DELL P2210 - SMPS +5V reads ~+3.5V

[Agent24]

Do you have a service manual for this new revision model? Photos would help greatly! Show the PSU and other boards, how they connect, the burnt resistor etc.

Can't do much without knowing what the thing looks like.

[o3365566]

Originally Posted by fzabkar

ISTM that the dual MOSFET at U2 (P6006HVG) could be shorted. I would resolder all the pins of transformer T1 and check for shorts on the HV side.

I think you're right... again!
The dual MOSFET seems shorted. I will try to replace it and see.

Spare parts are on the go. I will write back as soon as I receive them.

Off topic: I reassembled the LCD panel after months and I forgot the right order of the different layers. What I did is (bottom-up):
1. White sheet
2. Fiber optic glass
3. Slim plastic sheet
4. Mylar sheet
5. Thick plastic sheet

I think everything is good but I have some doubts about 3, 4 and 5.
I wonder if the slim plastic was inverted with the thick.
As for the Mylar side, I had the impression that one side is reflecting but not the other.
Reflective one goes up or down? At the moment I placed it down...

[o3365566]

Originally Posted by Agent24

Do you have a service manual for this new revision model? Photos would help greatly! Show the PSU and other boards, how they connect, the burnt resistor etc.

Can't do much without knowing what the thing looks like.

Unfortunately I don't have the service manual for this revision.

At the moment I think I found failed components but if the problem is not solved I will post some photos.

[fzabkar]

Sorry, I've never disassembled an LCD panel. Best of luck.

[Agent24]

All I can say is it sounds like you have 1 and 2 correct, not sure of the others, I always keep them in order as I take them out of the panel so I never actually looked at which way they go.

Probably you'll just have to try it and see... if you get it wrong the image will be incorrect\inverted\missing. If it is, swap them around and try again.

[o3365566]

Originally Posted by o3365566

I think you're right... again!
The dual MOSFET seems shorted. I will try to replace it and see.

Spare parts are on the go. I will write back as soon as I receive them.

Off topic: I reassembled the LCD panel after months and I forgot the right order of the different layers. What I did is (bottom-up):
1. White sheet
2. Fiber optic glass
3. Slim plastic sheet
4. Mylar sheet
5. Thick plastic sheet

I think everything is good but I have some doubts about 3, 4 and 5.
I wonder if the slim plastic was inverted with the thick.
As for the Mylar side, I had the impression that one side is reflecting but not the other.
Reflective one goes up or down? At the moment I placed it down...

Hi,
Little update. First display is ok but the second one keeps burning dual Mosfet. Inverter and motherboards seems to work ok for about 5 seconds but after that Mosfet is shorted again and power led goes off.

About display layers everything is OK but the Mylar reflective side must be placed face up.

[bgaservis]

Interestigly I have one dead PSU here also.
D855 was shorted, changed but still no power. I think I got also low 5v.

[bgaservis]

Update, all sec. voltages are low at fluctuating 1.5v. It looks like there is some short somewhere...

[Agent24]

Check for shorts to ground across each output rail. Maybe a bad diode on another rail. Capacitors fail shorted too, sometimes. Test without the logic board etc connected to be sure it's the PSU and not the load.

Could also be bad primary side controller circuit is power cycling from bad Vcc capacitor or diode, or even bad controller.

Can you upload photos? Doesn't seem to be any in this thread so far.

[bgaservis]

All diodes check fine. There are no shorts on voltage outputs on +5v, +12v or +16v.
The diode that was shorted were on the +16v output.
U2 Dual mosfet is also fine.

There is audible clicking noise coming from somewhere on the board.
On second reading there are ~ 3.5v on the 5v rail, 9.5v on 12v rail and 12.5v on 16v rail.

[Agent24]

The clicking is probably from the main transformer as the primary-side controller starts up, shuts down, and starts up over and over.

Could be the controller supply, check C878, D852, R856

[bgaservis]

C878 have fluctuating voltage 12~14v
D852 and R856 are ok.

[Agent24]

Check the voltage on the main filter capacitor and ensure it stays steady. If it were bad you may get this problem.

Could be a feedback issue. Try checking\changing I850 and I851.


But I wonder if something on the 12v or 16v rails is still bad, leaky perhaps, or failing under load.

You could try lifting one leg of D855, D880, D881 and also R862 and R880 to disconnect those rails and see if that gives you a stable 5v.

[Agent24]

Originally Posted by o3365566

Hi,
Little update. First display is ok but the second one keeps burning dual Mosfet. Inverter and motherboards seems to work ok for about 5 seconds but after that Mosfet is shorted again and power led goes off.

Check the components C23, C22, R29, R30, C34 and C40?
Perhaps there is a problem there.

Maybe the U1 controller is bad, OR it's getting bad feedback to VSEN pin 9? Check ZD3 and associated parts perhaps. Maybe something wrong with C33\C35.

Can you check the inverter transformer winding resistances between the working and bad boards?

In fact, you could check multiple places and compare. For example, do all the pins of U1 on the bad and good boards measure the same resistance to ground\Vcc etc?

[bgaservis]

Originally Posted by Agent24

Check the voltage on the main filter capacitor and ensure it stays steady. If it were bad you may get this problem.

Could be a feedback issue. Try checking\changing I850 and I851.


But I wonder if something on the 12v or 16v rails is still bad, leaky perhaps, or failing under load.

You could try lifting one leg of D855, D880, D881 and also R862 and R880 to disconnect those rails and see if that gives you a stable 5v.

Main filter capacitor has around 310v on it ( it's measured 86uF ).

I have tryed to resolder diodes and resistors on 12v and 16v rails but it's still the same.

U850 has problem starting, I will try changing optocoupler and TL431 on feedback.

Tnx!

[Agent24]

Originally Posted by bgaservis

I have tryed to resolder diodes and resistors on 12v and 16v rails but it's still the same.

I don't mean resolder them, I mean disconnect them, to see if the circuitry on the 12/16v rails is not somehow at fault.

[bgaservis]

Originally Posted by Agent24

I don't mean resolder them, I mean disconnect them, to see if the circuitry on the 12/16v rails is not somehow at fault.

Yes, that's what I did, sry typo...

[Agent24]

Looking again at the schematic, ZD881 could cause the problem if it were leaky\shorted.
Another idea might be the current sense resistor, R869, if it has increased in value.

But, last time I had a PSU fault like this I checked everything and eventually found the controller was bad.

[Kalina]

Originally Posted by bgaservis

Interestigly I have one dead PSU here also.
D855 was shorted, changed but still no power. I think I got also low 5v.

Have you repaired your monitor? If so, what was the problem?