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**Dogcatdog** · 10-19-2015, 04:40 AM

Re: Acer G235H Abid (dead) no indicator LED

anyone please ???

**Dogcatdog** · 11-02-2015, 08:40 PM

Re: Acer G235H Abid (dead) no indicator LED

i might be doing something completely wrong, with the above information

**momaka** · 11-02-2015, 11:35 PM

Re: Acer G235H Abid (dead) no indicator LED

Good work troubleshooting so far!

Seems like you are getting a proper voltage (5V from PSU board) to the main/logic board. That said, there are two linear regulators on your logic board: one is in a TO-263 package (big component, top-left corner) and the other in TO-252 (top-right corner). (Google-image search those package numbers if you don't know what I am referring to.) I'm using this picture as a reference right now:
https://www.badcaps.net/forum/attach...0&d=1444640175
Can you post their part numbers? Or, better yet, take some voltage measurements of their tabs and their right-most pins with respect to ground. You can use the monitor's chassis as ground. One of them should have 5V on the input and 3.3V on the output (probably the TO-263 component). The other might have 3.3V or 5V as the input and 2.5V or 1.8V as the output. But let me know what voltages you get so we can see if they are any good.

Also, just because you are getting an output voltage from the PSU and the caps measure fine in capacitance doesn't mean that they are still good. A capacitor can have a proper capacitance but develop high ESR. What that translates to is that the capacitor will not be able to function properly in the circuit. Therefore, I would highly recommend that you at least change all of the electrolytic capacitors on the 5V rail of the PSU as well as all of the small electrolytic caps on the logic board (the ones near the regulators).

**Dogcatdog** · 11-03-2015, 10:14 PM

Re: Acer G235H Abid (dead) no indicator LED

Hi momaka,

thank you very much for the help, i very much appreciate your time, sorry for the late reply i was sick, here is the information that you have requested.

left one is [UTC UZ1084L 3301 NEC4] i guess its the 3.3V http://pdf1.alldatasheet.com/datashe...X-TA3-A-T.html gives me: left pin 0.0V, middle pin 3.24V, right pin 5.18V

the right one is [UTC LD1117AL 12A01wgpf] i guess its the 1.2V one http://pdf1.alldatasheet.com/datashe...2-AA3-A-R.html, gives me: left pin 0.0V, middle pin 1.2V, right pin 2.54V

i will replace all the capacitors this week and try it again, but maybe the above information helps to diagnose further the problem.
btw. how do i identify the 5V rail?

thank you very much in advance

**momaka** · 11-04-2015, 10:12 PM

Re: Acer G235H Abid (dead) no indicator LED

Originally posted by Dogcatdog View Post

here is the information that you have requested.

left one is [UTC UZ1084L 3301 NEC4] i guess its the 3.3V http://pdf1.alldatasheet.com/datashe...X-TA3-A-T.html gives me: left pin 0.0V, middle pin 3.24V, right pin 5.18V

the right one is [UTC LD1117AL 12A01wgpf] i guess its the 1.2V one http://pdf1.alldatasheet.com/datashe...2-AA3-A-R.html, gives me: left pin 0.0V, middle pin 1.2V, right pin 2.54V

Looks good. The regulators seem to be working fine.

The second one (the 1117AL) seems to be getting only about 2.5V on the input. That means there must be a 2.5V regulator somewhere as well.

Either way, let us know what happens after the recap.

Originally posted by Dogcatdog View Post

btw. how do i identify the 5V rail?

If you look at this picture you posted:
https://www.badcaps.net/forum/attach...3&d=1444640175
You can see that the pins for the wires going between the power supply and logic boards are labeled.

BRI -> LCD brightness control (the logic board sends a voltage between 0-3.3V to the inverter IC on the power supply board to set the brightness)

ON/OFF -> backlight control (the logic board sends a signal to the inverter IC on the power supply board to turn ON/OFF the backlights)

5V -> this is the 5V rail I am talking about. Simply follow the traces on the power supply board to see which electrolytic caps are connected to it. Once you do, change those caps.

GND -> obviously ground

**Dogcatdog** · 11-05-2015, 04:32 AM

Re: Acer G235H Abid (dead) no indicator LED

thank you very much for the help and info, i replaced the caps today and the result is exactly the same, unchanged. there is no difference at all i checked also all the voltages they are also the same as before.
please let me know what the next step would be, what else i can test.
attached img. of replaced caps
i dont have any to replace the other 5 caps, i will get them this weekend, then i replaced them all, except the fat primary one which works otherwise i would have no power at all i guess.

thank you in advance

Attached Files

**momaka** · 11-05-2015, 06:27 PM

Re: Acer G235H Abid (dead) no indicator LED

Originally posted by Dogcatdog View Post

i replaced the caps today and the result is exactly the same, unchanged. there is no difference at all i checked also all the voltages they are also the same as before.

