Philips 196V3L monitor power led off

[mikey5791]

Hi, i was given this lcd monitor last week with the issue of power led blinking. Upon checking the power board, i found 2 pieces electrolytic caps bulged and replaced them.
Later, when i switched on ac power and detected 5v and 15v dc at output pins. But as soon as i pressed on the front power button, the led on power button lights for 1 second and it turns off.

So, i tried disconnect the flex ribbon cable from t con board. But all i got is a white screen with nothing on. I suspect there is something short somewhere that prevent the display being turned on. Can someone with experience kindly help to point out and guide how and where to check? I did tried connect a spare led strip as backlight and the it lights up fully and works stable. No blinking or shutting off as per image img2024....3038.
Power board as image img2024...2519.
T con board as image img2024...1429.

[прямо]

If you disconnect the flex ribbon cable, of course you're getting a white screen since only the backlight lights up but the display panel is off.

Why does it matter if the power on led indicator is not working if the monitor can display an image? I have an old Samsung SyncMaster 740N that has the same issue, the power on led indicator goes on and off as it pleases but the display is 100% perfect and operational.

The power on led indicator is controlled by a logic gate on the display main board where your signal input connectors (VGA/DVI/HDMI bla..bla) are located, not on the TCON board of the display panel.

[mikey5791]

Fyi, the monitor does not display any image if i connect the flex ribbon cable and the power led indicator does not light up or turn on. That is the reason i suspect somewhere is shorted as the power led indicator on the front side is not lighted.

[прямо]

Probably 5V on the TCON board is shorted.

Measure the resistance to ground of the 5V pin on the LVDS connector.

Your LVDS pinout depends on the display panel type. There's usually a sticker on it, if you look it up on Panelook.com, you should be able to tell if it's an 8 bit 1ch LVDS or an 8 bit 2ch LVDS.

[mikey5791]

From my DMM resistance set to 2K, red probe on the 5V pin and black probe on ground near CN1 pin on the LVDS connector i got resistance of 0.268

The sticker on display panel says LM185WH2 (T2)(BB) from L&T Display but i couldn't find any info from Panelook.com

Attached image of the LVDS connector.

[прямо]

5V should be the last five pins on the right side of the connector. It's the thick copper plane where VIN test point is.

A 0.2 ohm resistance from that test point to ground is definitely a short (it's the resistance of your probes)

BTW, was the TCON attached to the main board?

Also while you're at it, may wanna check that fuse from VIN to 5V for continuity.

[mikey5791]

Based on your reply, my understanding is the 5v pin should be last five pins on the right side of the connector. By DMM resistance test set to 2k scale, black probe on ground near CN1 and red probe on the 5v pin(as mentioned up here), i got "1" infinite reading. I attached an image of my 5v pin test point as shown by tip of a ball pen. Correct me if i am wrong.
To your question earlier, the TCON was attached to main board.
Fyi, on the right side of connector there is a white color component with "I" marking which i think is a fuse. It has continuity. There is also continuity from the round point label "5V" to the round point label "VIN".

[kasfamily]

Hello, try to send a VGA signal to input ...

[прямо]

Where the ballpoint pen tip is pointing are not the 5V supply pins. As I have already said, the supply pins are on the thick copper plane labeled VIN.

Please don't connect TCON board to mainboard when doing the measurement.

Measure the resistance of VIN test point to ground. Use the multimeter continuity mode.

If confirmed not shorted, then the short is someplace else.

[mikey5791]

By DMM set to continuity mode, TCON board connector disconnected from main board, my black probe on pin 4 ground while red probe on VIN test point, i got reading of 786. If i put my DMM black probe on the furthest right side ground copper plane near the brown sticker, i got reading of 623.

By the way, where else can i check for possible short? Kindly assist.

[прямо]

By DMM set to continuity mode, TCON board connector disconnected from main board, my black probe on pin 4 ground while red probe on VIN test point, i got reading of 786. If i put my DMM black probe on the furthest right side ground copper plane near the brown sticker, i got reading of 623.

By the way, where else can i check for possible short? Kindly assist.

786 what? Ohm?

Problem may not always be a short. It could be anything like a missing voltage.

[mikey5791]

Yes, it is 786 ohms on continuity reading. That means there is resistance. If the reading is "0" zero on my digital multimeter it means complete continuity.,no resistance whatsoever.
I will try to trace why the 5v is missing from TCON board.

[прямо]

Man, I never said the 5V is missing. I said your problem maybe something else other than a short, like a missing voltage.

Even the power supply board could be where the problem is. Just because you connected a led strip, it lighted up and everything appeared to be dandy, only means that the power circuit for backlight is ok.

[mikey5791]

For your info, the 5V is not present at the 5V test point at TCON board. From the power board at the output pins CN902 and doing dc voltage test, i got 5.50v from pins 8,9,10 (+5V). In addition, i got about 30v from pin 4(+15V). I also did voltage test at caps C908 and C907 and the positive side i got 31vdc. Not sure if these readings are normal.

From the main board while doing the voltage test, i got 3.47vdc from pins 5,6,7. The caps at c710 reads 1.88vdc, c702 reads 3.48vdc while both c705&c716 reads 5.51vdc. I found one cap at c433 with zero volt , no voltage whatsoever. It is a 220uf 16v electrolytic cap. I desoldered this cap and measured its capacitance and esr. Its cap is 211uf with 0.07 ohm esr. I guessed this cap is still acceptable.

Then, near the flex ribbon at CN409 and CN408, i tried voltage test and can only detect 3.4vdc at the 3rd circular connector/test point. But this voltage just stops here and doesn't seem to reach to the TCON side. I hope to recover the use of this monitor and not to throw to the rubbish dump and pollute our earth. Anyone know what else i can do or check why is this happening? I am attaching the front and back of the power board and main board for reference. Please ask for more photos or correct me if i am wrong.

[прямо]

Here's a simple guide about TCON and the voltages you will find when it's working properly.

https://www.electronicsrepairmadeasy...tages.html?m=1

There are test points on the TCON board that you can probe to measure those voltages.