180 Backlight

[christie]

Hi all,

Have a new-to-me PowerBook 180.

Working fine, screen's great... until now.

The backlight comes on at boot, stays on when the mouse pointer appears and sometime around happy Mac and the 7.1 Welcome to Macintosh the backlight goes off.

Lcd is fine, just no backlight.

Where do I start tracking this down? Seems weird that the backlight comes on, string and bright and then goes down during boot..

Thanks!

 

[bibilit]

Inverter board maybe ?

 

[christie]

Yeah, I was thinking that too.

I repeated booting it a bunch of times. Several times the backlight stayed on fine. Several times it didn't. The timing of when it went down wasn't always consistent with what the action on the screen was. It was consistent, however with when the hard drive started spinning up. I find this curious.

I wonder if it is possible that the hard drive is starting to go south, and when a lot of current is needed to get it going, it tanks the power needed to keep the backlight on? 

Anyone think this is possible?

 

[Ferrix97]

Have you tried cleaning the slider control? IIRC on some models is software controller so if it's defective it will start misbehaving only in the boot process

 

[christie]

That's interesting. I will try that when I have it open. I did play with booting it with the slider set to different positions, and with different prefs set for dimming, thinking something software-wise was borking it, since it's fine before some point during boot.

 

[Ferrix97]

Try booting from something like the NAD or Utility disk, they usually don't have PowerBook support therefore they won't software control the backlight. 

 

[bibilit]

Two tiny capacitors on the inverter, not sure about the 180, but the 140/170 range has those for sure.

 

[Rajel]

Two tiny capacitors on the inverter, not sure about the 180, but the 140/170 range has those for sure.

The 180 should have them, similar to the 160.

 

[christie]

So for the last two days, it has been functioning fine - normal backlight behavior. I have no idea why it started acting up and therefore no idea why it's fine.

Thanks to all who contributed suggestions.

 

[techknight]

Do you know for a fact your power brick is good? Because I do know those things are starting to leak now, as discovered by others here. 

 

[christie]

No, I do not.

Made a preliminary attempt to crack the brick open to recap it but so far it's resisting my efforts.

I switched to a recent 7.5v 2A supply until I can get that one (or another) open.

 

[Rajel]

Do you know for a fact your power brick is good? Because I do know those things are starting to leak now, as discovered by others here. 

I do need to crack mine open and check, but metered out it was stable. Should throw a scope on the output of my brick and see what the noise is like.