BenQ T201WA (4H.09C02.A01 power board) doesn´t turn on

[blackrider1]

Hello,one day ago, when I turnned my pc off, the power led of this monitor stayed orange with no response on pressing the switch.
I switched it on again and it was working fine, but when I pressed the power switch (of the LCD) instead of turning ON/OFF, it just showed me the bright control panel.
I disconected the power from the wall, and now, it doesn´t turn on anymore.
I checked fuse F601 (OK) Bridge rectifier BD601 (OK) and filter cap C605 (OK)
When checking IC601 (NCP1203P60) I´m getting 10 vcc at pin 6. Is it a normal meassure? Should I get between 16 & 20 vcc?
This board has these ELLITE crappy caps but all of them seems to be OK.
I can´t find any schematics for this board although I know it is used in, at least, ASUS VW222S & FP222W BenQ.
What do you advise me to test now? Remember that the power led doesn´t turn on.
I can´t test CN701 because I don´t know the pinouts values.
By the way, I resoldered everything to avoid cold solders.
Thanks

[PlainBill]

Re: BenQ T201WA (4H.09C02.A01 power board) doesn´t turn on

Hello,one day ago, when I turnned my pc off, the power led of this monitor stayed orange with no response on pressing the switch.
I switched it on again and it was working fine, but when I pressed the power switch (of the LCD) instead of turning ON/OFF, it just showed me the bright control panel.
I disconected the power from the wall, and now, it doesn´t turn on anymore.
I checked fuse F601 (OK) Bridge rectifier BD601 (OK) and filter cap C605 (OK)
When checking IC601 (NCP1203P60) I´m getting 10 vcc at pin 6. Is it a normal meassure? Should I get between 16 & 20 vcc?
This board has these ELLITE crappy caps but all of them seems to be OK.
I can´t find any schematics for this board although I know it is used in, at least, ASUS VW222S & FP222W BenQ.
What do you advise me to test now? Remember that the power led doesn´t turn on.
I can´t test CN701 because I don´t know the pinouts values.
By the way, I resoldered everything to avoid cold solders.
Thanks

Excellent job of troubleshooting, and the labeled pictures are a big help. Getting really nit-picky, I prefer working with pictures where the board has been flipped left to right rather than top to bottom. The next biggest problem is a few spelling errors. If I were grading, you'd get a high 'A'.

There are a few points you have missed. It IS possible to measure the voltages on CN701; it would be harder to establish what the voltages should be. Here's a summary, reading from left to right.

Pin Function

1 N/C
2-3 V1 (probably 5 volts) out
4-6 GND
7-8 V2 (probably 12 volts) out
9-12 Inverter and audio amp controls

10 volts at pin 6 is indeterminate - it's below the startup threshold, but within the operating range. What you neglected to say is if the voltage is steady, or if it changes.

As a PRELIMINARY diagnosis, IC601 is defective. It generates Vcc for startup internally, SMPS controllers that do this tend to have a high failure rate. Another possibility is the startup cap (C606 or C611). And it might be a short on one of the outputs.

These are the points to check

1 Voltage on IC601, pin 6. If it pulses, the IC is probably good.
2.Voltages on CN701 pins 2-3 and 7-8. If they both pulse, the ouput diodes are probably good.
3. With power off, check the resistance from V1 to Gnd and V2 to Gnd.

PlainBill

[blackrider1]

Re: BenQ T201WA (4H.09C02.A01 power board) doesn´t turn on

Thanks PlainBill.
Well, voltage on pin 6 is, when off, always 10,23 v and no pulses. I say when off because now it´s working again!!!!!
I reassambled everything, like in the picture and the power switch worked.
I´ve been able to start it up.Then I´ve turned it off and it keeps on not working.
I´ve tried to read again the voltage at pin 6 (10,23v) and when trying to switch it on again, it has worked again (weird!!).
Now the LCD is on, with the green power led on, but not responses when pressing it. It doesn´t switch the LCD off. I´m getting 14,29 v at pin 6 right now.
Everything works fine except switching ON/OFF.
May be something related to minimum and maximus working vcc of the IC, that causes IC to be blocked?
Now is on, so if you want me to check anything else while working, just tell me.
By the way, resistance between V1/GND and V2/GND was decreassing from 13-14 to cero (I stopped testing at 4 or 3) in about 2 minutes, I mean, slowly.
Thanks

