HP monitor clicking

[budm]

Re: HP monitor clicking

Please take the resistance reading on the B again without the CN701, and also take the DCV reading of A, B, and C.
I wonder what the B is for, it's showing around 300 Ohms compared to A and C.

[Joe Black]

Re: HP monitor clicking

Hmmmm, OK. Here goes: MEASURED WITHOUT CN701

GND and A= 9.57 Kohm

GND and B= 0.310 Kohm

GND and C= 2.77 Kohm

Voltage over suggested points with reference to suggested ground:

A - jumps from 21 to 23V;

B - jumps from 0 to few hundred mV;

C - stays firm at 0.03mV

BOTH WITH AND WITHOUT CN701 CONNECTED.

/rant

I'm just trying to learn here, I figure out you believe some component is shorted to ground, and we're trying to figure out if it's on main or power board, right?

These readings I got would mean it's on power board definitely? And on the line where the B point is located?
Or maybe I'm completely off trail.

[budm]

Re: HP monitor clicking

Clicking is the sign of either too much load for the power supply to handle so it goes into shutdown/restart mode.
I do not expect 21V to be present on this 15" monitor, something is not making sense for me right now.
I also do not expect 'C' to be in mV either but then again I need find out what are feeding A, B, and C.

[Joe Black]

Re: HP monitor clicking

Reading online, I found out that this could be caused by SMPS not having load and therefore being unable to start.

But I can't find what generally should be dummy load, or any explanation of that...

Will do more research when time allows.

[Joe Black]

Re: HP monitor clicking

I wonder what the B is for, it's showing around 300 Ohms compared to A and C.

Turns out that is OK, there is an SMD resistor between that rail and GND labeled 331. I circled that resistor in black.

I did more examining on the power board, and found out this:

The rails circled in red are shorted between them. One goes through big diode, and I traced the other to side pins of the regulator circled in blue. ( I think GND).
However, if I desolder those two corresponding transformator legs, there is no more short between rails, but trafo legs are still shorted.

I don't know if those trafo legs should be shorted, but my guess is NO, which would leave us with a shorted secondary.

[budm]

Re: HP monitor clicking

Transformer DCR will be very very low, it is normal. If the transformer was bad then you will not have any DCV on the secondary side when the main board is not connected to the power supply board.
The part circle in blue is the Common Cathode dual diodes connected in parallel (the two outer pins are connected together), the center pin is Cathode.

[Joe Black]

Re: HP monitor clicking

Hmmm, I understand. Thank you very much for your time and effort, I will abandon this one and focus on others lying around.

[stj]

Re: HP monitor clicking

unless i missed it, you didnt replace the startup capacitor(s) yet.

and check all the diodes in the psu - not just the ones on a heatsink.

[Joe Black]

Re: HP monitor clicking

Checked all diodes already, but not sure on startup caps since I don't know which are those...

And can you guys please tell me what are those on picture...?

[budm]

Re: HP monitor clicking

https://www.badcaps.net/forum/attach...1&d=1467235478
Two small green sleeve electrolytics caps next to each other, one of them is C606.

[Joe Black]

Re: HP monitor clicking

Thanks again, budm. I have checked those with my ESR along with other capacitors; they tested out perfect; both capacitance and ESR rating.

Can you please tell me one more thing: those components I circled in red on that picture; what are they?

[stj]

Re: HP monitor clicking

inductors, ferite blocks with copper wire threaded through them a few times.
they should look like a short on a meter.

[Joe Black]

Re: HP monitor clicking

They do, just never saw them before. Guessed they're inductors based on L markings, but thought I'd better check with you

[Joe Black]

Re: HP monitor clicking

Alright, finally got the time to get back to this.

This short jumper (0 Ohm resistor - circled in black) had a hairline crack along it, and measured as OL. So I removed it and made a blob of solder there-monitor turns on, no clicking.

Now it behaves like this:
-Turns on, squeals a lot, flickers so badly you can't recognize the image.
-Eventually the BL turns off, and as BL turns off, image stabilizes nice and clean w/o BL, visible under flashlight.
-Sometimes it turns on w/o backlight, but squeals the same.

After more inspecting I noticed that I somehow managed to rip of diode circled in red, and lost it.
Are those zeners? Best I can do is take similar one from other board, how different do they get?