LG W2234S Repair Help...

[PlainBill]

Re: LG W2234S Repair Help...

Alexanna brings up a very good point. What happens if the cable to the front panel is disconnected?

PlainBill

[seanc]

Re: LG W2234S Repair Help...

Now that we've definitely ruled out the PSU, sub in some known good lamps from another monitor and see if the symptoms change.

[alexanna]

Re: LG W2234S Repair Help...

I don't know if the symptoms were the same but we have had problems with the front panel switch,Have you verified voltages toggle low as the buttons are pushed?

[docksteaderluke]

Re: LG W2234S Repair Help...

Symptoms are exactly the same. Both the power LED and the display turn on and off. It only ever gets as far as displaying the LG logo on the screen then shuts off and repeats.

[alexanna]

Re: LG W2234S Repair Help...

Hey guys. It's been a while but I got my hands on a replacement power supply and the problem still remains so it seems like that eliminates the power supply. Where am I hooking up the tail light bulb? to the backlight connectors (CN501-CN504)? Is this still necessary if I know for a fact that the power supply is good?

When you replaced the power supply, have any of the symptoms changed? Is anything different?
Is the power LED still turning off?

[PlainBill]

Re: LG W2234S Repair Help...

So now, if knowing for a fact that this isn't the power board, it seems the only thing left is either the logic board or panel itself. Thoughts?

It's 5:43 AM and I don't really have any coherent thoughts. Well, very few that will help you. It's 99% certainly the signal card is responsible. Both the backlights and the power light are controlled by the signal card. There isn't much that can be done, other than verifying the voltage regulators on the signal card are working properly. Unfortunately, similar problems are reported on other monitors, but I've never seen a solution that didn't involve getting a new signal card.

PlainBill

[docksteaderluke]

Re: LG W2234S Repair Help...

So now, if knowing for a fact that this isn't the power board, it seems the only thing left is either the logic board or panel itself. Thoughts?

[PlainBill]

Re: LG W2234S Repair Help...

Hey guys. It's been a while but I got my hands on a replacement power supply and the problem still remains so it seems like that eliminates the power supply. Where am I hooking up the tail light bulb? to the backlight connectors (CN501-CN504)? Is this still necessary if I know for a fact that the power supply is good?

No, not necessary.

PlainBill

[docksteaderluke]

Re: LG W2234S Repair Help...

Hey guys. It's been a while but I got my hands on a replacement power supply and the problem still remains so it seems like that eliminates the power supply. Where am I hooking up the tail light bulb? to the backlight connectors (CN501-CN504)? Is this still necessary if I know for a fact that the power supply is good?

[alexanna]

Re: LG W2234S Repair Help...

Oh snap! Nice find! That's it for sure.

Here's another approach
First try this identify the on/off pin on the front power switch, see if that voltage goes low when the monitor shuts off.

There are things going on with your monitor that do not make sense.
#1 is the loss of the front PLED
#2 is the monitor is able to briefly turn on the back lamps, but they will not turn on when you provide 3 volts to the on off pin.
If the voltage stay high on the on/ off switch ,I am thinking one problem may be causing the other.
I know you have already done this, but it can't hurt to check it again.
The back light controller has to have the proper power and grounds, if the schematic is correct you should be able to identify them.
The back light controller also has to see an on off signal, it's going to be about 3 volts at the 6 pin connector but it will be much lower at the controller around 1 volt.
I don't think the dim pin is that critical, unless for some reason it was way higher than 1 volt this would be measured at the back light controller.
If all of this is correct the backlights should turn on.
PlainBill suggested loading the power supply; I would suggest using the 1157 tail/turn bulb to ceck the 16 volt rail.I haven't done the math for 16 volts but 12 volts will give roughly between 2 and 2.5 amps,that should be more than enough for the back light circuit.
PlainBill do you have any sugestions?

[nickmatine]

Re: LG W2234S Repair Help...

hi
i have the same problem with same monitor
I'm stuck with lg logo (no power saving mode) all time if i don't have the vga cable from video card
when i plug the cable 2 sec on (with same lg logo) and 2 sec off.
please post here if you found the problem
i suspect the logic board because i changed all caps and checked inverter board
thanks

[docksteaderluke]

Re: LG W2234S Repair Help...

Oh snap! Nice find! That's it for sure.

[alexanna]

Re: LG W2234S Repair Help...

I found this manual in another thread,See if it looks like yours

[docksteaderluke]

Re: LG W2234S Repair Help...

Yes... 3 and 4 are ground pins and the measurements I gave you were with respect to those pins. So... the first measurement was between pins 3/4 and 1/2 which yielded 5V as expected. And you can see that when the backlight is on the load is slightly higher and the voltage drops a wee bit (4.98V when the backlight is on as opposed to 5.09V when the backlight is off) which is expected. That much seems right.

[alexanna]

Re: LG W2234S Repair Help...

Here are the measurements I get:

Pin (Label) - Backlight ON, Backlight Off

1/2 (Power) - 4.98V, 5.09V
5 (On/Off) - ~2.9V, ~0.4V
6 (Brightness) - <0.2V, 3.3V

Something strange is going on.
As always I have some more questions.
Are pins 3 and 4 ground pins?
You could verify this by touching the negative lead of the DMM to pins 3 and 4 and touching the positive lead to pin 1 if they really grounds you should see 5 volts.
Check these when you see the lights on and again when off.

[docksteaderluke]

Re: LG W2234S Repair Help...

Here are the measurements I get:

Pin (Label) - Backlight ON, Backlight Off

1/2 (Power) - 4.98V, 5.09V
5 (On/Off) - ~2.9V, ~0.4V
6 (Brightness) - <0.2V, 3.3V

[alexanna]

Re: LG W2234S Repair Help...

Hey guys. My replacement caps finally arrived! I swapped out all of the electrolytic caps and tried hooking the monitor up again and it does the same thing! Looks like it wasn't any of those caps after all. Could it be the EEPROM chip on the logic board? I had read in another thread that it can sometimes get corrupted.

Help!

I wonder if you would satisfy my curiosity, on some things.
Could you verify the voltages you see on the 6 pin connector from the power supply to the logic board?
Have the voltmeter hooked up and then power the monitor on, and measure when the backlights or on and again when they turn off.

[docksteaderluke]

Re: LG W2234S Repair Help...

Hey guys. My replacement caps finally arrived! I swapped out all of the electrolytic caps and tried hooking the monitor up again and it does the same thing! Looks like it wasn't any of those caps after all. Could it be the EEPROM chip on the logic board? I had read in another thread that it can sometimes get corrupted.

Help!

[docksteaderluke]

Re: LG W2234S Repair Help...

Varying the brightness voltage from ~0V to ~5V does not seem to have had any effect. Waiting on the caps to ship. When they arrive I'll swap 'em out and get back to you. So, does it seem like the consensus is that it's the power supply. I can probably order a new one for $35ish (ebay!) if the recap doesn't work.

[PlainBill]

Re: LG W2234S Repair Help...

I'm sourcing some caps right now. I'll give some of your other suggestions a try when I get home from work.

When rigging a resistance load (to the inverter outputs I'm assuming) what sort of resistance is needed?

I was referring to the power supply outputs. A 2 - 3 amp load in the 5V supply and optionally 1 amp on the 12V would be my suggestion.

PlainBill