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PowerBook Duo 270c - burning power supply


Well-known member

I got a very pretty PB Duo 270c today. 

Everything works fine and so I started to check and format its hard disk using a SCSI-connection with my PowerBook 540c. 

Hard disk seemed ok and so I started copying install files and more from 540c to Duo 270c. 

Suddly I noticed brown smoke from the Duo power supply and so I immediately plugged it out and the smoke stopped. 

After that I used a known good universal power supply and I could continue to copy files. 

Everything seemed ok again but now there is something wrong with the backlight of the PowerBook Duo:

When it starts I have to make it's display lighter each time, as I know this with passive matrix displays, when the PRAM battery is dead. Didn't know this with active matrix displays. 

And then, when the PowerBook Duo is ready with booting, the backlight gets black in several steps (!) after a few seconds. 

This is repeating after every booting up. 

I can see the desktop with a pocket lamp. 

So the backlight seems to be partly dead. 

Could a (now) dead PRAM battery also be the reason of this?

Please tell me your thoughts about this. 




Well-known member
New infos:

PRAM battery disconnected: nothing changes. 

When I let the Duo sit without power for a while, the light screen lasts for a view minutes, so I can see the booted desktop for 1 minute or so. Then it gets dark again.

When I put in the main battery, the PB shuts off itself immediately. 

This is a new fact after the burning issue. 

I got the Duo with the main battery inside and had no problems with it before the burning. 



Well-known member
Next update:

When I let the Duo sit for about 20-30 min without any power it seems to recover itself:

after power on the backlight comes normally, but disappears until I hold down the 

[SIZE=11pt]brightness control button [/SIZE](up) and let it pressed all the time, the backlight comes back and stays normally as long as I (like to) press the "up" button. When I release the button, the backlight dimms down in several fast steps until the desktop is only visible with my pocket lamp again. 

From this moment on I can't get the backlight coming back again - pressing the "up" button does not help anymore. 

Nevertheless I can repeat this power off for several minutes / power on / press button [SIZE=12pt]procedure as often as I like.[/SIZE]

[SIZE=12pt]Is the actuator board responsible for this story? [/SIZE]



Well-known member
It seems like the actual brightness switch is at fault - a closed short forcing the brightness down unless you hold it?  I'd try cleaning the switches next.

Re: PRAM settings, things like screen brightness are also held in PRAM so if your PRAM isn't good it won't save the settings.



Well-known member
Thanks, I'll try cleaning. 

In the meantime the Duo was sitting 2-3 hours without power and when I powered it on again, the display didn't go to sleep for about 20-30 mins without pressing anything. 

The fact is: the Duo was ok for several hours when I got it until the the power supply began to smoke. 

I suppose that a bad capacitor was the reason for this - will see it when I crack open the power supply. 

I will post a picture then. 

At this moment the Duo could have gotten too much power and something inside the Duo could have been damaged. The main battery also was unusable from this time on and had to be removed. 

The question is, what part of the Duo was affected. 

In the developer notes


there is a description how the power management works in the Duo 270c. 

Maybe I'll find the solution there. 

Last edited by a moderator:


Well-known member
Problem solved! :)

After waiting more than a week - PB Duo 270c without main and PRAM battery - I started my next attempt:

I connected the PB via my NewerTech UltraDock 16sce to my Apple Studio Display 15" (M4551 rev. B ), to see if the screen of the PowerBook still wants to go to sleep without pressing the brightness control button all the time.

And it works: the PB screen never wanted to sleep again without permission. A power management "one weeks reset feature"? :beige:

But there were still some irregularities: disappearing parts of the desktop menu for some minutes, sudden hangings or shut-downs and sometimes RAM error sounds at startup, which always disappeared after a new startup.

May the power supply with the burning capacitor delivered wrong voltage to the PowerBook and damaged the RAM module?

After I installed a SCSI2SD adapter before, I installed another memory module - 20MB and booted the PB again.

Bingo! After several days of usage with and without the Apple Studio Display, this rare Duo works like a charm!

I'm really happy now! :)

PB Duo 270c Studio Display small.jpg

PB Duo 270c SCSI2SD small.jpg

PB Duo 270c - Sys 711.jpg

PB Duo 270c - Sys 755.jpg



Well-known member
I opened the Duo power supply by force because the capacitor burned a hole in the case. PowerBook 1xx power supplies have already been (carefully) squeezed with a vice and successfully opened.