[PlainBill]

Re: BenQ T201WA (4H.09C02.A01 power board) doesn´t turn on

Thanks PlainBill.
Well, voltage on pin 6 is, when off, always 10,23 v and no pulses. I say when off because now it´s working again!!!!!
I reassambled everything, like in the picture and the power switch worked.
I´ve been able to start it up.Then I´ve turned it off and it keeps on not working.
I´ve tried to read again the voltage at pin 6 (10,23v) and when trying to switch it on again, it has worked again (weird!!).
Now the LCD is on, with the green power led on, but not responses when pressing it. It doesn´t switch the LCD off. I´m getting 14,29 v at pin 6 right now.
Everything works fine except switching ON/OFF.
May be something related to minimum and maximus working vcc of the IC, that causes IC to be blocked?
Now is on, so if you want me to check anything else while working, just tell me.
By the way, resistance between V1/GND and V2/GND was decreassing from 13-14 to cero (I stopped testing at 4 or 3) in about 2 minutes, I mean, slowly.
Thanks

Strange behavior; it almost sounds like a bad solder connection.

One point; you misunderstand the function of the power switch. The power supply is on whenever the power cord is plugged it. The power button instructs the GPU (on the signal board) to turn the LCD panel, backlights, and power LED on or off.

PlainBill

[blackrider1]

Re: BenQ T201WA (4H.09C02.A01 power board) doesn´t turn on

I know it is an strange behaviour. When I get no response of the power button, if I test the 6 pin of the 1203P60 and try the power button again, it works!!!
For instance, when I´m unplugging the power cord and plugging it again, it is not working ( I mean the power button) but if I use the tester to checking vcc between negative pin of the filter cap and IC 6 pin, it works again, so I think the IC is bad, it can´t get the minimum vcc to start, but with the tester,somehow, it´s getting the neccesary charge to start, or a kind of resetting itself.
What do you think? Can this behavioour be due to bad caps? Or definitively to a bad 1203P60 IC?
Right now the button is working fine, is switches ON/OFF.
Maybe be a deffective button? It sounds ok when pressing it (I mean the click sound) and all the solder points are OK.
Or maybe due to a protection built desing of this IC?
Although I think you´ll have its datasheet I´m uploadding it.
Thanks

[PlainBill]

Re: BenQ T201WA (4H.09C02.A01 power board) doesn´t turn on

The real problem is you have incompatible results. If the power LED is orange, the power supply must be working. If the power supply is working, measuring the voltage on pin 6 should not have any effect on the power supply outputs.

I am really interested in the voltages out of the supply, both when it is responding to the power button and when it isn't. And if I had it on my bench, the first thing I would do is a complete recap of the power supply.

PlainBill

[blackrider1]

Re: BenQ T201WA (4H.09C02.A01 power board) doesn´t turn on

Do you mean voltages at CN701?

[PlainBill]

Re: BenQ T201WA (4H.09C02.A01 power board) doesn´t turn on

Do you mean voltages at CN701?

Yes, the voltages at CN701, especially the voltages on pins 2&3 and pins 7&8. Pins 4-6 are Gnd.

PlainBill

[Behemot]

Re: BenQ T201WA (4H.09C02.A01 power board) doesn´t turn on

Some guy asked me for help with this display. Before repair attempts, backlight ws not working at all.

After replacing all biger caps for Chemi-Cons LXZ, it works, but supposedly is blinking, or to be more precise, showing moving lines. Problem is reduced by setting frequency to 75 Hz, but still present. I am not really sure what could that be, any idea? Input cap should be fine acording to Atlas.