Powerbook 100

[imactheknife]

Well, had a powerbook 100 that worked when I brought it home. Next power on, infamous black back lit screen. cleaned and recapped it, nothing, no change.. last one of these i buy.. two useless laptops.. anyone need a nice display or two??

 

[Cedsrepairs]

these are extremely difficult and frustrating to repair
I just finished my second one. It works - but this time I swear I am not touching a PB100 again.
The screen recap in particular is atrocious.
The mainboard uses that painful varnish that becomes sticky when cleaned with IPA
All the 1uF capacitors leak.
The harddisk has sticky heads, replacing it with an SD costs more than the price of the PB100 itself
The inverter never works "as new" even when recapped (the brightness range is wrong).

And none would buy any of those fully working units from me at any decent price. Heck - I wouldn't either.

It's a leap of faith.

 

[3lectr1cPPC]

The mainboard uses that painful varnish that becomes sticky when cleaned with IPA

So that’s why! I assumed it had just spread the flux I used all over the place instead of picking it up but I guess not. Wonder why that is. What specifically do you mean with the inverter board? Brightness or contrast?

I didn't find the actual recap that bad, maybe I'm used to difficult designs from fixing other PowerBooks though. Display recap is pretty easy if you get it down to just the LCD, removing all the frame and backlight layers from it.

 

[Cedsrepairs]

Nah there are a few vintage computers that share this awful varnish that makes a sticky goo when you try to clean it with IPA, the PB100 is one of them. You've got two solutions ; either you don't ever touch it with IPA, or you wipe it entirely by pouring a large quantity of IPA on top of the board, brush it until it's all gone and doesn't stick anymore... (but easier said than done)

The brightness : I've repaired three PB100 inverter boards and none of them seem to work properly after recap. I believe it's the potentiometer itself that's not working well, some active component, or maybe the tube itself (which by the way consumes a LOT of power, more than half the power a PB100 draws is the LCD backlight)

 

[3lectr1cPPC]

What behavior is the inverter board showing? Is the backlight too dim? My brightness dial seems to work properly but it does start a bit dim? Maybe not abnormally so but dimmer than my other PowerBooks. Not even close to unusable but dimmer. If anything, my contrast dial is the one with issues. I can get a great range of usable contrast and the screen looks really good, but at the lowest setting, I can still see the image clearly. On my other PowerBooks it will fully darken.

 

[Cedsrepairs]

Well it's like the first 1/10th of a turn is black, all off, then all of a sudden it's 90% bright, and the rest of the range (nearly all of it) is going from 90% bright to 100% bright. What's bizarre is that it's the second time I repair a screen that behaves exactly the same, so either I'm very unlucky, or I do something wrong.

 

[3lectr1cPPC]

May just be how these are. All my early PowerBooks behave like this.

 

[Cedsrepairs]

What is also possible is that they chose logarithmic potentiometers and not linear ones (for whatever reason).

 

[3lectr1cPPC]

What's the difference? Electrical component noob here.

 

[Cedsrepairs]

Well most of the potentiometers are linear nowadays

In the 80s as they were mostly used for (audio) volume, a lot of them were of the "log" type ;

Log and Lin Controls

Variable Resistors and Log and Lin Potentiometers. Linear and logarithmic or tapered types of track for different applications. How to make a linear potentiomer logarithmic.

learnabout-electronics.org

Basically the range is not linear ; if you do half a turn, you're not at 50% of the resistor value, you're at much more than that. (or much less depending which side you use)

So what could explain the weird behaviour of that brightness knob, if this is indeed stock, is that they decided to got for a "log" potentiometer... You could measure to confirm actually.

It could also be that the light tube is old, and doesn't light up like it used to... idk

 

[3lectr1cPPC]

Hmm. There’s gotta be a way to test that, would be interesting to see. The pots used on the 100 are also quite loose and easy to turn compared to the sliders on other models.

 

[CC_333]

Well most of the potentiometers are linear nowadays

In the 80s as they were mostly used for (audio) volume, a lot of them were of the "log" type

That makes some sense, and since Sony (which at the time was primarily into manufacturing A/V equipment, I think) manufactured the 100 for Apple under contact, it follows that the 100 might have some odd design decisions that are unlike virtually every other PB, such as, for example, the use of (possibly of the logarithmic, audio type*) rotary pots for brightness/contrast instead of the (presumably linear) sliders found on all other members of the 1xx family (save for the 190/5300, which used push buttons).

Until someone tests this hypothesis, it's hard to say if this is actually true or not.

c

 

[3lectr1cPPC]

Well, my PowerBook 145 and 170 also show the same behavior described.

 

[rollmastr]

Same here with a PB 160 and 165. I even recapped the inverter board of the 165 and noticed no change whatsoever.