Did you change the small caps on the logic board as well. By that, I mean this one:
https://www.badcaps.net/forum/attach...0&d=1444640175

Also, do any of the chips or regulators on the logic board run hot? Another thing to check would be the HDMI port - make sure the pins inside it are not shorted.

Originally posted by Dogcatdog View Post

i dont have any to replace the other 5 caps, i will get them this weekend, then i replaced them all, except the fat primary one which works otherwise i would have no power at all i guess.

Yes, you don't need to replace the big primary cap. They almost never fail. The other 5 caps on the PSU board are most likely only for the inverter. I guess you can try replacing them, but I doubt that would change the symptoms.

Also, can you post pictures of the front panel board? (i.e. the board with the ON/OFF button) I am guessing it only has switches on there an no resistors.

**Dogcatdog** · 11-06-2015, 07:46 AM

Re: Acer G235H Abid (dead) no indicator LED

Today i replaced also all the caps on the main board,symptoms are still the same. unchanged, i checked if anything gets worm or hot, but there is nothing, not even warm, so no change in temperature, i also checked the HDMI port, and checked also the DVI and VGA if there is anywhere a short, but there was no short.

here the pictured of the on/off panel board, i checked also the resistors and also wrote in the pics the markings and DMM measurements

thank you very much

Attached Files

**momaka** · 11-07-2015, 06:03 PM

Re: Acer G235H Abid (dead) no indicator LED

Originally posted by Dogcatdog View Post

Today i replaced also all the caps on the main board,symptoms are still the same. unchanged, i checked if anything gets worm or hot, but there is nothing, not even warm, so no change in temperature, i also checked the HDMI port, and checked also the DVI and VGA if there is anywhere a short, but there was no short.

That is very strange. At least the regulators should get a little warm after the monitor has been left plugged in for 5-10 minutes. I don't know what to else to suggest for the logic board other than checking all resistors and ceramic capacitors on it - that is, make sure the resistors aren't open-circuit and that the ceramic capacitors are not short-circuited. But I don't know at this point if this is worth your time or the value of the monitor, so this is optional.

Originally posted by Dogcatdog View Post

here the pictured of the on/off panel board, i checked also the resistors and also wrote in the pics the markings and DMM measurements

Great work labeling everything. Really makes it easy to give help, so big thank you for that.

I checked the SMD resistor codes with this online tool:
http://www.resistorguide.com/resistor-smd-code/
... and it seems that your resistors values are in specs. That is:
01d = 100 KOhms
18c = 15 KOhms
563 = 56 KOhms

And yes, all of the small tan components that look like sand grains and are marked Cxxx are ceramic capacitors indeed. Just make sure they are *not* showing short-circuit on your multimeter.

Other than that, I don't know what else to suggest. Perhaps try pressing the "Auto" button or maybe some button combinations to see if that will make the monitor wake up.

I've seen this "no LED" issue on other monitors before, but it is almost always bad caps in PSU, bad caps on logic board, or a bad regulator on logic board. Since you recapped the PSU and checked the voltages on the voltage regulators, that eliminates these issues from the list.

**stj** · 11-07-2015, 06:12 PM

Re: Acer G235H Abid (dead) no indicator LED

test the led.
seriously - had bad led's on LG stuff before!

**Dogcatdog** · 11-08-2015, 05:58 AM

Re: Acer G235H Abid (dead) no indicator LED

Today i replaced all the Electrolytic capacitors on both boards, no change.

I Checked again if something gets warm, left the Monitor on for ca. 30 mins. but no difference, nothing is getting warm or hot.

I checked all the resistors on the logic board and all seem fine, cant tell 100%, there are no marking on them, same goes for the tiny capacitors.

Since im doing this for educational personal reasons and would like to learn more about this, i have time and patience.

please let me know what else i could test and how.

thank you very much in advance

Originally posted by momaka View Post

That is very strange. At least the regulators should get a little warm after the monitor has been left plugged in for 5-10 minutes. I don't know what to else to suggest for the logic board other than checking all resistors and ceramic capacitors on it - that is, make sure the resistors aren't open-circuit and that the ceramic capacitors are not short-circuited. But I don't know at this point if this is worth your time or the value of the monitor, so this is optional.

Great work labeling everything. Really makes it easy to give help, so big thank you for that.

I checked the SMD resistor codes with this online tool:
http://www.resistorguide.com/resistor-smd-code/
... and it seems that your resistors values are in specs. That is:
01d = 100 KOhms
18c = 15 KOhms
563 = 56 KOhms

And yes, all of the small tan components that look like sand grains and are marked Cxxx are ceramic capacitors indeed. Just make sure they are *not* showing short-circuit on your multimeter.

Other than that, I don't know what else to suggest. Perhaps try pressing the "Auto" button or maybe some button combinations to see if that will make the monitor wake up.

