Acer G235H Abid (dead) no indicator LED

[stj]

Re: Acer G235H Abid (dead) no indicator LED

does the meter have a frequency setting?

[Dogcatdog]

Re: Acer G235H Abid (dead) no indicator LED

btw since this seems to be a kit, i guess it will not be easy to assemble, and there is no guarantee that something is screwed up in the kit or board so i wonder if it makes any sense to buy that? in addition maybe its no good at all

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

[Dogcatdog]

Re: Acer G235H Abid (dead) no indicator LED

i really dont know much about oscilloscopes, what functions they need and which are good, also i wonder if i assemble it, then i would need to calibrate it/test it?
ofc i would like to avoid to buy something that i have not much use for and worse something that does not even work as it should be
here a website with more info i guess you know and understand better than me

http://www.jyetech.com/Products/LcdScope/e138.php

im sure there are more websites with info of it, it seems to be some open source thing



thank you in advance,

does the meter have a frequency setting?

[stj]

Re: Acer G235H Abid (dead) no indicator LED

forget cheapy scopes, a scope must run atleast 5 times faster than the crystal your checking.
and crystals regularly go over 25Mhz - you do the math!

you can get frequency counters on ebay from china for about $15 but i'm not sure it's worth it for one tv it may not fix.

[selldoor]

Re: Acer G235H Abid (dead) no indicator LED

I will try and look in detail at the pictures later but at first glance they are not much improved. As a general rule we need to be able to read the part numbers on the board. Some of the solder joints do not look great. I can at least read the board number on the label now so will try and find a picture online.
It sounds like the mainboard is not sending a signal. Led being out is also a sign of a bad main board.
Another test/trick is if you have a 600ohm to 1kohm resistor try putting it between the 5v pin and on/off pin then plug in and switch on. Again you are looking to see if the screen flashes and as before also try with the panel disconnected from the main.

Also if you can find a 6v auto/car bulb try it between the 5v pin and ground. to see if it lights or lights then goes dim. (sometimes a voltage tests good with no load)

[Dogcatdog]

Re: Acer G235H Abid (dead) no indicator LED

thanks for the tip, i did the tests you have suggested, just to make sure i did not make a mistake i will explain what i did, i took a 1k Ohm resistor color code brown/black/orange/gold and bridged the brown wire which is marked on/off on the powerboard to the the red wire which is marked 5v on the powerboard, and did that on the main board side with the mainboard attached, it lit up and showed me some color bars, then white grey and black
it did repeat those pattern non stop, i tried it with the on/off front panel attached and without it was same thing and pressing the button did not influence the voltage on the brown on/off pin which was 4v with the 1kOhm resistor., so the panel is fine and the backlight works too, and i have a repeating pattern, so is the problem somewhere on the main board?
i have also tried the 6v bulb thing, it gives constant same voltage and it does not go dimm.

thank you in advance.

_

I will try and look in detail at the pictures later but at first glance they are not much improved. As a general rule we need to be able to read the part numbers on the board. Some of the solder joints do not look great. I can at least read the board number on the label now so will try and find a picture online.
It sounds like the mainboard is not sending a signal. Led being out is also a sign of a bad main board.
Another test/trick is if you have a 600ohm to 1kohm resistor try putting it between the 5v pin and on/off pin then plug in and switch on. Again you are looking to see if the screen flashes and as before also try with the panel disconnected from the main.

Also if you can find a 6v auto/car bulb try it between the 5v pin and ground. to see if it lights or lights then goes dim. (sometimes a voltage tests good with no load)

[Dogcatdog]

Re: Acer G235H Abid (dead) no indicator LED

i know it looks ugly, but this time the traces are very visible. it is composed of 4 seperete pictures hence the different exposure in the 4 sections of the one picture, but now the whole thing is visible
thank you in advance
if this one is still not good enough i will try again

[selldoor]

Re: Acer G235H Abid (dead) no indicator LED

There look to be one or two poor solder joints on the transformers and
some of those you have done on the caps look a bit grey (not shiny) but
as the screen did light up I guess the power supply is ok.
The cycling through the colours might be part of a self test. Did you have a working PC connected? At least you can tell if the screen is not damaged and the backlight works. Did you try pressing the menu button?
Looks like it may be the main board but it is very difficult to test all the tiny components on it so replacement is the usual step. They look quite expensive v the value of the monitor perhaps try and find a seller who will let you return it ,if it doesnt work?

[Dogcatdog]

Re: Acer G235H Abid (dead) no indicator LED

thank you for the reply, yes i tried it with a working source but there was no change/the source video did not get there, it was just those test patterns, btw. i forgot to mention that those do not come up immediately, but after like ca. 10sec. after providing the display with power, i also tried for ca. 1 hour long several different button pressing configurations to see if there is anything happening, but there is nothing happening no matter what i push and how many times i do. to buy a new mainboard is not really worth it, the price is to high for it, any help/tip to fixing it on component level i would really appreciate, like how to eliminate what it could and could not be, what kind of component am i looking to test/replace for.

thank you in advance.

