Power supply troubleshooting on LG W3000h-bn

[zorgkang]

Hi! My LG W3000h-bn switched to standby while working, and has been stuck in standby mode since, even after hard restarts. I've confirmed the computer, cables and mains are fine. The power button works but goes straight to amber standby light, the display never comes on.

I've opened up the unit and started testing the power supply. Visual inspection reveals nothing (caps look fine). With PS disconnected from all other boards, I only get 5V on the standby 5V and "ADC", a few mV on 6V and 12V outputs, and 0V on everything else. I noted that the standby 5V seems to oscillate, but only between 5.0 and 5.2V. With the board that has the video input connectors on it (what's that called?) plugged in, and the power/menu buttons plugged into that board so I could turn it on, I get:
ADC and ST5V: 5.07V (stable now)
6V: 6.6V, but seems to slowly drop over time, last measure a few minutes later was at 6.2V.
12V: 12.07V
19V: 17.8V, also seems to drop over time.
24V: 0V
3.4V: 0V
On/Off: 84mV
I-C: 84mV
Dim: 3.27V
Err: 0
I-B: 0
Bri: 0

Not sure what Bri, I-B, I-C, ADC are. I'm not too sure what to conclude with this. The monitor still stays in standby mode, so I'm guessing the 0's could be "normal". Is there a way to force it to turn on to test the voltages? I didn't find any "service manual" or such for this monitor.

Pics attached. Any help greatly appreciated!

[zorgkang]

Re: Power supply troubleshooting on LG W3000h-bn

I found my PS was the same as in this post: https://www.badcaps.net/forum/showthread.php?t=19546
And they said to pull up the On/Off through a 1k resistor from the ST5V, which I did. Here are the voltages:
ADC and ST5V: 5.0V
On/Off: 2.9V
6V: 8V
12V: 12.5V
19V: 20.0V
24V: 24.4V
3.4 On: 0
3.4V: 0

So... looks pretty good, but I would have preferred something on the 3.4V. I presume the 3.4 On pin signal comes back from the other board, I guess it could be what I'd need to pull up to turn on the 3.4V? Also that 6V seems pretty high at 8V, but I wouldn't guess that's my problem. Any suggestions of what to test next?

[budm]

Re: Power supply troubleshooting on LG W3000h-bn

On/Off: 2.9V: This is the receiving pin that receives the ON (BL-ON. INVR-ON) signal from the main board to turn on the Backlights inverter circuit.
3.4V_ON also looks to be the receiving pin that receives the ON signal from the main board to turn on the switched 3.4V supply.
What is the power supply board P/N? I cannot read it from the pictures.

[zorgkang]

Re: Power supply troubleshooting on LG W3000h-bn

Ah good point. There are a couple:
P/N: EAX31845201/13 rev 1.2
HE is marked (vs YY) as is 32" EAY3305850 (vs 37" EAY3306450)
Model: LGLP3237HEP

[zorgkang]

Re: Power supply troubleshooting on LG W3000h-bn

Just looked at your basic troubleshooting guide, very informative, thanks!
It would seem my problem is with the logic board, would you agree? I've found this written on the logic board:
W3000H
Chassis: LM82A
EAX39284802(0)
071031 J.K LIM

Also some stickers: 1: 82EBR040-8633, GB82FZ00JC; 2: 83EBT000-3068, DG 811.000.

Sadly, the PS was common to a few models and available to buy online, but a quick search yielded nothing for this board.

[zorgkang]

Re: Power supply troubleshooting on LG W3000h-bn

Ok, I'm running out of options, but if there's a way to fix this, I would really appreciate the help. I'm still going with the assumption that the problem is the main board. After some back and forth on the phone with LG and the local LG repair shop, LG gave me the part number (which apparently is not the one written on the part): EBR41359301.
I was very excited to find a few online stores sold it (without any description though so couldn't confirm it was the right part). But after ordering it and waiting 3 weeks, they finally told me it was discontinued. Called LG again and they confirmed. So now it looks like my only option would be to fix the main board.

I don't really know where to start, but I'm thinking if there's a way to bypass the part that controls sleep mode, then maybe it would work again. Any suggestions of what to look for or try? A new monitor will cost me a grand, so I'm willing to put some effort/time into this!

