No Backlight unless I short LCD driver plug

Saw this on another site - the pinouts match my A1211 Macbook Pro inverter feed plus.

http://www.techsupportforum.com/forums/f...

Re: Dead LCD Backlight on Mac Powerbook G4 Aluminum 17"

This problem is solved... sort of. The bottom line was that the logic board was NOT outputting any voltage for the "dim control" input to the Inverter board. According to some other info found on the Internet, the "dim control" pin should have a voltage ranging from 0 to +4 volts depending on the dimming desired (where 0V = no light, 4V = max light). Since the logic board wasn't outputting any voltage on that pin, the backlight remained off. So, since I had no intention of buying a new logic board for such an old computer, I decided to just manually put +4V on the pin. Here's how I did it...

First off, the CORRECT pin names and voltages to the input connector of the Inverter board are here (again, this is for Powerbook G4 17" Aluminum). This is slightly different than what I wrote in my original message...

CHASSIS GROUND - Green wire (connector pin 1): Hardwired to chassis ground

+12V SUPPLY - Black wire (connector pin 2): +12V

CABLE GROUND - Gray wire (connector pin 3): 0V

+5V SUPPLY - Blue wire (connector pin 4): +5V

DIM CONTROL/ENABLE - Silver wire (connector pin 5): 0 to +4V depending on dimming

So, it was the DIM CONTROL that was dead from the logic board. I had both 12v and 5v available to me at the input connector to the Inverter board so, my first thought was to just connect the 5v to DIM CONTROL. At first it worked but, after about 1 minute, the backlight would shut off, presumably because the Inverter was being "overdriven" and it has some kind of overcurrent shutdown circuitry. So, I went to plan B and, though experimentation, found that a 3K ohm resistor placed between pin 4 and pin 5 brought the voltage on the DIM CONTROL to +3.8V which kept the backlight bright without it shutting down. See pictures below.

Now, for the bad news. Not only will the screen not dim (which I can live with), but it also won't shutoff when going into sleep mode (the display goes away, but the backlight remains lit). For the record, it DOES shutoff when the computer is ShutDown. But, this poses yet another challenge. Since I generally only use my computer from home while it is plugged in, I may not worry about this one for now. But, for many people, this might be a showstopper. None the less, I did get the backlight working.

John

What I did was take a lamp from another broken laptop I had and used it as a tester to see if the inverter was okay.

That did it for me - you can not test the inverter output with a digital meter.

Hi, Repair Pros!

I understand that this thread is old, but still, worth a try.

I have finally disassembled my Macbook Pro A1211 and fixed "couple" of things:

1. Made my DVD work - was dead - probably distorted after fall, ended up leaving one screw out - and it worked.

2. Cleaned the air ducts and replaced the thermal paste on three chips - now normal temperatures are <50deg C, while they were >80deg C ever since I bought it new.

3. Removed the cover - so that I see the screen with ambient Backlight :) - for the situations when external monitor is not enough. :)

I would like to say big thank you to ifixid - without you - all that would be impossible. Now, I come to the question..

I had my backlight come off and then on several times, but once, it made some smoke and smell, and went off for good.

I do not have any replacement parts yet, but that's what I found so far:

The pins going to inverter:

• Dimming control works fine, ranges from 0.6V to 3.2V when adjusted.
• 12V is fine
• 5V is missing. Got 1.3V instead directly from the board, so cable should not be an issue. I tested it with inverter board disconnected.

So, my question is - can someone say if I should measure 5V even with Inverter board disconnected?

If yes - then where should I look for defects?

Is there any fuse that could have been killed with dead inverter board?

Other than dead backlight - laptop seems to be fully functional.

The smoke was coming from the left part - in the area of speaker, as far as I remember - well, it's couple of months back.

Hi,

I did test the output as described elsewhere with the high frequency Hz detection. There's no output, but I guess it can be because the inverter is dead or because the power input voltage is too low.

But my question is rather about the power to the inverter, i.e. that lower than 5V value. Anyone has ideas why it might be and how to troubleshoot it?

Thanks!