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I have a few old laptops with good LCD panels that I wish to salvage and use as external VGA screen on other computers.

I'am no expert in electronics but I work with computers and know the basics of it. I also did a lot of research on the subject and did my best with no success. I invested some money on parts and really want to finish it but I can't do it without help.

So the LCD panel uses a LVDS interface to connect to the LCD controller board (MT-561B very similar to MT-6820-B).

The LCD panel from Sony Vaio laptop

This is the LCD board. I have some doubts on the red connector (1), the pin layout is printed in the board. I only connected the first ground and the first VCC input, leaving the others not connected. ADJ stands for the brightness adjustments, I'm guessing this is an output to the inverter to reduce the backlight brightness but I'm not sure. I don't really know what BL is but I have read somewhere that is like an on/off pin so I connected it to the 5V.

There is a jumper to choose 5V or 3.3V (4). I'am pretty sure I should use 5v but tried both with no success.

I think I got the LVDS interface cable right because in the pin layout the VCC pins match the red wires in the cable. The keyboard is connected in place as well. (3)

enter image description here

Another thing that I am not 100% sure is the pin mapping for the resolution (2). I want to use 1024x768 (8-1 or 6-1) to test it out, it's not the native resolution but It must be supported right?

LCD controller bottom face with resolution mapping

There was no pin layout for the original LCD inverter so I bought another one, I can't really tell the specifications (can't access Aliexpress) but I'am sure it supports 12V input. Again I just connected the first VCC and GND pins, ADJ was connected to the LCD board and N/F I found out it means like No Function and should be connected to GND.

Inverter front

Inverter back with pin layout

Everything is wired up (and not working) as the following layout:

Pins and wiring layout

I have an ATX power supply from a desktop PC and I use it to get the 12V and 5V that I think I need to use.

My set up

My results so far:

When I turn the power on the LCD panel backlight lights up just a bit, goes off and the keyboard LED keeps on flashing.

If I connect two LCD panels to the LCD inverter both backlights stay on, the keyboard LED flashes too.

This makes me believe that the backlights and inverter are working.

I'm sorry for the long question but I did everything I could and tried to explain it in the best way, now I'm out of moves. What do you think is wrong with the project and what should do next to try to fix it?

Thanks in advance

(I might have connected the 12V on the LCD controller which should get 5V)

EDIT:

enter image description here

The characters on the VGA chip are very small, I could not get a picture and maybe some could be wrong:

Himax Hx6856-A 080LAG 538DNTCC 955710 XM27345

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closed as off-topic by Chris Stratton, Finbarr, Voltage Spike, uint128_t, Harry Svensson Apr 23 '18 at 18:58

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Chris Stratton, Finbarr, Voltage Spike, uint128_t, Harry Svensson
If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ My comment is that you are working way too hard for a second rate solution. The market is filled with a plethora of smaller lower resolution used monitors for very low prices. I am going to guess that you do not go into being a beef farmer for a year just to have a steak for dinner. \$\endgroup\$ – Michael Karas Apr 12 '18 at 3:30
  • \$\begingroup\$ Well I like to recycle old parts :b \$\endgroup\$ – Bruno Tavares Apr 12 '18 at 9:19
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At least the wrong controller...

You've got a lot of problems with the hardware I can see, but at a minimum:

  • Your display is "HD+" which is not supported by your controller. It's barely within the practical capabilities of the analog VGA port you're trying to use.

  • The panel is 3.3V, not 5V, so setting it to 5V may have fried the panel's onboard LVDS controller.

  • The panel from Sharp uses the FFC interface, but the cable in your photo is a pin header type. That means either, you have the wrong cable, or this panel is an OEM-specific version of the standard Sharp panel (quite possible since you removed it from a high volume OEM product). The pin-out of the cable may be non-standard or different from your controller board -- in which case you've either damaged the I/O electronics in the controller chips, or forced the controllers into reset (shutdown).

Some other notes

  • The backlight flash you see at startup is normal and expected. The panel is all white (all pixels open at startup) and then all black (all pixels closed) while it waits for the controller (IIRC for this family of Sharp panels). The backlight is still on, but blocked by the LCD after it's startup procedure. Or... the backlight controller could go into standby after startup by not detecting control signals from the controller (as it's already entered reset -- see above).
  • Post the part number from the controller IC in the middle of your controller board if you want to confirm it's the wrong controller board (but I'm pretty certain it is). Also, post a photo of the other end of the "LVDS" cable (where it's connected to the panel).
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  • \$\begingroup\$ When I bought the LCD controller the seller asked me for the LCD panel label to confirm if the board supported it and give me the apropriate cable. T \$\endgroup\$ – Bruno Tavares Apr 12 '18 at 9:34
  • \$\begingroup\$ I will place the selector on the 3.3V. It crossed my mind that the problem could be what you said, the backlight is going off because the startup sequence is not right. You think the problem is on the LVDS interface, the board pin wiring or the backlight pins wiring? I have posted the info you asked for, thanks for the response! \$\endgroup\$ – Bruno Tavares Apr 12 '18 at 9:43
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As Dr FP said, you may have damaged it for not reading the LCD manual carefully.

Pin No. Symbol Function Remark
1 GND
2 Vcc +3.3V power supply
3 Vcc +3.3V power supply

[Note 2] The shielding case is connected with signal GND.
[Note 3] Please use NC by OPEN or GND. NC terminal is not connected internallly 

( but acts as coplanar shield)

 **    Absolute Maximum Ratings   ** ( may be damaged from heat or other causes)

+3.3V supply voltage Vcc Ta=25℃ 0  ** +4.0 V **

Lamp voltage V La Ta=25℃ - 2000 Vrms 
  • Use native mode 1920 x 1080 2 ( 2 = interlaced), GPU is not fast enough to support non-interlace (1) at high pixels/frame.
    • silkscreen shows jumpers for A13, H13
  • Works perfectly on good 3m VGA cables... been using that for 10 yrs on every system I have including 56" TV. Unless you have ferrite sleeve or SMD CM chokes, VGA may work better than HDMI. If you have PSU noise radiating near HDMI cables, screen will pixelate on content.
  • preload ATX 5V to 5% of rated load for all voltages to be stable. (dummy load or bulb)
  • Check supply voltage with DMM then shut down before connecting and turning on.
  • check all IO signal match controller.
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    \$\begingroup\$ The manual is a nice boost I could not find nothing like it on my research. I had trouble on the jumper settings for resolution. To select the resolution you said should I have a jumper on A and H row and pin number 13? I checked the voltages on the ATX, they are not perfect but are not far from it. I think I understand what you mean with that preload stuff but sounds a bit advanced to me :b do you think it's really worth? Thanks for answering \$\endgroup\$ – Bruno Tavares Apr 12 '18 at 10:07
  • \$\begingroup\$ Follow the documents on the web \$\endgroup\$ – Sunnyskyguy EE75 Apr 12 '18 at 22:39

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