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Model A1224 / Mid 2007 and Early 2008 / 2, 2.4, or 2.66 GHz Core 2 Duo processor

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Backlight on for 200-300ms @ boot & stays off - otherwise 100% working

The backlight turns on for roughly 200-300ms when the computer first powers on but then turns off and never comes back on. The computer is 100% fully working otherwise. It has an image on the display and everything else is tested and works.

I have already tried replacing the PSU and inverter board, but there’s no change.

PSU output measures normal.

Inverter input does not measure normal.

The inverter board has 4 pins on the connector: V-in, ground, PWM, and Enable. V-in is the proper 12V, ground is obviously 0v, Enable is 3.3V , and PWM *should* be 3.3V but I am only measuring 1V. I inspected and measured the appropriate components on the board and they measure according to the schematic.

I found a similar question posted by another user with similar board experience who also did the same testing as I have, but a new PSU fixed his problem whereas it did not for mine.

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@dpwhitty

there seems to be a lot of dancing around on this question. To clarify, you replaced both the power board and the inverter with known-good replacement boards. If so, then the only next option will be to check the panel itself. Common panels for this model was a Phillips (LG) LM201WE3-(TL)(F5) You need to check yours and let us know what your panel number is. VLCD for the common panel should be 5V. This type of panel requires two power inputs. One is to power the LCD electronics and to drive the TFT array and liquid crystal. The second input power for the CCFL, is typically generated by an inverter.

Failed CCFL’s often display this behavior “the backlight will come on for that split second before it cuts out. “ but since they are only for the backlight, you should still see the image by shining a flashlight at an angle against the screen. New power board and inverter would then indicate a faulty driver board (part of the panel)

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The internal display does put an image out on the screen as I stated at the end of the very first paragraph in my original post.

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Corrected that answer by removing the sentence about the voltage to the TFT since your panel receives it. Still, the issue will obviously not be with your new power board or the new inverter, but you will still have to look toward the panel. What 820-xxxx is your logic board? Have you given any consideration to temporarily supplying the needed voltage to the PWM to see if that changes anything?

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It's an 820-2223. I have tried supplying 3v3 to PWM with no luck. I'm fairly confident the issue is with the CCFLs, I just need a solid second opinion before I get my shop to order the parts after 2 purchases & returns already.

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@dpwhitty you are really at a crosspoint. If all your voltages are checking out I would lastly try to get a datasheet for the panel and verify the signals on the panel itself. After that I'd go with replacing the CCFL's and re-evalaute. If nothing else it would at least rule those out.

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Given the age of the system I would replace the PRAM battery iMac Intel 20" EMC 2133 and 2210 PRAM Battery Replacement as sometimes the settings get lost or corrupted when the battery is low or dead.

A failed Inverter could be your issue. Both the power supply and the invert work hand in hand to supply the needed power to drive the CCFL’s for the backlight to work iMac Intel 20" EMC 2133 and 2210 Inverter Replacement and the needed part iMac Intel 20" EMC 2210 & 2133 Backlight Inverter.

To verify shine a flashlight into the screen at a sharp angle you should see the faint image of your desktop and its icons. If you do then the issue is within the backlight logic and/or the CCFL lamps.

If you’re careful you should be able to measure the voltage going to the lamps (be very careful! This is high voltage).

iMac Intel 20" EMC 2210 & 2133 Backlight Inverter图片

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iMac Intel 20" EMC 2210 & 2133 Backlight Inverter

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iMac Intel 20" EMC 2133 and 2210 PRAM Battery图片

指南

iMac Intel 20" EMC 2133 and 2210 PRAM Battery Replacement

难度:

简单

5 - 10 minutes

iMac Intel 20" EMC 2133 and 2210 Inverter图片

指南

iMac Intel 20" EMC 2133 and 2210 Inverter Replacement

难度:

中等

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I've already done replacements with the PSU and inverter board with no change in the backlight and the machine does as an image as stated. The PRAM battery is good at 3.08V, I just measured it to confirm.

When I try to measure the output to the CCFLs my meter picks up what looks to be around 120-130V (I'm not sure how accurate that is, it doesn't stay on long enough for my meter to measure) before it drops to 0V.

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I wasn't sure if the image you saw was on the internal or an external display as you hadn't made that clear.

Did you replace the PRAM battery yet?

As the voltage is present then disappears the issue is still within either the power supply or the inverter.

But! First replace the PRAM battery and reset the settings to make sure you're not chasing your tail here. If the setting is not holding this could explain things.

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Ah yes it is with the internal display.

I just replaced the battery & reset the PRAM, but no change.

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I also just noticed that if I put it to sleep and then wake it, the backlight will come on for that split second before it cuts out.

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OK, I had one more thought! Lets make sure the thermal sensor on the LCD is not messing us up. Using an external display (so you can see things) install a sensor monitoring app like TG Pro. Depending on the OS release you have on the system you may need to contact them for the older version.

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Daniel W 将永远感激不已
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