Dell F177FPE monitor, won't power on

[bfordz]

I've got a Dell F177FPE that went dead, it won't power on.
There's no power "on" light or anything.

I took it apart and the caps all 'look' good but they're all cheap Su'scon's or Teapo's.
While doing some basic tests of the board I found a Ceramic capacitor that shows open with the ohm meter, so I'm hoping that's the cause of my no power up problems. I included pics of the failed cap and it's location on the board.

My question / problem is I've never replaced or dealt with these type of capacitors so I want to know if I'm reading it correctly and my choice of replacement is correct. (based on what I've read)

The original is a JNC JN332M 250v and I'm not sure what the 440 x1 and 250 x2 means.
I've picked out a Murata Electronics DE1E3KX332MA4BN01F replacement.

I'm also going to replace all the Alum Elect Caps while I'm in there.

If there is anything else you notice, I'm open to suggestions.

[CapLeaker]

That is a snubber cap is supposed to read open. If it would have failed, you would see it. Since you don’t even have a stby led, probably the stby power rail that is always on is not working, or there is no AC going to the bridge rectifier. So check if you have about 170VDC on that main filter cap. Also the PFC needs to work (roughly 380VDC on the main filter cap) in order for the backlights to work.

[bfordz]

Well, that shows how much I know! Very little when it comes down to the real nitty gritty.

Most of my boards have all shown the issues, when it comes down to the actual 'what needs to be tested and the results' is where I get a bit lost.

When you say 'main filter cap' which one are you referring to?

[R_J]

Why don't you start by checking if the fuse is good or if you have any voltage across the main filter C854 (the blue 100µf/450v) capacitor. If you have 160vdc across the main filter, check the resistance of R852, it should be 0.2Ω
That cap you have circled has nothing to do with the operation of the power supply, it is a safety cap that connects the hot and cold grounds.

[bfordz]

The fuse is good and the R852 is 0.2ohms. I'll check voltage now.

[bfordz]

Main filter - 171.2vdc
R852 - 0.4ohms

[R_J]

D854 is the secondary dual diode, check the voltage across C862
If you have your +12 volts then the primary circuit is working, Check the voltage on U801 and U802, I don't know what there voltage should be, you may need to post the part numbers, I suspect one should output either +5v or +3.3v

Near the LVDS cable is a fet Q501, check if there is voltage on S and D, You also check the voltage on the Gate and see if changes when the power button is pressed.
You can also follow the wire from the power switch and see if there is any voltage on it and does it change when the button is pushed? If the microprocessor and eeprom U402 are getting VCC voltage you may have a corrupt eeprom causing the monitor to not turn on.

[bfordz]

12.07vdc

[bfordz]

U802
1 - 0.0v
2 - .433v
3 - 1.25v
4 - .433

U801 (no numbers but using same as 802)
1 - 0.0v
2 - not connected
3 - 5.20v
4 - 1.25v

that's checking voltage at each terminal not across terminals.

[R_J]

You can use some alcohol to clean the top of the ic so you can readthe numbers, or try looking at an angle, you may be able to read them, but the voltages don't look good.
The microprocessor operates from 3.3 volts, one of those regulators should be a 3.3 volt regulator

Without the regulator ic numbers it is hard to tell what the input and ouput voltages should be. I can see numbers on the ic's in your picture, what are the numbers?

[bfordz]

here's a diagram

[bfordz]

U801
a1
asiii7r-33
bo635 26

u802
ac 6i8l
17-18l

[R_J]

Those numbers can't be correct, Could it be a AS1117-33 If it is, it will be a 3.3 volt regulator
IC801 has +5volts on its input and only 1.25v on its output (it should be 3.3v) so something is loading it down

Also are you sure your model number is correct? I can't find it listed anywhere

[bfordz]

It is AS1117-33 can't tell if they're 1's or I's.

[bfordz]

Long week...E177FPf (sorry)

[R_J]

It looks like U851 is a 5 volt buck regulator, pin 1 is the input (12v), pin 2 is the output (5v), It feeds U801 3.3 volt regulator, pin 3 is the input (5v) pin 2 is the output which is low.
I suspect U802 is a 1.8volt regulator so something could be shorted on its output which is also loading down its input.
I suspect the number could be ams1117-18

[CapLeaker]

ah, so there is power to the main filter...
Looks like that U801 is feeding U802 power. So U801 must be bad or getting loaded down.

[bfordz]

I included a better pic of U801 for reference.

For U851 here are the actual v readings:

1 - 12.0vdc
2 - 5.2vdc
3 - 0.0vdc
4 - 1.25vdc
5 - 0.0vdc

sorry for the delay, I was away from my computer this weekend.

[bfordz]

RJ, thank you for your help and input. Also, the regulator lessons and how they function.
It also encouraged me to look a little further to learn some more besides just replacing "caps".

Capleaker, thank you for the 'snubber cap' information, I would have replaced it but then that's why I inquired here first. I actually 'thought' I had something when it tested open. Live and learn!

[CapLeaker]

I’d replace that 3.3v regulator and see what happens.