[momaka]

Re: Power supply troubleshooting on LG W3000h-bn

Post some pictures of the video board here.

[zorgkang]

Re: Power supply troubleshooting on LG W3000h-bn

Indeed. Here they are.

[momaka]

Re: Power supply troubleshooting on LG W3000h-bn

I see several small caps and at least one linear regulator there.

Let's start with IC301. It's that black linear regulator in a SOT-223 package. I did some searching on the numbers written on it (EH13A), and its actual part number is AZ1117H-1.8TRE1, in case anyone needs to find a datasheet.
It's a 1.8V linear regulator, so measure the voltage on pins 2 and 3. Let me know what you get.

Also, there are two more ICs that might be linear regulators. One is in a SOT23-6 (SOT363) package and is next to a small brown electrolytic capacitor C337. The other one is in a TO-92 package. Let me know if you can read any part numbers off of them.

Finally, check diode D316 with your multimeter on diode test mode (remove power to the monitor first, of course).

There is some chance that a few of those small electrolytic caps may be bad too, considering that I see two on there that are rated for 85C only.

[zorgkang]

Re: Power supply troubleshooting on LG W3000h-bn

Thanks momaka, finally have some time to work on this again.

I plugged just the main board through my DVI cable in the video card and I can confirm that the computer properly recognizes it and reads the EDID. The DVI pins for Hot Plug Detect and 5V standby from PC also seem good with ~5V on them when plugged.

The diode D316: IN734 B3 4 "Zener voltage regulator diode"; forward biased: 0.16V drop, reverse biased: OL. (seems ok?)

I didn't remove any components yet and I only have a basic multimeter, but I found most caps seemed ok when testing in resistance mode (starts low and gradually goes up to OL), except 2 that stay low, but that could be the circuit: C345 ~.9k, C326 ~3.9k. (I guess it's worth taking them out to test again?)

Then I measured voltages when powered by the supply board and using the power button to turn it on (it shows the standby amber light):

• IC301 is actually LD1117A-33H-08-TR30 low dropout positive voltage regulator. It checks out with 5V at input, 3.3V output.

• IC100 (the TO-92) is K1A7042AP voltage detector. I didn't exactly understand it's operation, but I measure 5V at input, 0.72V at output. (No change if I turn the monitor off, or unplug the DVI cable.) I expected the output to be close to input, but as I said not sure how it actually works. To check further.

• IC303 (the SOT23-6 you asked about) has markings: IANAN (or 1ANAN). Couldn't find what that is. Four pins are at 5V, two at 0.12V (so no ground).

• I also checked the power to the 2 EEPROM chips, Vcc = 5V on the one near the MCU and 4.55V on the one near the DVI plug. Seems ok.

Finally, the connections to the power supply board have different pin names on the main board, so here's again what I get. Basically, everything looks ok except the first two "on/off" that never turn on.
ON/OFF = MOD-CTL ("mod"?): 0.08V
I-C = INVONOFF-CTL (inverter control): 0.08V
ADC = AC-DET (mains detection?): 5V
3.4_ON = USB-ONOFF (USB power control?): 0V probably because I haven't plugged USB
3.4V = USB3.3V: 0V makes sense with above, and if it's only for USB, not important
ST5V = 5V (5V for standby?): 5V
DIM = BRT-CTL (dimming/brightness control): 3.27V

A few more from the plug that goes to the TCON board (but not connected):
PWR (power control): 0.08V guessing linked to MOD-CTL above
5VHPD (hot plug detect): 5V
SCL (serial clock): 5V
SDA (serial data): 5V
AGP (?): 0.07V
DCR (dynamic contrast function?): 0V
ABR (automatic brightness function?): 0V

After these tests, I wanted to try and plug everything else and check voltages again (TCON to main board, backlight inverter board to power), but cables were too short and I ended up shorting and blowing the power supply fuse... Anyway, once I replace the fuse and check the supply, any tips on what to do next? Am I correct that it's the main board that's supposed to send the "on" signal to the TCON (PWR pin) and PSU (ON/OFF and I-C pins), and in turn the PSU sends it to the inverter board (I-C pin)? I'm just wondering if these pins are off because some connections were missing.

