HP W2408 No Power

[kjspylite]

Hi everyone. I've used forums to fix many things because people like you are willing to help people like me. However, I've never fixed anything like this. In other words, I'm a total noob. Hope someone can help me.

Monitor: HP W2408 24" LCD

Symptoms: No Power, No stand-by light, absolutely no response when plugged in and the power button pressed.

I hope my pictures were correctly inserted and they are usable.

I have a DMM and am somewhat competent with it.

Can someone point me in the right direction?

[budm]

Re: HP W2408 No Power

I will assume that you have already check the Main AC fuse (the little red round component by the AC inlet).
Next, check to see if you do have 165~170Vdc on that large round main DC filter cap, no need to turn the monitor on. Be careful since you will be working on the AC primary side, do not touch anything with your body parts.

[kjspylite]

Re: HP W2408 No Power

The fuse (F850) is a closed circuit. Ohm reading was 28. The large round cap (C854) jumped between 175 and 195Vdc.

[budm]

Re: HP W2408 No Power

OK, you do have voltage on the primary side.
Do you have any DC voltage on the two connectors (one red/black wires, and another one with multi color wires)?

[kjspylite]

Re: HP W2408 No Power

What is the procedure for checking these connectors?
Do they need to be pluggedinto the other boards?

[retiredcaps]

Re: HP W2408 No Power

Ohm reading was 28. The large round cap (C854) jumped between 175 and 195Vdc.

1) I'm suprised that the fuse is good with a reading of 28 ohms. Do you mean 0.28 or even 2.8 ohms?

2) A fluctuating voltage on the large cap, C854, is never a good sign. It should be 175V DC steady, not 195V DC.

3) One thing that could explain these readings above is that your multimeter has a weak battery or your probes are fraying internally.

4) For one retiredcaps' bonus point, post a picture of multimeter.

5) Those are excellent clear focused photos.

[retiredcaps]

Re: HP W2408 No Power

What is the procedure for checking these connectors?
Do they need to be pluggedinto the other boards?

1) Plug in all your boards.

2) The colored connector on the power board seems to be the one connected to the main board. If yes, put your black probe on a main board ground screw and your red probe on each colored connector. Report all your readings like so

pin 1 = 5.0V
pin 2 = 0.0V

3) U117 and U102 are voltage regulators on the main board. Excellent clear focused pictures lets regulars use the actual pcb designation rather than downloading the pic, marking it up in paint, and reposting it.

4) Set your multimeter (if manual range) to 20V DC.

5) Put your black probe on a ground screw. Leave it there the entire time. This is your ground.

6) Put your red probe on each of the pins including the "cut" pin, but ignore the "fat" tab.

7) You should have 3 readings per regulator.

8) Report them like so along with the part number of the IC.

U117
AS1117-33
pin 1 = 0.0
pin 2 = 3.3
pin 3 = 5.0

[kjspylite]

Re: HP W2408 No Power

Wow! I think your right. I tested a 60 amp fuse known to be good and it failed. Now it wont read the fuse from the monitor. unfortunately, i dont have a 9v laying around so i cant continue tonight. I'll put a new battery in and will repost my readings. Thanks for your time, guys. Cause you asked, I posted a pic of my DMM. Its nothing special, but I assume its good enough to do the job.

[budm]

Re: HP W2408 No Power

Wow retiredcaps, it looks like I need to ASK people to check and make sure their meter is working properly first from now on.

[kjspylite]

Re: HP W2408 No Power

Sorry, budm. I really appreciate your help. I am new to this and rarely use my multimeter. I'll get it corrected and will start from the beginning and post my findings.

.....If you need any help diagnosing a carburated outboard motor, I can return the favor and help you with that!

[budm]

Re: HP W2408 No Power

No problem.

[momaka]

Re: HP W2408 No Power

The large round cap (C854) jumped between 175 and 195Vdc.

That's might be a problem there. This circuit has PFC so the voltage across C854 should be much bigger. For most PFC circuits it's 350V+, usually in the 370-380V range.