I've seen this "no LED" issue on other monitors before, but it is almost always bad caps in PSU, bad caps on logic board, or a bad regulator on logic board. Since you recapped the PSU and checked the voltages on the voltage regulators, that eliminates these issues from the list.

**Dogcatdog** · 11-08-2015, 05:59 AM

Re: Acer G235H Abid (dead) no indicator LED

Thank you very much for the reply, i have tested the LED, and it works i.e. its not broken, any other ideas?

Originally posted by stj View Post

test the led.
seriously - had bad led's on LG stuff before!

**selldoor** · 11-08-2015, 09:51 AM

Re: Acer G235H Abid (dead) no indicator LED

If we are now clutching at straws are you testing with it all connected up and a known
working source connected
Have the back lights ever flashed at all?
When you "picked it up" was it thrown out or did whoever you got it off say what they thought had happened to it?

edit- can you post a better picture of the back of the board with better lighting and no flash - do it in 2 halves
if needs be.

**Dogcatdog** · 11-09-2015, 05:24 AM

Re: Acer G235H Abid (dead) no indicator LED

hi and thank you for the comment, yes i tried all things with panel attached and without.

I have no information on what happened to the display, since i plugged it in the first time nothing changed, it was always exactly the same symptoms.

i attached additional pictures, please let me know if these are better, thank you very much for the help in advance.

Originally posted by selldoor View Post

If we are now clutching at straws are you testing with it all connected up and a known
working source connected
Have the back lights ever flashed at all?
When you "picked it up" was it thrown out or did whoever you got it off say what they thought had happened to it?

edit- can you post a better picture of the back of the board with better lighting and no flash - do it in 2 halves
if needs be.

Attached Files

**selldoor** · 11-09-2015, 08:43 AM

Re: Acer G235H Abid (dead) no indicator LED

The pictures are not really clear enough for troubleshooting. Lighting is the key.
They need to look like the ones in this post https://www.badcaps.net/forum/showpo...94&postcount=1 just the back of the Power supply will do.
Something to try -you may need an assistant - start with no power to the boards -set your meter on DCV20 and place the black probe on a ground screw
and the red probe on the on/off pin mentioned by Momaka in post 6. Connect the power
to the board - does anything register on the meter? with the meter still in place then press the button to switch the monitor on- again does anything register on the meter.

**Dogcatdog** · 11-10-2015, 07:35 AM

Re: Acer G235H Abid (dead) no indicator LED

Hi and thank you for the reply, i tried what you have suggested on the powerboard the on/off labeled pin and one probe to ground/chassis there is no change it shows 0V no matter if i press the button or not, all that i have checked with all connected to the panel, and also tried it without the panel, same result.

here the requested pictures i hope they are sufficient, it is very hard to take pictures since the light gives always a glare and i really dont know how to avoid it, i took several pictures tried to merge them together, and also tried to make an HDR image i hope one of these is good, if not i will take some more pictures, thank you very much in advance and for the help

ps. i had to convert it into a PDF(its around 18MB) because it seems not to accept the jpg files which are between 2 and 4mb there are 14Pictures in the PDF and the PDF is not accepted either maybe the forum has a problem or i exceeded limit, i dont know. anyway i uploaded everything on https://mega.nz/#F!OJ5EWZ4K!coLLXMaS-SdymvZS0_BZYA

thanks again in advance

Originally posted by selldoor View Post

The pictures are not really clear enough for troubleshooting. Lighting is the key.
They need to look like the ones in this post https://www.badcaps.net/forum/showpo...94&postcount=1 just the back of the Power supply will do.
Something to try -you may need an assistant - start with no power to the boards -set your meter on DCV20 and place the black probe on a ground screw
and the red probe on the on/off pin mentioned by Momaka in post 6. Connect the power
to the board - does anything register on the meter? with the meter still in place then press the button to switch the monitor on- again does anything register on the meter.

**Dogcatdog** · 11-10-2015, 08:47 AM

Re: Acer G235H Abid (dead) no indicator LED

here also the images on imgur, http://imgur.com/a/CxZK2/all that took ages to upload.

thank you in advance for any help and tips

**stj** · 11-10-2015, 10:15 AM

Re: Acer G235H Abid (dead) no indicator LED

i'v not been following this, but it may be time to get digital.

do you have a way to check the crystals on the logic board?

**Dogcatdog** · 11-10-2015, 11:19 AM

Re: Acer G235H Abid (dead) no indicator LED

thank you for the reply

unless i can do that with a no name DMM, i guess i have no way to test it, i do not own an oscilloscope.
but if something like this works and makes sense in generally then i guess i could buy one http://www.ebay.com/sch/i.html?_from...DSO138&_sop=15

thanks for the info in advance

Originally posted by stj View Post

i'v not been following this, but it may be time to get digital.

do you have a way to check the crystals on the logic board?

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