[momaka]

Re: Power supply troubleshooting on LG W3000h-bn

I plugged just the main board through my DVI cable in the video card and I can confirm that the computer properly recognizes it and reads the EDID. The DVI pins for Hot Plug Detect and 5V standby from PC also seem good with ~5V on them when plugged.

Good to know. So the logic board may actually be working properly.

The diode D316: IN734 B3 4 "Zener voltage regulator diode"; forward biased: 0.16V drop, reverse biased: OL. (seems ok?)

Looks more like a schottky diode based on where it is positioned on the board and the readings you are getting. I don't think 1N734 is the right part number, because that point to a Zener diode with a Zener voltage of 58V (which doesn't really make sense in this circuit)
Either way, since it reads OL in reverse bias, it is *likely* okay (sometimes diodes can become leaky in reverse bias, but it is a rare case)

... but I found most caps seemed ok when testing in resistance mode (starts low and gradually goes up to OL)

I used to do this test as well, back when I started learning to repair electronics. But now I find it rather useless - at least for testing if caps are good or not. You can only use it to check if a capacitor is short-circuited, which almost never happens.

Then I measured voltages when powered by the supply board and using the power button to turn it on (it shows the standby amber light):

• IC301 is actually LD1117A-33H-08-TR30 low dropout positive voltage regulator. It checks out with 5V at input, 3.3V output.

Looks good.

• IC100 (the TO-92) is K1A7042AP voltage detector. I didn't exactly understand it's operation, but I measure 5V at input, 0.72V at output. (No change if I turn the monitor off, or unplug the DVI cable.) I expected the output to be close to input, but as I said not sure how it actually works. To check further.

• IC303 (the SOT23-6 you asked about) has markings: IANAN (or 1ANAN). Couldn't find what that is. Four pins are at 5V, two at 0.12V (so no ground).

Hmm... I can't find any further info on these either.

3.4_ON = USB-ONOFF (USB power control?): 0V probably because I haven't plugged USB
3.4V = USB3.3V: 0V makes sense with above, and if it's only for USB, not important

I always thought USB devices needed 5V.
Might be worthwhile to pull "3.4_ON" high (I am guessing either 3.3V or 5V) to see if 3.4V rail comes up. Better yet, try plugging in a flash drive to confirm your theory above.

I simply don't understand why this PSU has a 3.4V output. Seems too complex for its own good .

After these tests, I wanted to try and plug everything else and check voltages again (TCON to main board, backlight inverter board to power), but cables were too short and I ended up shorting and blowing the power supply fuse... Anyway, once I replace the fuse and check the supply, any tips on what to do next?

Well, let us know when you get it running. If the fuse has blown, chances are there are other parts blown as well. Only if you were lucky and the AC input shorted (but nothing else), then a new fuse might fix it.
Let us know, though.

Am I correct that it's the main board that's supposed to send the "on" signal to the TCON (PWR pin) and PSU (ON/OFF and I-C pins), and in turn the PSU sends it to the inverter board (I-C pin)? I'm just wondering if these pins are off because some connections were missing.

Yes, that is likely how it it. However, before the main board can send these signals, it checks if AC DET is high (which it is).

I also see an "ERR" (error?) pin on the PSU board. Makes me wonder what that does. Looks like it's going to the inverter. But even if that is the case, the inverter only has a 24V input, so when the main PS is down, the inverter won't be sending out any error signals.

So pretty much the only voltage I am worried about is 3.4V and why it's not there.

[stj]

Re: Power supply troubleshooting on LG W3000h-bn

http://elcodis.com/parts/6060058/UPA602T.html#datasheet

could be IAN

[zorgkang]

Re: Power supply troubleshooting on LG W3000h-bn

Wasn't able to get the fuse locally, so might take a few weeks to receive it. I'll definitely let you know how it turns out, and if it works I'll check some more the 3.4V as you suggested.

[cyjun1990]

Re: Power supply troubleshooting on LG W3000h-bn

any update zorg?

[dbox123]

Re: Power supply troubleshooting on LG W3000h-bn

Having same issue with same monitor. Windows recognizes the monitor, but it stays in standby. I assume it's the EBR41359301 board as well. Wondering if you ever got anywhere with this? I can't find any of the boards online so looks like it's probably a lost cause. Too bad. I loved that monitor.