LG W2234S Repair Help...

[docksteaderluke]

Re: LG W2234S Repair Help...

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

[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

[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?

[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?

[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...

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...

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

[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?

[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...

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?

[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.

[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

[alexanna]

Re: LG W2234S Repair Help...

^ That's kind of what I was thinking, identifying the on/off pin.
And then if needed with switch disconnected take the voltage on that pin low, and see if the monitor stays on.

[PlainBill]

Re: LG W2234S Repair Help...

^ That's kind of what I was thinking, identifying the on/off pin.
And then if needed with switch disconnected take the voltage on that pin low, and see if the monitor stays on.

But even that isn't necessary. LCD monitors usually remember their last state; the power button is just a momentary contact. If the cable to the front panel is disconnected and the monitor still is cycling on and off when you apply power, the front panel switches, pc board, led, etc are not responsible. If it comes on and stays on, or in never comes on, we know the problem is in that portion of the circuit - as you said, probably a stuck switch.

PlainBill

[docksteaderluke]

Re: LG W2234S Repair Help...

Still flashing on and off (LG Logo displayed on the screen for a second or two... then everything turns off) with the front button panel disconnected from the logic board.

Any idea where I can source a replacement logic board? I figure I may as well start looking now but can't seem to find anything via google/ebay...

Are the voltages coming from the inverter pretty much standard across the board? I have an old 17" Samsung that I might hook up to the LG PSU to see if the display keeps turning on or off. That way I'll know if it's the logic board or the backlight.

[PlainBill]

Re: LG W2234S Repair Help...

Still flashing on and off (LG Logo displayed on the screen for a second or two... then everything turns off) with the front button panel disconnected from the logic board.

Any idea where I can source a replacement logic board? I figure I may as well start looking now but can't seem to find anything via google/ebay...

Are the voltages coming from the inverter pretty much standard across the board? I have an old 17" Samsung that I might hook up to the LG PSU to see if the display keeps turning on or off. That way I'll know if it's the logic board or the backlight.

The key is the power light. With one exception, when the backlights go off the power led will stay on. The power LED is switched off and on by the processor on the signal card.

The one exception is if there is a shorted driver in the inverter, and the short overloads the power supply, causing it to shut down.

PlainBill

[docksteaderluke]

Re: LG W2234S Repair Help...

k. So I hooked it up to the 17" LCD panel and the backlight turns on (all white) then off. So it must be the logic board for sure now. I don't think it's a short in the inverter since I swapped it for a new one and it still did the same thing.

So any ideas on where to source a new logic board?

[docksteaderluke]

Re: LG W2234S Repair Help...

Does anyone know if there is any way to test the MX25L1005MC flash IC on the logic board? I can't find a full blown logic board replacement but this IC seems to be an issue with some...

[Rtech]

Re: LG W2234S Repair Help...

I got one from Ebay UK at a huge £35,and that was the last one the Seller had, the others he did have were sold out !!!

[PlainBill]

Re: LG W2234S Repair Help...

Does anyone know if there is any way to test the MX25L1005MC flash IC on the logic board? I can't find a full blown logic board replacement but this IC seems to be an issue with some...

I'm afraid you are SOL on that. Most GPUs bootstrap firmware from an external chip. That chip will usually be identified by marking it with paint. If the contents of the chip gets corrupted, you will get the symptoms you describe. And the MX25L1005MC dies have a blue dot on it.

Someone had a similar problem; he was able to find a copy of the firmware, rig an adapter and reprogram the chip. This could best be described as a non-trivial task. There are a few companies supplying chips preloaded with firmware, however I have only seen this for chips that are in sockets.

I've got a monitor on the shelf with the same problem. What irritates me is the corruption is avoidable. Certain parameters are stored in the firmware chip, rather than in the user eeprom. When the caps go bad a noise spike during a write cycle will corrupt the firmware.

PlainBill