HP Z27s, cycling backlight off for half second, on for 5

[clements84]

I have an older HP Z27s Display here that turns on ok from cold and works for a couple minutes, it then shuts off the backlight for about half, then back on for about 5 seconds, then repeats in a never ending cycle.
Thermal imaging points to an IC on power supply, however I cannot find any information online from the markings. (see last photo)
Note, during the time the backlight shuts off, the rectifier output jumps from its constant 105vdc to approx 160vdc (maybe normal because of the loss of load?)

Any further troubleshooting suggestions or IC information?

[lotas]

Re: HP Z27s, cycling backlight off for half second, on for 5

It should warm up, because this is a Led driver, you rather have poor soldering (ring cracks) and because of this, contact disappears, solder suspicious places well.

[CapLeaker]

Re: HP Z27s, cycling backlight off for half second, on for 5

Turn the backlights away down like less than 50% and see if they stay on longer.

[harp]

Re: HP Z27s, cycling backlight off for half second, on for 5

What is voltage on conector wires
black-red
black-green
black-white
during test, are they fluctuated with backlight?
Can you take a pictures of control board?

[clements84]

Re: HP Z27s, cycling backlight off for half second, on for 5

just to point out the fluke IR pic is in Celsius

and to answer the questions, the solder does look bad in those pics, but are great in person

The monitor does work with the brightness lowered. The timing between the cut off shortens as the brightness increases.

also when the monitor was cutting out (turning backlights on/off) I hit the back part of the board with cold and the monitor worked properly for a minute or two again until it heated back up again.

[clements84]

Re: HP Z27s, cycling backlight off for half second, on for 5

There is two red wires to the lamps tied to same point, so I used those as reference point. The readings on each line are:
Green 65.8v
Yellow 66.1v
Brown 65.7v
Black 72.1v

I removed each of those 4 pins to take current reading and they are
Green 120.2mA
Yellow 120.5mA
Brown 121.2mA
Black 122.3mA

[harp]

Re: HP Z27s, cycling backlight off for half second, on for 5

I am a little confused - I mean a wires of the first photo (I guess there are for control board, with inputs and driver for display, not wires at last picture. But never mind... if you see that you can control that behaveour, just focus on particular area, the exactly components.
I had a simmilar problem, and shurely pinpoint a bad electrolite with corner of ice cube. It was on control board this time.

https://www.youtube.com/watch?v=aPAeZWeJ-nw

You can tested C816 or one closer to hot chip also, with ice cube or to speedup determination, with hot air at lowest temp after cold.

[JohenClark]

Hi. Does anyone have the schematic diagram for the power board of the HP z27 s monitor? My monitor had the issue with the flickering lines at the bottom bezels and a bit of overheating then a few days back it just shut down and there was a smell of smoke in the air. On disassembling the monitor I found that one of the resistors had caught fire and the fuse had blown. The resistor leads to a 16-pin SMD chip that is not legible so I can't pull up its datasheet. Can anyone help me identify this chip and its datasheet so I can troubleshoot what could have caused this? I have marked the location of the chip and the resistor that blew in the attached picture.