No power Benq G922HDAL

[srbax]

This monitor don't have power button light at all and no screen.
It won't react on power button at all.
I measured voltages of 5V and 18.88V on power board.
Mosfet (I think it is a mosfet) on back of power board is very hot and it stinks.
After checking, I think it is shorted, because ohm reading are 1.9, 8.8 and 9.9 ohm between pins.
Problem with that mosfet (210137BA 9T90101) is that I can't find datasheet for it, so I need your help.
Also can't find service manual for this monitor.
Also I think one diode is not good, because in both direction I have bad readings, beep sound in both directions.
What else could I check?

[Pentium4]

Re: No power Benq G922HDAL

Might as well check the main cap and the fuse as well. Were you measuring for 24V when you got 18.88V? And that thing on the back looks like a voltage regulator, it could be bad, you should check that and report the DC voltage on it going from left to right pins 1-3

[srbax]

Re: No power Benq G922HDAL

Fuse is ok. Voltage on main cap is 302 V. There is only 5V on one pin. 18,88 V is the voltage for other board. I'm not sure should it be 24 V.

[selldoor]

Re: No power Benq G922HDAL

Your pictures are really good -thanks.
Might be better to say which pin or which colour cable is
what voltage. Were the tests done with all the boards connected. Did you test the "faulty" diodes on or off the board.
If the diode is faulty the other voltages may not appear
until it is replaced.

One of the two caps c611 or c608 will be startup
caps - can you measure the voltage on them and say what v and uf they are.

302v is good on the big cap

[srbax]

Re: No power Benq G922HDAL

Thank you guys for Yours replies.
Caps has voltages 14.55 and 5.88. C611 10uf, 50V and C608 47uf, 25V.
On second pair of red wires for main board cable there is 5V.
On first two, also red wires, there is 18.88 V, for other board. I guess it is board for led backlight.
I noticed when monitor is powered on, on second pin of that, let say voltage regulator, there is 0.7 V and after some time it is 0 V. Bigger voltage is 19.7 V and it is dropping till 18.88 V. 5 V voltage is stable.
Diode is tested on board and it is circled in red on first picture.
I also measured voltages on voltage regulator on main board but they are 0.
Testing is done with all boards connected.

[retiredcaps]

Re: No power Benq G922HDAL

You should remove the suspicious components and retest them out of circuit.

I thought I found two shorted voltage regulators on a Dell board only to find out they were good once removed out of circuit.

[srbax]

Re: No power Benq G922HDAL

I replaced voltage regulator and it was shorted. There was smoke from new one too, so it's probably shorted.
I don't know what is causing it.
I supouse that voltage generator has to give 3.3 V to first pair of red wires to main board.
I noticed 3.3 V marking near connector on main board.

[srbax]

Re: No power Benq G922HDAL

I removed suspicious diode and measurements are 0.177 in one and 0L in other direction.
Is that good or not?
Other big diode has 0.39 in one and 0L in other direction.
I also checked all bigger caps, except main cap, and they have good values.

[ben7]

Re: No power Benq G922HDAL

From what I see there is one voltage regulator on the mainboard. It is circled in orange.

Try to detach the cable circled in green, and power on the monitor.

From the markings on the mainboard, the orange wires are 3.3v. The regulator on the power supply is for the 3.3v. So, there must a short on the 3.3v line...

[selldoor]

Re: No power Benq G922HDAL

Measure the voltages on the pads where the regulator should go.

[srbax]

Re: No power Benq G922HDAL

Finally I found free time to continue work on this monitor.
I checked voltages on pads of regulator and I measured 4.9 V between I and O pads and 5 V between G and I pads.
I don't think that is normal to have 4.9 V between I and O?

[ben7]

Re: No power Benq G922HDAL

Finally I found free time to continue work on this monitor.
I checked voltages on pads of regulator and I measured 4.9 V between I and O pads and 5 V between G and I pads.
I don't think that is normal to have 4.9 V between I and O?

Either there is a short, or the regulator is faulty. Most likely a short.

Measure the resistance from O to ground.

[srbax]

Re: No power Benq G922HDAL

I measured this without regulator on board and with other boards disconnected.

[jetadm123]

Re: No power Benq G922HDAL

Finally I found free time to continue work on this monitor.
I checked voltages on pads of regulator and I measured 4.9 V between I and O pads and 5 V between G and I pads.
I don't think that is normal to have 4.9 V between I and O?

I'm assuming that I=Input, G=Ground and O=Output. When you take voltage readings off a regulator, you make your measurements with repect to ground. You should be measuring the Output with respect to Ground. Looks like you measured across the Input and Output pins. To eliminate confusion do this: use a mounting screw for your negative probe and probe each pin of the regulator with your positive probe and report your results.

[srbax]

Re: No power Benq G922HDAL

You were right.
I've done measuring like You told me I=5V, G=0V and O=0.414V.
I did it without regulator on board because it was shorted and I'm not sure for replacement.
Can You suggest me appropriate voltage regulator for replacement?

[jetadm123]

Re: No power Benq G922HDAL

What's the part number stamped on the bad regulator?

[srbax]

Re: No power Benq G922HDAL

210137BA 9T90101
I couldn't find something like that on internet.
Based on connector on logic board it has to deliver output of 3.3 V.
I found something similar, only based on input and output and layout of G, I and O.
It's LM3940IMP-3.3.
Regarding Your experience, what could be appropriate?

[jetadm123]

Re: No power Benq G922HDAL

Yes, looks like a good match. You need to verify one more thing: that the tab at the top of the regulator is also ground (G). With power off and monitor unplugged and your meter set to 200 ohms, place one probe on the middle pin and the other probe on the tab. You should see approx. 0 ohms. This means they are internally connected.

[budm]

Re: No power Benq G922HDAL

As requested by BEN7 on post12, With the regulator still remove, you should take the resistance reading between ground and the 'O' pad to see if it has real low resistance reading, just to make sure you have low output voltage from the regulator is not due to shorted load.

[srbax]

Re: No power Benq G922HDAL

There is 250 kohms between O and G and it's rising.
I did this measurement without voltage regulator on board.
After that I connected logic board and there is 9 ohms between O and G.
It is the same value that I measured between 1. and 2. pin of voltage regulator on logic board.
Is it possible that voltage regulator on logic board is also shorted?
It has similar marking as the bad one from power supply board: 210137DA 9T90171.