lp2407 aka fpd2485W No Power

[knoxrebel]

Hey guys, new to the forum so please excuse me if i miss something.

I have a gateway lp2407 that shows no signs of power. I get no power lights or picture. I have replaced all the buldging caps on the inverter board, power supply and video board. I still get no lights and no signs of life. The power board does make a buzzing sound for a split second after it is plugged in though. Not sure where to start......

[alexanna]

Re: lp2407 aka fpd2485W No Power

Pictures, of the power supply and logic board using managed attachments please.
Was the no power on, the initial problem?
The flex cable from the front buttons to the logic board is a real PITA are you sure it's not damaged and installed correctly?

[jsog]

Re: lp2407 aka fpd2485W No Power

Pictures posted with the "Attachments" button help a lot (focused, hi-res, and well-lit). Otherwise, check the fuses, and remember that capacitors can fail without bulging. Most people just replace all the electrolytics except the big one. Don't miss the small startup cap, usually 47uf or so.

[knoxrebel]

Re: lp2407 aka fpd2485W No Power

I will post pictures as soon as i get back to work. Yes, the unit not showing any signs of power was the problem. The front panel cable is slightly damaged at the logic/video board side (traces are slightly lifted from the flat cable), but appears to be intact. Would the cause the unit to not power on, i though it would show gateway splash/sounds just from plugging it in.

[alexanna]

Re: lp2407 aka fpd2485W No Power

Would the cause the unit to not power on, i though it would show gateway splash/sounds just from plugging it in.

Most monitors will remember the last state they were in before the power cord is removed. When the power cord is plugged back in if the monitor was on it will turn on. If it was off it will stay off.
I just had one similar to yours, and the front power led was always on any time the power cord was plugged in. If the monitor was off the color of the LED was purple, if it was on the LED was blue.Is that how you remember yours working?
Pictures will help.

[knoxrebel]

Re: lp2407 aka fpd2485W No Power

I dont recall, but i also have a lp2207 and as soon as you plug it in it makes the sound and displays gateway splash.

Also tested smd fuse on inverter board, tests good.

[knoxrebel]

Re: lp2407 aka fpd2485W No Power

Here are the pictures of my boards, I appologize for the glare and bad lighting. The owner is a heavy smoker, this is what the haze is on all components.

All of the lcds that i have worked on would at least power on or have a power light if caps were the only problem. Is this not always the case?

Also i see that many people have used kits from lcd alternatives, are these quality caps?

[PlainBill]

Re: lp2407 aka fpd2485W No Power

Here are the pictures of my boards, I appologize for the glare and bad lighting. The owner is a heavy smoker, this is what the haze is on all components.

All of the lcds that i have worked on would at least power on or have a power light if caps were the only problem. Is this not always the case?

Also i see that many people have used kits from lcd alternatives, are these quality caps?

Oh, yuck. I can only hope the owner's lungs look as bad as the monitor. I considered suggesting gasoline and a match to remove it.

First, on the signal card C501 definitely has a bulge. That cap should be replaced, no matter what other components repair it.

I've marked up the picture of the bottom of the power supply, and have a series of tests for you to make.

First, yellow circles. Set your DMM on the 1000 volt DC range and with the power supply connected to AC, CAREFULLY measure the DC voltage across those points (black probe to the left, red to the right). Report the voltage, it should be greater than 160 volts.

If and only if you read 0 volts across the two yellow circles, unplug the AC power, set the DMM to the lowest ohms range and measure the resistance between the two points circled in beige on the lower left corner. If it reads less than 1 ohm, the fuse is good. If it reads more, the fuse is open. Do not replace it yet, and do not short it out. It blew for a reason and further investigation will be required.

If you got a voltage greater than 160 volts DC on the first test, set your DMM to the 20 volt DC range. On the lower right corner I have marked a point with a black circle. Use that for your black probe. With the power suply connected to AC power, measure the voltage on each of the pins in the area circled in blue. Report those results.

PlainBill

[jsog]

Re: lp2407 aka fpd2485W No Power

This monitor has been repaired before. The blue caps on the inverter are replacements (Lelons!), and three on the power board. One of those three is the wrong size. It has the brown sometimes-conductive glue. Or maybe it was white at first, and is stained like everything else with sticky, poisonous nicotine gunk.

[jsog]

Re: lp2407 aka fpd2485W No Power

And now I reread message #1 and see that you replaced these. Still concerned about the wrong-size one; was it the right capacitance and voltage? Were all the new capacitors low ESR?

[knoxrebel]

Re: lp2407 aka fpd2485W No Power

All the caps that were replaced have been replaced with ones i had lying around from past projects. They were replaced with same capacitance and same or higher voltage.
I replaced the two on the inverter board, three with black marker on power board and 2 out of the 3 bad ones on the video. Ive been doing a lot of research on esr meters and esr for that matter, had no idea that there were so many things that needed to be accounted for when choosing caps. I guess this is one of the reasons they fail so frequently.

[knoxrebel]

Re: lp2407 aka fpd2485W No Power

Plainbill just so im clear, we are testing the voltage on the 150uf 450v cap. Matching polarity.

[PlainBill]

Re: lp2407 aka fpd2485W No Power

Plainbill just so im clear, we are testing the voltage on the 150uf 450v cap. Matching polarity.

