Acer B326HUL power supply dead

[Behemot]

Display only blinks and than stays dead. Check open the PSU revealed it is dead.

There are three output rails: winding to feed the TEA1791T synchronnous rectification controller (this thing has no connection with primary side!), the output for the rectification transistor - this rail feeds the signal board, and than backlight rail.

Seems like the unit only pumps few cycles to the secondary so voltage rises a bit and than falls down as the caps discharge. I have about 15.5 V on a small cap on the primary auxiliary rail just after the diode which slowly falls, pumps again to 15.5 V and that repeats.

There is however oscillating voltage between like 18 and 19.6 V on the cap directly in front of the primary common PFC/PWM controller. Do not think this is normal condition. Cannot identify the controller right now, it has layer of lackquer, gonna have to try removing it.

I do see only 320V on the input cap though, there is no spike suggesting the PFC would be turning on, so maybe the problem lays in here?

[Behemot]

It's very difficult to read anything in here but it seems like the PFC/quasi-resonant flyback controller is NXP, possibly TEA1751T. According to the datasheet, the startup voltage is 21-23 V so when it's at 18-19.6 that's too low.

The path goes from the auxiliary winding on primary side through inductor to an SMD diode, capacitor and than there is "K415 C200" TO-92 bipolar transistor. The 15V feed leads to its collector, the oscillating 18-19.6V output is on its emitter. Collector and base has 1002 SMD resistor in between and base is also connected through an SMD zener to return.

So it seems like some amplifier with zener feedback? And this is to feed the Vcc of the controller.

[fred41]

Originally Posted by Behemot

It's very difficult to read anything in here but it seems like the PFC/quasi-resonant flyback controller is NXP, possibly TEA1751T. According to the datasheet, the startup voltage is 21-23 V so when it's at 18-19.6 that's too low.

The path goes from the auxiliary winding on primary side through inductor to an SMD diode, capacitor and than there is "K415 C200" TO-92 bipolar transistor. The 15V feed leads to its collector, the oscillating 18-19.6V output is on its emitter. Collector and base has 1002 SMD resistor in between and base is also connected through an SMD zener to return.

So it seems like some amplifier with zener feedback? And this is to feed the Vcc of the controller.

I also have a dead power board, did you manage to find some datasheet, schematics, wathever informations about this card? Thanks

[budm]

If we can see some good clear pictures of the boards and how they are connected together, that will be a good starting point.

[fred41]

If you need more detailled pictures or anything else, ask.

Thanks

[fred41]

Originally Posted by budm

If we can see some good clear pictures of the boards and how they are connected together, that will be a good starting point.

Is it useful?

Thanks

[budm]

SO, what Voltages do you have on that white connector of the power supply board that goes to the logic/main board?

[fred41]

Originally Posted by budm

SO, what Voltages do you have on that white connector of the power supply board that goes to the logic/main board?

Hi, Budm

Thanks for your answer

I have no light on the front power push button.

I tested the general 220v power switch on the back, and the fuse.

And to answer your question, I have 0v on each wire on the white connector, with the board plugged or unplugged:

https://www.youtube.com/watch?v=8uVT8g2OchQ


I have 335Vdc arriving to the "120µF / 450V" capacitor, and I unsoldered it and tested it too:

https://www.youtube.com/watch?v=IL7uwboCR70


Hope I done everything right, and made myself understood, English is not my first language.

Thanks

[budm]

In your picture #2 on the bottom left, there is an IC (18-PIN?) there, can you read the P/N?

[fred41]

Hi, I tried to take pictures and read the part references



n°1 : NXP TEA1751T CDX12104 TXD14241

n°2 : MPS1431 MP3398 E44H2168A

n°3 : unreadable, but seems to be the same as n°2

thanks

[budm]

Originally Posted by fred41

Hi, I tried to take pictures and read the part references



n°1 : NXP TEA1751T CDX12104 TXD14241

n°2 : MPS1431 MP3398 E44H2168A

n°3 : unreadable, but seems to be the same as n°2

thanks

OK, #1 is the one we need to find out if it has DC Voltage between VCC pin and Gnd for it run or not. Please see the spec sheet.
NOTES: You will be working in the HOT DEADLY side of the circuit so do not touch ANYTHING with your hands or body, you should at least plug the monitor into GFCI outlet.

[fred41]

Originally Posted by budm

OK, #1 is the one we need to find out if it has DC Voltage between VCC pin and Gnd for it run or not. Please see the spec sheet.
NOTES: You will be working in the HOT DEADLY side of the circuit so do not touch ANYTHING with your hands or body, you should at least plug the monitor into GFCI outlet.

Thanks a loot for your answer, but I'm not sure what GFCI means exactly, is it an outlet with ground? I live in France , and this is the default wall outlet we have :



Am I right for where to test?

[Andrew F. Ali]

GFCI means Ground Fault Circuit Interrupter. This is an electrical outlet with Reset button and a Test button on it that should a shock hazard be detected it would switch the supply to the receptacle OFF.

[fred41]

Originally Posted by Andrew F. Ali

GFCI means Ground Fault Circuit Interrupter. This is an electrical outlet with Reset button and a Test button on it that should a shock hazard be detected it would switch the supply to the receptacle OFF.

Like this?



I have one

[Andrew F. Ali]

This is how our electrical GFCI outlets look like. The RED button is the RESET and the BLACK button is the TEST. So is a fault is detected the RED button pops up and disconnects the supply and to reset is to just push it back in. When the Test button is depressed the RESET button pops up and so we know the system is working.

[budm]

EURO GFCI outlet:
http://internationalconfig.com/icc6.asp?item=4721-10HG2

[budm]

Originally Posted by fred41

Thanks a loot for your answer, but I'm not sure what GFCI means exactly, is it an outlet with ground? I live in France , and this is the default wall outlet we have :



Am I right for where to test?

That is correct pin out for TEA1751:
Pin 1 = VCC
Pin 2 = GND

[Andrew F. Ali]

Originally Posted by budm

EURO GFCI outlet:
http://internationalconfig.com/icc6.asp?item=4721-10HG2

Thanks budm

[fred41]

Originally Posted by budm

OK, #1 is the one we need to find out if it has DC Voltage between VCC pin and Gnd for it run or not. Please see the spec sheet.
NOTES: You will be working in the HOT DEADLY side of the circuit so do not touch ANYTHING with your hands or body, you should at least plug the monitor into GFCI outlet.

I measured 18.5Vdc - 19Vdc

And I didn't blew up the house, nor I burned myself...

Thanks everyone

[the.norbulus]

Hi fred41, you and I seem to be in a similar fix. I have a Benq 32" with a dead psu and the board is similar to yours. Also the fault on mine seems to be in the same general area as yours (around the TEA1751)
Could you please tell me the value of the resistor on your board between pin 16 on the TEA1751 and the transformer? Mine has burnt out.
Have you had any luck getting yours going?

Here's my thread: https://www.badcaps.net/forum/showth...830#post890830