HP no backlight

[davg]

This is a 19 " HP which powers on OK but the backlights will not light. I tested these lights and they test OK I replaced all the cap on the power board with same results. I am looking at retiredcaps sticky and am thinking that it may be a transistor but I am rather intimidated by these because I am not sure how to identify them for example how can one determine the start/stop transistor? The signalling transistors? etc. This board has quite a number components with the Q designation but look different. Some has E,C,B and some has S,G,D and than there are some with 8 contacts like the 2 (P607 BD5A18)

[retiredcaps]

Re: HP no backlight

(P607 BD5A18)

P607 datasheet

http://pdf1.alldatasheet.com/datashe...D/AOP607L.html

Measure to see if S1-G1, S1-D1 and D1-G1 are shorted. Do the same for the "2s" and report your readings.

[davg]

Re: HP no backlight

Thanks retiredcaps assuming pin 1 is indicated with a dimple the readings are as follows
Q 104
S1-G1-30 m ohms
S1- D1- 4 M Ohms
G1-D1- 0L
S2-G2-69 M OHMS
S2-D2-0L
G2-D2-0L
Q105
S1-G1-29 M Ohm
S1-D1- 20 M Ohm
G1-D1- 0L
S2-G2-38 M Ohm
S2- D2-0L
G2-D2-0L
where I get a reading the reading is continually decreasing?

[retiredcaps]

Re: HP no backlight

None of those mosfets are shorted.

On the connector to the main/logic board (which is cut off in the picture), is there a legend? If yes, is there a pin that says BL_ON or something. The main board generates the BL_ON and it should be > 2.0V DC.

[davg]

Re: HP no backlight

Yes there is as follows BRL ON_OFF, +5 volts, +5 volts, GND, GND, GND, +12 Volts. The voltages on these pins read 1.57v, 0v, 5.22v, 5.22v, 0v, 0v, 0v, 12.24v. You say non of these mosfets are shorted!! what kind of readings would I get if they were? (just learning)

[budm]

Re: HP no backlight

What is the model number of this HP? Can you zoom out a little bit so I can see the whole board, both sides? By the way, do you see the lights even flash on at all?

[retiredcaps]

Re: HP no backlight

Yes there is as follows BRL ON_OFF, +5 volts, +5 volts, GND, GND, GND, +12 Volts. The voltages on these pins read 1.57v, 0v, 5.22v, 5.22v, 0v, 0v, 0v, 12.24v. You say non of these mosfets are shorted!! what kind of readings would I get if they were? (just learning)

BRL = 1.57V
ON_OFF = 0V

I'm not 100% sure if BRL is backlight. The "R" is confusing me. Additionally, ON_OFF could be the backlight on/off command.

I define a short as anything less than 30 ohms. AFAIK, there is no industry agreed upon value.

[davg]

Re: HP no backlight

The model # is HP-VS17 I will upload pictures in the morning. I have it apart now but I can't be sure if it flashes or not but if it does its quicker than the eye. When plugged in the blue power light comes on than goes to amber. I don;t see any flash of the backlights but I can see the image with a bright light.

[davg]

Re: HP no backlight

BRL = 1.57V
ON_OFF = 0V

I'm not 100% sure if BRL is backlight. The "R" is confusing me. Additionally, ON_OFF could be the backlight on/off command.

I define a short as anything less than 30 ohms. AFAIK, there is no industry agreed upon value.

On closer look that BRL is actually BRI ON_OFF if that makes any sense??. So is that 1.57v within tolerances for the ON pin? Is the 0V correct for the OFF pin? All others seem OK

[retiredcaps]

Re: HP no backlight

BRI is brightness. ON_OFF, then, is your backlight on/off. It is 0V, then the main/logic board is not generating it.

Check the voltage regulators on the main/logic board. My sig file has a how to guide.

[retiredcaps]

Re: HP no backlight

Post a picture of the main board as well.

[budm]

Re: HP no backlight

Since the LED is AMBER, then that make sense why the ON_OFF is 0V. If the main board does not sense the video signal from the PC, it will turn off the inverter and the power to the LCD T-CON board. So check the regulators on the main board as suggested by retiredcaps.

[retiredcaps]

Re: HP no backlight

If the main board does not sense the video signal from the PC, it will turn off the inverter and the power to the LCD T-CON board.

Connecting a working source (PC) to the lcd monitor is always recommended.

[davg]

Re: HP no backlight

Here are the pictures that budm requested and with the unit attached to a pc the blue light stays blue but there is no flash of the backlights at all. I am hearing a humming sound on the power board when everything is hooked up. Is this normal? I have to do some reading before I start testing the regulators.

[davg]

Re: HP no backlight

The readings on the two regulators I304 and I305 are as follows:
I304
AIC line 1
1084-33PM line 2
328GC line 3
pin #1- 0V
pin#2- 3.29v
pin#3- 4.9v

I305
1117 line#1
-18PE line#2
91OCT line#3
pin #1 - 0v
pin#2 - 1.79v
pin#3 - 3.29
pins numbered left to right with long pad north

[davg]

Re: HP no backlight

I noticed that the caps on this board are CapXon even though they look OK could these cause the problem?

[jetadm123]

Re: HP no backlight

Your voltage regulator readings look good. Here's what I think the problem is:

On your photo of the logic board, what is the part number for I308? It's the 3 terminal device right above the 10-wire wiring harness. If it's something like MAX809/810, then it's a reset controller. If yes, with power off, use your soldering iron to lift the VCC and RESET pins off the circuit board. Power up the monitor to see if you get an image. Note: failure of this controller has caused the same problem on various acer models.

[davg]

Re: HP no backlight

Thanks jetadm123 The best I can tell the markings on that I308 is ARNQ4 but it is so small it's a job to tell.?

[budm]

Re: HP no backlight

So when the LED turns blue with connection to running PC, do you now get >3VDC at the ON/OFF PIN? If you do, then we need to go back and troubleshoot the inverter circuits.

[davg]

Re: HP no backlight

Thanks budm when connected to running pc I am reading 2.32v 3.24v 5.12v 5.13v 0v 0v 0v 12.24v on that 8 pin connector marked BRI ON-OFF, 5V, 5V, GRN, GRN, GRN, 12V. When the light turns amber the 3.24v drops to 0v?