HP monitor clicking

[Joe Black]

Got an HP lcd (older one) that wont start at all, it only clicks every 2 seconds.

With every click, shade of black on screen slighly changes, and that is all monitor does.

no respond to on/off button.

Will post details later, has no visible damage and I have no clue what could it be...

[budm]

Re: HP monitor clicking

It sounds like the power supply detects shorted circuit so it goes into start/shutdown loop, or it may have bad startup cap.
Pictures of the boards?

[Joe Black]

Re: HP monitor clicking

Tested for short, couldn't find any...

Haven't ESR-ed caps yet.

Will take pictures and post, probably tomorrow.

Thanks for suggestions, Bud!

[budm]

Re: HP monitor clicking

BTW, what is the model number of this HP monitor?

[Joe Black]

Re: HP monitor clicking

Heh, can't tell, since it's not at my place...

Will do tomorrow! (Although power+inverter board is BenQ)

[Joe Black]

Re: HP monitor clicking

OK, here goes:

It's an HP 1530. When plugged in makes clicking sound from speakers, and changes shades of black on screen at same time.
ESR-ed all caps, and everything is perfect (even better than expected, many at 0.0x ohm!)

Can't find short anywhere, and V on main cap is stable at 330V as it clicks and loops.

[budm]

Re: HP monitor clicking

The two transistors by each inverter transformer are not shorted? Those Transistors are commonly failed in these BenQ boards, also rectifiers on the heatsinks.
Also look really really close at the transformers and transistors solder joints for bad connections, you can see small rings on the solder joints around the legs.

[Joe Black]

Re: HP monitor clicking

Nope, I'm familiar wih c5707 (5706 here, TBH), and these are all good (tested all legs in between themselves, all are high resistance, no short anywhere)

Also resoldered all power parts and all 3 transformers.

Someone before has added a wire and jumpered FP 751. Jumper is visible on the 2nd picture, right edge of the board. Since I don't know what FP 751 actually protects, I don't know if that's any clue...

[budm]

Re: HP monitor clicking

That FP751 (BELFUSE, 3A) looks to be for the inverter section power supply, this FP751 will usually go bad and has high resistance around 10~15 Ohms instead of going open circuit like most fuse, you can lift one end of the fuse and the jumper to see if the ticking stop.
One end of the FP751 is connected to the bypassed inductor L701.
The pictures of the bottom of the board is not that clear for me to trace the connections.

[budm]

Re: HP monitor clicking

BTW, if you check the resistance between the GND and the Cathode of the D703 (axial body) what do you get? GND and the center legs of each rectifier on the heatsinks what do you get?

[Joe Black]

Re: HP monitor clicking

I removed jumper and fuse, and nothing changed, ticking remained, only screen stopped changing because of the cutted off inverter...

Is it safe to say the problem is in power board?

Cathode of D703 to Ground = 0.306 Kohms

[budm]

Re: HP monitor clicking

I removed jumper and fuse, and nothing changed, ticking remained, only screen stopped changing because of the cutted off inverter...

Is it safe to say the problem is in power board?

Cathode of D703 to Ground = 0.306 Kohms

Yes.

How about the other two rectifiers mounted on the heatsink reading with ref to GND?

[Joe Black]

Re: HP monitor clicking

How about the other two rectifiers mounted on the heatsink reading with ref to GND?

Both center pins = 4.90 Kohms.

Side pins on both rectifiers shorted to ground.

Forgot to mention, Power LED is dead all the time, doesn't even blink.

[budm]

Re: HP monitor clicking

Both center pins = 4.90 Kohms.

Side pins on both rectifiers shorted to ground. That will correct because they are connected together and then connected to the output winding of the transformer which has low DCR.

Forgot to mention, Power LED is dead all the time, doesn't even blink.

So basically there is no low resistance reading on the secondary side of the power supply that will cause ticking.
If yo disconnect main board from the power supply board, is it still ticking?
The power supply is an always on and running power supply so the dcv output should always be present, it does not turn off when the power switch on the front panel is turned off.

[Joe Black]

Re: HP monitor clicking

Indeed, if I unplug main board from power board ticking stops.

Here are the pictures of the main :

[budm]

Re: HP monitor clicking

https://www.badcaps.net/forum/attach...5&d=1466801974
So where does that black connector on the main board top left go to? There is also black connector CN701 on the power supply board, it goes to?
May be you should show us how all the boards are connected together.

[Joe Black]

Re: HP monitor clicking

Of course!
Here goes, so CN 701 go to main board top left, the broad one goes to LCD panel, and the two from the bottom of the pic both go to control panel board.

Ticking stops only when CN 701 is disconnected, if I disconnect either of the control panel cables, it gets quieter, but still ticks.

[budm]

Re: HP monitor clicking

Hmm, I need to find out what the black connector CN701 is for, there are two connectors from the power supply to the main board, the white CN501, and black CN701.
CN701 looks to be for the power connector to run the main board as I can see that there are many big traces to the connector.
I will have to trace them out some how.

[budm]

Re: HP monitor clicking

OK, have the main board and the power supply board connected together, then check the resistance per picture attached, between:
GND and A
GND and B
GND and C
To see what you have.

[Joe Black]

Re: HP monitor clicking

there are two connectors from the power supply to the main board, the white CN501, and black CN701.

I believe only CN701 links power and main board, as both white connectors go down to control panel (board with microswitches and LED);
P501 from power to control board;
and J3 from main to control board.

Measurements as per instructions :

GND and A= 9.57 Kohm

GND and B= 0.297 Kohm

GND and C= 2.07 Kohm

(DMM takes long time to settle on a value, I guess it's normal)