LP2407 FPD2485W 15 seconds to black

[TheMav]

Hello, my name is Brad and I am new to this forum. I recently bought a Gateway LP2407 at a thrift store and I could use some help fixing it. When I hook up the monitor, it powers on, displays the gateway symbol and does it's little jingle. The screen doesn't display anything for about 15 seconds, then it says "no signal" and then the monitor shuts off. I've searched through this forum but I have not been able to find a similar problem yet. Does anyone know what this kind of start-up indicates?
I know pictures are important, so I will be uploading them in a few hours.
Thanks.
Brad

[budm]

Re: LP2407 FPD2485W 15 seconds to black

It is not detecting the video signal from the PC so it goes into standby mode.

[TheMav]

Re: LP2407 FPD2485W 15 seconds to black

So I've been doing the same things as the guy in this thread which means I've been following the steps given in posts #8 and #15 by PlainBill in this thread.
I measured the voltage across the large cap and it was 166 (in spec). I then measured the voltages on the outputs to the inverter(?) board, as indicated in post #8 I mentioned. From top to bottom the voltages were as follows:
0
0
0
5.4
0
0
22.9
22.9
Those appeared to be in spec.

As instructed in post #15, I then looked at and measured the voltages on the 5 voltage regulators. In my picture they are numbered. Here are my part numbers and measured voltages:
1) AS1117L-18 - Pin 3: 4.04v -- Pin 4: 1.79v
2) AS1117L-33 - Pin 3: 5.1v -- Pin 4: 1.31v
3) AS1117R-18 - Pin 3: 3.28v -- Pin 4: 1.78v
4) AZ1084S-3.3EI - Pin 3: 5.1v -- Pin 4: 3.3v
5) AS1117L-33 - Pin 3: 5.08v -- Pin 4: 4.05v

Is pin 3 on each of these regulators the rail voltage? If so, it looks like the rail voltage on #1 is high since from the other forum it appears that it should be about 3.3v. Also, it looks like regulators #2 and #5 are bad, since #2 is under voltage and #5 is over voltage. I will try to replace those, but what about the high voltage on pin 3 on regulator #1? Should I replace that regulator, or is there a different problem?
Do any of these problems explain why the monitor is not detecting the video signal?
Thanks for any help.

[budm]

Re: LP2407 FPD2485W 15 seconds to black

Detecting of the Video signal is done by the main logic board, you can have non-function inverter board, it still should detect the video signal.
Number 2 (should have 3.3V output) and Number 5 (should have 3.3V output) are bad, that can be due to and regulator, overloading, bad filter caps.
There are 3 legs for the regulator, Input pin output pin, Ground pin.

1) AS1117L-18 - Pin 3: 4.04v -- Pin 4: 1.79v, 1.8V regulator
2) AS1117L-33 - Pin 3: 5.1v -- Pin 4: 1.31v, 3.3V regulator
3) AS1117R-18 - Pin 3: 3.28v -- Pin 4: 1.78v, 1.8V regulator
4) AZ1084S-3.3EI - Pin 3: 5.1v -- Pin 4: 3.3v, 3.3V regulator
5) AS1117L-33 - Pin 3: 5.08v -- Pin 4: 4.05v, 3.3V regulator

[TheMav]

Re: LP2407 FPD2485W 15 seconds to black

So the other thread explained that pin 1 is the ground pin and pin 4 is the output pin, which would make pin 3 the input pin. So on regulator #1, is it okay that the input (pin 3) is 4.04v?
Should I just replace the regulators? Or do I need to investigate more?
None of my caps looked bulged at all on any of the boards. Can I assume they are good, or is there a way that I should check them?

[budm]

Re: LP2407 FPD2485W 15 seconds to black

XX1117 LDO Regulator, when you look at it with the big tab up, left pin is the pin 1 (Ground pin for fixed regulator), middle pin is tied to the big tab is an Output pin, right pin in the Input pin.
"So on regulator #1, is it okay that the input (pin 3) is 4.04v?" The output is OK but it is being fed with 4.04V which if the power supply is 5V then your input is low. You will need to trace out where the 4.04V is coming from, I would expect it to be fed by 5V so check the out put of the 5V power supply section. Cap should be tested with ESR meter beside the capacitance meter.

[TheMav]

Re: LP2407 FPD2485W 15 seconds to black

So I was measuring the voltages that are output from the power board to the signal board and after unplugging the power board, I accidentally shorted and discharged the 450 V capacitor (POP! DMM electrode brushed across the cap nodes). I'm inclined to think that this didn't damage anything, it just discharged, but... Could this damage things?

[budm]

Re: LP2407 FPD2485W 15 seconds to black

It may damage the bridge rectifier, the main AC fuse.

[TheMav]

Re: LP2407 FPD2485W 15 seconds to black

Just wanted to update the status of my repairs. I replaced the two faulty voltage regulators and success! The monitor is working again.
It feels good to have only spent $40 plus $1 in parts on a 24" monitor!
To those with a Gateway LP2407, check your regulator voltages!
Thanks for the help,budm!