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Help with a clamshell iBook -- backlight often won't come on

I used to be on this forum way back in the day (early '00s) under a different username, when I was in high school. Crazy to see that it's still around, and so active!

Anyways, I recently got my first classic Mac in a long time, a clamshell iBook that someone gave me for free as not working. A reinstall of Mac OS 9.2.2 seemed to get things going again, and then I upgraded the hard drive and resoldered a couple of broken connections on the single USB port. Back in Mac heaven, right? Not quite.

Almost every time I boot it now, the display backlight does not come on. It used to work right almost every time, and now it fails almost every time. When it fails, it boots properly, and I can see everything come up super dim. This seems odd to me, as when it works, it works great, with plenty of brightness. Resetting the PRAM (Cmd-Opt-P-R) and resetting the power module with the little pen switch near the power button does not seem to help. The only other symptom I've noticed is that when the backlight does not come on, the computer seems to get hung up for a long time when shutting down (hit power button and hit enter, or select from Special menu).

Any ideas? Does this seem like an issue with the 0.33F supercapacitor, the inverter cable or board, the backlight tube itself, or something else?



Well-known member
It sounds like a power problem (or at least a place to check if you have not already) Are you sure that the power supply is outputting correctly? Maybe check for correct voltage, since the AC adapters from that era are failing as well.


Well-known member
Well, caps should be changed regardless, but that might be very difficult to diagnose whether it is the lamp or the inverter unless you have spares to check against.


Well-known member
I'm yet to see a Clamshell that needed capacitor replacement; I'd suspect the backlight controller to be flaky and/or the CCFL tube = thankfully getting to these is relatively easy with the Clamshell to check.
So I did a little bit of measuring. I couldn't find a pinout for the inverter, but I wound a short piece of bodge wire around the end of each of my multimeter probes and measured the voltage across each pair of pins on the inverter cable where it plugs into the inverter. It looks like pin 2 is ground. Relative to that, pin 1 is at about 24 V, which seems like the voltage that would come from the power adapter. Pin 3 is 0 V at power off, 3.3 V at power on, so I suspect it's the enable pin. Pin 4 seems to be the brightness adjust. After the system has booted, minimum brightness is 0.1-0.2 volts, medium brightness is ~1 V, and full brightness is ~1.8 V.

Seeing as how the voltages to the inverter are sane, and the tube seemed to be in decent shape when things were working earlier, I'm suspecting the inverter, and have ordered a replacement from eBay. Wish me luck.


Active member
I had a similar issue with my pearl white G3 iBook where it turned out that a chip (graphics chip? logic board? I don't remember.) on the main board had come loose. Applying pressure to the lower right of the case from below would re-establish contact. I think it was basically caused by the case being flexible, and people grabbing it with their right hand and carrying it around open, in the process applying pressure to the bottom of the main board about in the middle of the palm rest.

At the time, Apple would replace the mainboard within warranty. But of course the issue came back.

Anyway, might be worth checking if there's a display-relevant component in that area that just needs a bit of solder.
I replaced the inverter; still no luck. Then I bought a little tester on Amazon and verified that the CCFL backlight was good. So I took everything apart and separated the display and the cable to where I could wiggle the cable and watch the backlight cut in and out. Definitely the cable. I've ordered a replacement and am hoping that will fix it.



Well-known member
Nice! They are great little machines for sure. Glad it was relatively simple. Plus, you now have a spare inverter.


Well-known member
Good to see it running properly - inverter cables are made to sustain a high voltage, so it's unusual yours shorted out, did the original inverter look fine? The little LCD tester looks like a good tool to have in the box.