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Powerbook 100 Schematic or Test Point Chart? tldr ;-)


Trying to repair a PB100 that sat stored away in a box and un-used for the last 15 years. Both the main battery and the storage internal cells had been removed before storage, so no battery leakage issues anywhere. When I first started the project, the minute you plugged it in without touching a key or anything, the screen backlight lit but nothing else happened - no sounds, no noises. So I took it apart and recapped the entire motherboard, CPU daughterboard, and even the back of the display itself and the inverter board - every electrolytic cap both the radials and SMDs were replaced in the entire machine. The smds were definitely crusty and leaky underneath - every single one, however the traces and pads were all fine and there is no evidence it spread anywhere else - the board looks pristine, but I went ahead and scrubbed top and bottom with 99% alcohol and rinsed it again with alcohol just in case. The radials looked fine but since I had it apart I replaced all of those as well. I also opened and recapped the two different power bricks it came with which were full of goo inside, but they cleaned up and now recapped both show a solid 7.8 volts and the PB responds exactly the same with either brick.

The symptoms now are when first plugged in it is dark and off as expected, and when you touch a key to power it on, the backlight lights, the screen is a solid blackish blue with identifiable square pixels, you can hear the HD spin up, engage and make a few normal sounding chirps then hear it steadily spinning, however there is no chime and nothing ever appears on the screen. I connected an ADB keyboard to the port and it also works to power on the computer too, so I think at least the PMU section must be working to operate the power-up sensing as well as sending voltage to power the drive. If I press and hold both programmer buttons it powers off and then does the same thing again. I tried removing the HD connector and modem, and even the extra RAM card and still get the same symptoms. I also have the external floppy but when it is connected it doesn't do anything at all, not even a sound. It's like the CPU is never actually booting. Without a schematic of any kind I'm not even sure what some of the chips or FETs do so I'm kind of lost on where to begin. I do measure 5.1 volts on many of the Vcc's of logic chips that I can find diagrams for and on a couple places on the CPU daughter card. I get -18.9 volts on C22, but am not sure what that goes to - I found some threads on here that suggested that was part of the display power? I get no audio chirps, beeps or even static, but the speaker is good (even tried headphones too) and one time after leaving it on for over an hour the speaker did make a couple squeeks and static-y chirps out of the blue, but after powering off and back on that hasn't repeated itself. On +C24 which appears to go to IC LT1072CN8 pin 7 (Vsw) I get zero volts. That IC seems to be a switching voltage regulator and I get nothing on the Vin or Vsw pins which I think might be indicating something somewhere is dead...just not sure what it really does or where it's source is from without trying to manually flip the board numerous times and try to draw it out by hand...which I was hoping I wouldn't have to do :) The Apple Service guide is way too generic and mostly just says replace motherboard or replace daughter card and gives no real technical repair data, and I really cannot locate anything else that has more information. So if you've made it this far...would anyone have any kinds of PDFs or documents to share - even test point values would be helpful since without a schematic it's like a guessing game. I'm fluent in electronics and reading schematics, and also rebuild and work on a lot of computers, especially old Macs, but this is my first PB100. Thanks for any pointers in advance!!


Well-known member
Not sure I can help with the non-booting issue, but one thing to check is the inductors near the C20 and C25 capacitors (desolder them). They're susceptible to corrosion from the caps and can cause the blue screen you're describing. I'm not sure if it's possible for the inductors being bad to cause the computer to not chime, but it's a good thing to check. Doubtful in this case, but at this point why not.

Also gonna @techknight here, he knows a ton about this stuff.


Well-known member
How long did you hold down both reset+interrupt buttons for? - 15 seconds with power connected? (instructions say to have all power removed, I discovered it worked only when plugged in).

I found these buttons difficult to push reliably with my fingers… The screen went from blue/black to ‘off’, I pressed the space bar, it chimed and booted up normally.

This was a Powerbook 100 that was new to me. Before this successful reset, I had replaced all the caps, but was still left with a blue/black screen and a non-booting machine. My other PB100 had the blue/black screen AND booted normally; that was the small 10uF caps near the trackball at fault
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PowerBook 100 is based on the (backlit?) Portable and there are schematics available for the Portable. I've often wondered how much might translate to the 100 as the basis for building its schematic? Might be worth a look to see if it might answer a few of your questions or provide a jump off point?

@techknight how much crossover do you think there might be? WAG here would that ASICs replaced some of the discrete components, but such should be connected to all the right stuff for condensing the block diagram/schematic?

Brings up another thing I've been wondering about: is is safe to run the 100 sans main battery? Are we chancing it? Would wiring up the likes of the readily available battery used in the portable.
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Well-known member
The Power Manager (PGMR) chip between the Portable and PowerBook 100 is the same (same Apple part number, same number of pins, same package).