Issue with acer v173 CCFL inverter

[waldoalvarez00]

Hi people:

This is not a repairing issue. Actually the monitor is perfectly fine. It is an acer v173. Thing is I am trying to transform it into a TV using an universal TV control board.

Well thing is am trying to reuse the inverter from the monitor board. It is combined with the power source. I am not sure if I can get 12v from it but was thinking to at least reuse the monitor inverter and save some money while learning.

So I measured the pins and saw the original controller board was sending about 2.8v to one pin to turn on the inverter.

So I took some resistances and made a voltage divider out of the 5 volts it sends from the power source.

Thing is it turns on but goes sort like flickering and eventually turns off.

Now strange thing is if I connect the controller board with only +5v and ground (rest of the pins disconnected) once I apply the voltage to the on pin it turns on without problems. If I don't stop sending the voltage and turn off the controller board it goes into the flickering thing.

So I am wondering what could be the cause and trying to get some hints here.

[waldoalvarez00]

Re: Issue with acer v173 CCFL inverter

I did two tests too. I used a resistor between +5 volts and ground to simulate some load. Same result. Also putted large electrolytic capacitor at +5v and ground just in case the signal was sort like becoming unstable. Same thing. So I am wondering for possible cause.

[waldoalvarez00]

Re: Issue with acer v173 CCFL inverter

Here is the service manual

I see the brightness pin provides a PWM signal. Now strange thing if I remove that pin the inverter turns on quite fine. Both with controller sending the signal and with voltage applied manually by me (the pin removed from controller board). I am wondering. Could be some sort of coupling effect somewhere? Cause in theory I am removing that PWM signal. What would be voltage level and frequency of such signal? No scope at hand here. Also what would be cheapest way to generate that PWM? Maybe this http://www.instructables.com/id/Yet-...rato/?ALLSTEPS . I am willing to do some tests. This is more than anything a learning thing. To gain experience. So lets say buying a 5 USD inverter at ebay would solve the thing but won't be too interesting.

[waldoalvarez00]

Re: Issue with acer v173 CCFL inverter

Here is the microcontroller datasheet http://compcar.ru/forum/attachment.p...1&d=1285841596 The voltage level of that signal should not be higher than 3.3v since that is what feeds the chip and the frequency must be between 100 Hz and 100k.

[budm]

Re: Issue with acer v173 CCFL inverter

When you remove that PWM dimming control, the backlights brightness will be at full (100% duty cycle PWM signal, 3.3V).
From service manual.
Brightness PWM duty 35%~100%
*PWM:High=3.3V(3.00~3.60V),Low=0.0V,Frequency=4.0*V-Freq(Hz)
So if you have 0V then the backlights will not be on, the duty cycle range is from 35% ~100%.

So what Voltage do you have on the PWM control pin?
50% duty cycle = 3.3V *0.5 =1.65VDC.
Most monitors use about 200~300Hz for the PWM dimming frequency (spec sheet of the IC* Three channels of PWM DAC with programmable frequency from 100K to 100Hz.)

[waldoalvarez00]

Re: Issue with acer v173 CCFL inverter

When you remove that PWM dimming control, the backlights brightness will be at full (100% duty cycle PWM signal, 3.3V).
From service manual.
Brightness PWM duty 35%~100%
*PWM:High=3.3V(3.00~3.60V),Low=0.0V,Frequency=4.0*V-Freq(Hz)
So if you have 0V then the backlights will not be on, the duty cycle range is from 35% ~100%.

So what Voltage do you have on the PWM control pin?
50% duty cycle = 3.3V *0.5 =1.65VDC.
Most monitors use about 200~300Hz for the PWM dimming frequency (spec sheet of the IC* Three channels of PWM DAC with programmable frequency from 100K to 100Hz.)

I have 0v at that pin. And that is what's strange. If I remove all pins from the controller board except +5v and ground, I turn it on and I apply 2.8 volts to the ON/OFF pin, the inverter turns on like a charm. If I turn off the board and keep applying the 2.8 volts it starts to flicker. Eventually it turns off seems some protection circuit triggers.

[budm]

Re: Issue with acer v173 CCFL inverter

The PWM line on the power supply/Inverter board has the pull-up resistor to pull PWM LINE HIGH, the output of the MICRO controller IC does the PWM switching and it stuck ON so the output is at GND right now.

[waldoalvarez00]

Re: Issue with acer v173 CCFL inverter

The PWM line on the power supply/Inverter board has the pull-up resistor to pull PWM LINE HIGH, the output of the MICRO controller IC does the PWM switching and it stuck ON so the output is at GND right now.

Sorry I don't understand well. What you suggest? Just ignore the issue and provide a 3.3v level PWM signal with 200-300 Hz right.

[budm]

Re: Issue with acer v173 CCFL inverter

You can leave the PWM wire unconnected which will drive the lamp at full brightness at all time which is not a good idea.
You have to come up with circuit to drive the transistor with PWM signal based around 200 or 300 Hz and able to adjust the pulse width betwen 35~100% range.

[waldoalvarez00]

Re: Issue with acer v173 CCFL inverter

I did some more things. I measured again the voltage in that line with the meter. It was 0.28v from the control board. Also I wired a transistor tester (http://www.banggood.com/GM328A-Trans...-p-997582.html) putted it with a resistor and the duty at 50% and measured so I got a 1.7 volts read just to make sure the line was around the expected voltage (3.4v). So I connected that line of the tester to the PWM line (no idea on the frequency of the tester) and got the same thing.

[budm]

Re: Issue with acer v173 CCFL inverter

I did some more things. I measured again the voltage in that line with the meter. It was 0.28v from the control board. Also I wired a transistor tester (http://www.banggood.com/GM328A-Trans...-p-997582.html) putted it with a resistor and the duty at 50% and measured so I got a 1.7 volts read just to make sure the line was around the expected voltage (3.4v). So I connected that line of the tester to the PWM line (no idea on the frequency of the tester) and got the same thing.

What do mean you got 'THE SAME THING'?
If you do not disconnect the PWM wire going back to the MAIN/LOGIC board first then the MAIN/LOGIC board will keep that line low and will not allow that PWM signal to go high/low when you try to use external PWM source.

[waldoalvarez00]

Re: Issue with acer v173 CCFL inverter

Yes of course I disconnected the PWM wire from the logic board. Both where disconnected. When I put high the ON/OFF line it turns on ok (PWM disconnected as well). When I disconnect the logic board and pass PWM from the tester to the inverter board and rise the ON/OFF line to 2.8v it turns on but goes flickering (no idea on frequency coming from the tester). I was thinking maybe generate square wave from the tester at that specific frequency (200 - 300 Hz) and see what happens. Should be sort like a 50% duty cycle signal.

[waldoalvarez00]

Re: Issue with acer v173 CCFL inverter

ok the tester frequency is around 7 kHz

[waldoalvarez00]

Re: Issue with acer v173 CCFL inverter

Never figured out with this one so I left it as Monitor. I transformed some others. I even fixed one that had a bad cap in the inverter. I am thinking that for PWM inverters I can use an attiny since is relatively cheap and easy to read with ADC an analog input and translate it to PWM (yes I know some OPAmp can do it in comparator mode but can take more work and chips).