Matching polarity is important if you have an analog meter (VOM, TVM, or VTVM).

Any digital meter in built in the last three decades automatically detects and indicates polarity. If you report there is 0 volts across the large cap, the polarity doesn't matter. If you report -325 volts, I understand you couldn't see the + mark, had the leads reversed, and the AC input section is working.

Thanks a lot!!! You just reminded me of another nightmare we could be dealing with. A constant problem when asking someone to measure the resistance between to points is they will report it as '0' (zero). We have to make sure that it actually is a reading of 0 (on the right), rather than O, 'Over range' (on the left). All it would take is several pages of troubleshooting advice to resolve that the leads on an analog meter were reversed to drive me up the wall.

PlainBill

[knoxrebel]

Re: lp2407 aka fpd2485W No Power

Testing across the main cap i get 163-164V. On the connector going to video board going from top to bottom (based on the picture that you reposted with test points) I get.
0
0
0
5.5
0
0
23.3
23.3

[PlainBill]

Re: lp2407 aka fpd2485W No Power

Testing across the main cap i get 163-164V. On the connector going to video board going from top to bottom (based on the picture that you reposted with test points) I get.
0
0
0
5.5
0
0
23.3
23.3

Those voltages indicate the power supply is working. The prospects for fixing a signal card is pretty bleak.

I've circled 5 voltage regulators on the signal card. For each of the regulators list the part number and the voltage on each pin.

PlainBill

[knoxrebel]

Re: lp2407 aka fpd2485W No Power

1 - az1084s
-3.3E1
635j28

2 - A1
AS117L-18
B0637-23


3 - A1
AS117L-33
B0642-85

4- SAME AS 3

5 - AZ11170
-1.8E1
632J57




Sorry, i am not familiar on how to test voltages on the regulators.

[PlainBill]

Re: lp2407 aka fpd2485W No Power

Sorry, i am not familiar on how to test voltages on the regulators.

Not a big deal. Notice that the pins are numbered. Pin 1 is either Gnd (on a fixed voltage part) or the Adj input (for an adjustable part). These are all fixed output voltage parts. The other secret that can save you a few minutes is that pin 2 (not numbered) is electrically connected with pin 4 (the tab).

To test, hook the signal card and power supply together. Set the DMM to the 20V DC range. Plug in the power supply. Hold the black probe on one of the mounting screws. With the red probe check the voltage on pins 3 and 4. The tab is the output, and the output voltage is included in the part number (33=3.3V, 3.3 = 3.3V, etc).

Also, before giving up on this, replace the bad cap.

PlainBill

[knoxrebel]

Re: lp2407 aka fpd2485W No Power

With your explanation and the data sheets for a couple of the line regulators this is a lot easier than i imagined.

At this point i have replaced the last "bad" cap with a 470uf 100v, to replce 470 10v. Im sure that none of the caps i used are low esr as they were spares from parts kits. Would this cause the unit to not function at all or just cause the caps to fail prematurely?

PlainBill I sent you a PM

[PlainBill]

Re: lp2407 aka fpd2485W No Power

With your explanation and the data sheets for a couple of the line regulators this is a lot easier than i imagined.

At this point i have replaced the last "bad" cap with a 470uf 100v, to replce 470 10v. Im sure that none of the caps i used are low esr as they were spares from parts kits. Would this cause the unit to not function at all or just cause the caps to fail prematurely?

PlainBill I sent you a PM

Either. The failed cap was unusual. Permit me to drop into tutor mode.

In very simple terms, there are two types of voltage regulators - linear and switching.

Linear regulators have been around since vacuum tubes. I think of it as a variable resistor - it constantly changes the resistance between the input voltage and the output voltage so the output voltage remains the same, no matter how the input voltage and load current change. It shouldn't take much imagination to realize that a lot of energy can get wasted in a linear regulator. On the other hand, the output requires little filtering - basically just enough to prevent oscillation.

A switching regulator works in a different manner. It switches the current off or on as required to keep the output voltage constant. This occurs at a very high frequency, so relatively small capacitors are required, but they have to absorb high ripple currents, and very low equivalent series resistance - ESR. Using a normal ESR capacitor on the output of a switching regulator will allow more ripple to pass through to the load, and will also cause the capacitor to overheat. If the ripple is high enough, the device won't work.

The capacitor for the output of a linear regulator should not have to endure high ripple. Standard ESR type are suitable. The regulators on this board are linear regulators, so it is unusual to see a cap with a bulging top. The only idea I had was the caps in the power supply allowed enough ripple that the cap on the signal board was cooked.

One concern I have about this is I have a Dell monitor sitting on the shelf that came into my hands dead, with bulging caps in the power supply. After replacing the caps it still did not work. Some testing convinced me the excessive ripple causes corruption of data in the serial eeprom that stores the firmware. I note that your monitor also has a serial eeprom with a telltale dot of paint, so it is susceptible to the same corruption.

PlainBill

[knoxrebel]

Re: lp2407 aka fpd2485W No Power

Here are my test values on the voltage regulators.

------- Pin 3 Pin 4

Chip 1 - 5 ---- 3.3
Chip 2 - 1.3 ---- .5
Chip 3 - 5 ---- 1.3
Chip 4 - 5 ---- 3.3
Chip 5 - 3.3 ---- 1.8