If the voltages on the output of the power supply are fluctuating, then the start-up cap might be bad. For your power supply, the start-up capacitor is likely C872 (a small electrolytic capacitor next to that big primary cap). The problem could also be caused by C884 (another small electrolytic cap), which provides the PFC/PWM controller with power once the power supply has started.

Also check D858 (mounted on the heat sink) for short circuit, with the power disconnected, of course.

If D858 is good, try replacing both C872 and C884.

*EDIT*
Since you were having trouble with your multimeter, first get that taken care of and then re-check the voltage across C854. If it's still jumping, then check the items I mentioned above.

[retiredcaps]

Re: HP W2408 No Power

unfortunately, i dont have a 9v laying around so i cant continue tonight.

I put new 9V batteries in my smoke detectors and use the "old" ones in my multimeters. The "old" ones have enough voltage to run the multimeter and generally are only 6 to 12 months old.

PS. One retiredcaps' point for a picture of the Craftsman.

[budm]

Re: HP W2408 No Power

I think that voltage reading on the cap I have him check is when the monitor is plugged in but not turn on yet.

[retiredcaps]

Re: HP W2408 No Power

Wow retiredcaps, it looks like I need to ASK people to check and make sure their meter is working properly first from now on.

When I saw a "good" fuse measure 28 ohms, I knew something was wrong.

[budm]

Re: HP W2408 No Power

I was assuming .28 Ohm, did not think his meter will be off that bad.

[kjspylite]

Re: HP W2408 No Power

Ok. I have a reliable DMM that I borrowed from my father in law. I attached a pic just for retiredcaps. Im went through everything above and will post them in next (from my desktop pc, im currently on a tablet).

[kjspylite]

Re: HP W2408 No Power

F850
0.2 Ohm

C854
175-195 Vdc fluctuating

CN851 (black and one red wire connector going to video board)
pin1 0.0
pin2 0.0
pin3 2.1
pin4 0.0
pin5 0.0
pin6 0.0
pin7 0.004
pin8 0.0
pin9 0.0
pin10 0.0
pin11 .26
pin12 .26
pin13 .26
pin14 .26

CN852 (multi colored connector going to back light board(?))
pin1 0.0
pin2 0.0
pin3 0.0
pin4 .26
pin5 0.0
pin6 0.0
pin7 2.1
pin8 2.1

U102
1084-33
pin1 0.0
pin2 0.011
pin3 2.5

U117
AS117L-33
pin1 0.0
pin2 0.0
pin3 0.0

The following was in response to momaka:

C872
10-15 Vdc fluctuating

C884
0.2-1 Vdc


Hope this makes sense to someone...

[retiredcaps]

Re: HP W2408 No Power

Ok. I have a reliable DMM that I borrowed from my father in law.

Fluke 177 gets another retiredcaps' bonus point (2 and counting). The yellow holster could use a good cleaning with some gojo or fast orange. All my multimeters are purchased used and look brand new when I clean them up. I got some gojo at Wal-Mart for $4, I think and it will last me a lifetime.

http://www.youtube.com/watch?v=02OTFNoB2y0

You might score some needed brownie points if you returned his multimeter looking new. You don't have to take it apart like the above video. I just rub a LITTLE bit onto my thumb and then onto the case. Don't goop it on like the guy in the video.

Also, when the battery gets low on this multimeter, it will show "batt" and not let you take any false readings.

[retiredcaps]

Re: HP W2408 No Power

F850
0.2 Ohm

F850 is definitely good at 0.2 ohms.

C854
175-195 Vdc fluctuating

Not good.

The following was in response to momaka:

C872
10-15 Vdc fluctuating

C884
0.2-1 Vdc

C872 may be your startup cap. If it is fluctuating, it could be bad. These smaller caps don't have to bloat in order to be bad. My guess is that C872 is 47uF 50V.

Replace it with something like a Panasonic FC series and let's see if that is root cause or not.

http://www.digikey.com/product-detai...0321-ND/266330

If replacing this single cap works, most here would recommend you recap the entire power board with quality low ESR caps for longevity and reliability.