There look to be one or two poor solder joints on the transformers and
some of those you have done on the caps look a bit grey (not shiny) but
as the screen did light up I guess the power supply is ok.
The cycling through the colours might be part of a self test. Did you have a working PC connected? At least you can tell if the screen is not damaged and the backlight works. Did you try pressing the menu button?
Looks like it may be the main board but it is very difficult to test all the tiny components on it so replacement is the usual step. They look quite expensive v the value of the monitor perhaps try and find a seller who will let you return it ,if it doesnt work?

[Dogcatdog]

Re: Acer G235H Abid (dead) no indicator LED

so i decided to toss it into the oven for 8 mins at 230°C Celsius / 446 °F
to see if there will be any change at all, and well.. nothing no change at all...
i guess some component is dead and nothing helps but to find it? but what??

[Dogcatdog]

Re: Acer G235H Abid (dead) no indicator LED

i further rechecked the SMPS/PSU and by accident i tested for continuity of the 5v rail to ground, and there is a closed circuit, does that mean that i have somewhere a short to ground on the PSU? and that it actually might not be the mainboard but the PSU?
btw. it happens only when i plug the cord into the PSU without it the meter shows 117 in the diode mode, but as soon as i plug the power cord in it starts to beep and shows 266 whatever that means
ah yes that happens only when the psu is connected to the mainboard, well i guess then it is the mainboard that has somewhere a short to ground, that answers that, or at least i think that is what is happening. not sure anymore

[Dogcatdog]

Re: Acer G235H Abid (dead) no indicator LED

and it does not matter if the small power on/off board is connected to the mainboard or not it happens then anyway, but as mentioned above, only when the cord is plugged in

[Dogcatdog]

Re: Acer G235H Abid (dead) no indicator LED

so i believe to have found the fault in the mainboard, so i thought before i replace the LDO
uz1084l 3.3V, i thought i will turn it on and test it one more time, and to my surprise now there comes no voltage, so seems like the PSU got something shot. any ideas? i checked the bridge rectifier it seems fine, altough i had ca. 130V so i thought i will replace it with a knows good rectifier and did that, but strangely enough i get same voltage, i guess the rectifier is fine, but who knows

[Dogcatdog]

Re: Acer G235H Abid (dead) no indicator LED

nvm it was a bad solder joint that stopped the PSU/SMPS from working, now it works again, so i went ahead and replaced uz1084l 3.3V, with an identical one, and the symptoms are same, on the in pin(right 5V) i get a short to ground as soon as i plug in the power, is this normal? or is this the problem?please help thank you in advance

[Dogcatdog]

Re: Acer G235H Abid (dead) no indicator LED

in addition i might have forgotten that the short to ground is only when i check with the DMM with the positive probe to the chassis and the negative to the 5v rail, when i reverse the probes then it is not there, but as soon as i unplug the power cord while positive probe is on the chassis and negative on 5v pin, then the circuit drops to open, that is after a few seconds ca.2-4

[selldoor]

Re: Acer G235H Abid (dead) no indicator LED

Whilst I do not know what might be wrong with the main board, you can test the larger components and even small caps for shorts if you have the patience.
All the small switching transistors would have to be removed to test.
Your best bet might be to find a monitor on ebay with a broken screen and save on postage by asking them to remove and send only the main board.

What you DO need to do is to stop testing as you are without understanding what you are doing. As a basic rule

THE ONLY thing you test with the monitor powered up is voltage!!

NEVER test in diode mode or in resistance mode with the monitor powered up.

[Dogcatdog]

Re: Acer G235H Abid (dead) no indicator LED

thanks for the reply

first of all thank you very much for this great advice, i did not know better,

"What you DO need to do is to stop testing as you are without understanding what you are doing. As a basic rule

THE ONLY thing you test with the monitor powered up is voltage!!

NEVER test in diode mode or in resistance mode with the monitor powered"


i appreciate that very much

so i coult test the "small switching transistors" and the capacitors, do you mean the SMD capacitors? if so do they need to be unsoldered and then tested? i.e. if there is a short then they are dead? all the large components i have tested already except the RTL chip i do not know how to test that one since it has like 128 pins, but since there was a test pattern shown does it mean the chip is good? also the smd diodes do they need to be taken out of the circuit to be tested?

thanks for the advice about ebay yeah i thought about it, but it started to become a principle and would like to find out what the problem is,

thank you very much for the replies so far, very much appreciated and thanks again for the "THE ONLY thing you test with the monitor powered up is voltage!!"
tip.

Whilst I do not know what might be wrong with the main board, you can test the larger components and even small caps for shorts if you have the patience.
All the small switching transistors would have to be removed to test.
Your best bet might be to find a monitor on ebay with a broken screen and save on postage by asking them to remove and send only the main board.

What you DO need to do is to stop testing as you are without understanding what you are doing. As a basic rule

THE ONLY thing you test with the monitor powered up is voltage!!

NEVER test in diode mode or in resistance mode with the monitor powered up.