2400c Intermittent Backlight

[LCARS]

On my quest to fix all the Macs on my list, I've come to my two 2400c PowerBooks with the same issue, intermittent backlight. Every other cold boot or wake from sleep results in the display functioning (with direct light I can see the display) but without backlight. I've run through all the prescribed resets to no avail. I have not encountered the GLOD (green light of death) from the sleep indicator. Aside from this backlight issue, they run normally. When it does come on, its bright without any unusual buzzing or humming.

This happens on battery power (those Japanese cells still provide 40 minutes of power) as well as on AC and AC w/o battery. To the more knowledgeable, does this sound capacitor related? I am considering sending them in to be recapped but as this model is notoriously difficult to open up, I'm open to suggestions.

 

[jeremywork]

I might try unplugging the PRAM batteries. In some cases when the main battery dies, and the PRAM battery is low but not dead, the PMU can freeze and remain powered on in the frozen state, which can mean some devices do not operate at startup. Removing all sources of power for a minute and then plugging in AC power is a good way to be sure the PMU is not in a frozen state.

 

[LCARS]

Ah! Thank you, Jeremy. Now that you mention it, it does act odd when powered for the first time in a while. It will boot instantly when power is supplied (battery or AC) without pressing the power button. The PRAM battery is in a tough spot to get to. Do you know if this is a machine that requires its presence to power on?

 

[Byrd]

The 2400c does not need a PRAM battery to power on, nor should the absence of one introduce any quirks.

I recently rebuilt 3 x 2400c, all had dead PRAM batteries - one had leaked while the other two appears OK but the battery connector on the motherboard was green/corroded.

 

[jeremywork]

It will boot instantly when power is supplied (battery or AC) without pressing the power button.

I find this normal for PowerBooks, and many (all?) later Intel 'Books too. It will operate fine with a good battery or with no battery; just want to be sure there isn't a half-dead battery keeping a super-low voltage applied.

 

[LCARS]

A half-dead battery is probably what the PRAM batt. has become in both machines. Thank you for your help. I'll be able to get it out next weekend and I'll post how it goes.