no brand monitor wont turn on backlight

[senndogg]

this is a cheapo chinese one.
there is no backlight. the ccfls do not turn on at all.
display is ok with the flashlight test.
voltages seem ok, 13.02V and 4.98V.
from the main board:
ADJ: 5V
EN: 0V. this is not ok, is it?
can i try to bridge a 5V in it?

[selldoor]

Re: no brand monitor wont turn on backlight

Your pictures are exciting but most would prefer a shot looking straight down on the
Powerboard with it all in the one picture. Also one of the backs of the boards. Though I assume you are leaving them connected till you see if you can bridge.
Capxon caps - not great!

[retiredcaps]

Re: no brand monitor wont turn on backlight

1) The note on picture composition is applicable to your post. It shows the exact composition we want.

https://www.badcaps.net/forum/showpo...7&postcount=21

2) If you get no backlight, I would suspect an open fuse (possibly on the backside), or shorted mosfets (again on the backside).

[budm]

Re: no brand monitor wont turn on backlight

The EN on should be High for the Inverter to turn on, do you this pin jumps at all when you trun on the monitor? The ADJ is for backlights dimming control.
I also see surface mounted fuse F1 bythe left white connector of the main/t-con board, is it OK?

[senndogg]

Re: no brand monitor wont turn on backlight

1) excuse me for the photos, it was dark and used flash. couldnt take a straight picture because the flash reflection. anyway today could take some clear ones.
2) the mosfets are not shorted. F1 and F51 ok.
3)the EN does NOT get any value, even when first attached to the mains.

i suspect a problem in the main board. dont you? but i am a little confident in repairing it since there is also the tcon there, playing with it can result fatal for the display, or it is just my impression.

[senndogg]

Re: no brand monitor wont turn on backlight

Sth has gone wrong and today the monitor wont turn on. the led turns green for 4 seconds, then goes red. cant read anything on the display with a flash. the signal cable is always connected. i am gonna check the 5V rail caps.

[senndogg]

Re: no brand monitor wont turn on backlight

caps changed. monitor half gone. only the led lights.
there is 3.3V at the regulator pins.

[selldoor]

Re: no brand monitor wont turn on backlight

Hi I am strugging to follow this (not Unusual) Is the 5v still there?
Can you just recap on the current position. Voltages on CN1 when connected and when not connected. Which regulator has 3.3v.
Is the EN Pin and connector clean? Following the EN1 Trace where does it go
Looks like under RJ51 then where?. Can you test for continuity from the back of the conector on the mainboard to where it goes.

[senndogg]

Re: no brand monitor wont turn on backlight

yes selldoor. there is a stable 5V.
in the CN1 the backlight ADJ is not 4.9V any more when disconnected. the EN1 still 0V obviously. disconnected only the EN and attached the connector, still 0V from the main board even during powering on and off the monitor. but i have to say that this is not a backlight problem any more, there is nothing in the display and the led turns red (like you have connected the signal cable to a shut pc) even when the pc shows the desktop at low resolution.
the 3.3V comes from U3 and U4. meanwhile 2.5V comes from the U2.
i traced the EN (connector and pin clean) in the main board, and it goes like this:
to the middle pin of transistor Q5. one pin of Q5 is grounded and the other (0.68V) goes to resistor R5. then (at this point 2.7V) goes to the main chip U9.
now it looks a bit complicated since it involves the big chip, but this is what i want to know. if is anything shorted or opened (resistor, diode etc) or should i give up cos the chip may be fried.

[senndogg]

Re: no brand monitor wont turn on backlight

this is a simplified schematic of the EN route in the main board.

[senndogg]

Re: no brand monitor wont turn on backlight

maybe Q5 shorted?