power supply. The connector is labeled. If you have 5 volts at the 5V pin and 12 volts at the 12V pin (if there is one), the shunt regulator is not damaged.

Second point. All of the 300 series components (i.e. C301, JP311, and R301, R322, etc on the back) are part of the inverter primary. 100 series components are part of the line side of the main power supply; 200 series are part of the secondary side; and 400 series are part of the output (high voltage) side of the inverter. A good thing to remember is that 100 series components can carry enough voltage and current to kill you, 200 and 300 are 'safe', while 400 series will certainly give you a jolt but probably won't kill you.

Most of the circuitry for the inverter is on the back side of the board. Pictures of that might help. I'm not sure why, but there seems to be TWO sets of transformers. And even more strange, the two small ones have numbers indicating they are part of the line voltage.

PlainBill