PB 100 recap woes

[JRL]

So recently I picked up a 4th PB 100 for $25 shipped, as the screen looked nice and all of my working PB 100s have screen rot. Figured I'd give a crack at actually fixing it before parting it out.

Recapped all radial/SMT caps and LCD (also booting from a recapped PSU of the proper voltage) - chimes as normal and the repaired Conner HD spins up but I get a solid blue/black screen. Contrast controls are unresponsive. 

I tried the newly recapped LCD with my other working PB 100 and it works great, so the fault is somewhere on the board. All of the traces near the caps have tested fine. This board has the fuse fix applied from the factory.

Has anybody else dealt with a dead/flaky PB 100 after recapping everything? Of note, I didn't follow uniserver's cap reference, as the values were completely different on this board. My board's values matched the board pictured in this guide:

https://goughlui.com/2016/09/24/repair-apple-macintosh-powerbook-100-gotta-re-cap-em-all/

 

[Byrd]

Hi JRL,

Did the same thing just recently, recapped the PB100 motherboard, back of the LCD - on a pristine unit that wouldn't boot, but the LCD remained black.

Now it chimes, boots to desktop - but the LCD remains black.  If you look through the forums "PB100 black screen" is a common fault but yet to be determined and past discussions have revolved around the LCD controller and inverter at fault.  It's interesting however that the issue appears not related to the LCD, inverter - but the motherboard itself.  Where we go from here though, I couldn't say.

Like you I've some spare parts at my brother's that I'll attempt to find a good motherboard to work with the LCD, which I suspect is fine.  But I'd love to learn the main cause of the motherboard issue here.

JB

 

[JRL]

For those wondering, I found the issue - it was the adapter. The PB 100 boots great from my PB 150's "low power" adapter. Guess one of the ICs in my recapped adapter went bad - this PB has an additional fuse fix from the factory so it could be drawing more power.

 

[Byrd]

Fixed the black screen issue?  I'm at a loss with mine, need to find a donor PB100.

 

[JRL]

Hey Jordi,

Yeah, with my 150s “Low Power AC Adapter” it works great now. I would give it a try if you have one spare.

 

[Byrd]

I'm sceptical but possibly ... dodgy PSU could be the cause - there are lots of reports of "blacklit screens" on many PB100s

 

[JRL]

I'm sceptical but possibly ... dodgy PSU could be the cause - there are lots of reports of "blacklit screens" on many PB100s

Yeah, my recapped original PB 100 PSU would never work right with any of my PB 100s that had the fuse fix applied from the factory. Even on the ones I have without the fix it would work, but there would be odd issues such as the screen flickering when I pressed a keyboard key. I think it's likely a semiconductor in the psu that's the problem.

 

[Byrd]

Spent a nice Sunday afternoon with some success resurrecting three PowerBook 100s - all were recapped a couple of years ago, with the cleanest and best looking board booting but causing a "blacklit screen" as noted above.  I went back to these as the tantalum caps and electrolytic caps I had used were of dubious quality and felt I hadn't cleaned the cap goo off well enough previously.  And also, I just really wanted to see a working PB100 after three duds lying around

- Powerbook 100 # 1 - the best board - checked all caps (good), found I didn't replace the 100uF/10V capacitors - did so - same as before chime, boot and "blacklit screen"; tested the other to LCDs with same effect.  I suspect the issue lies in one of the three transistors in the middle of the board (one had a clip on it that extends to touch the keyboard when down as a basic heatsink).  But that's where my electronics experience stops.

- PowerBook 100 # 2 - cleaned all cap regions with IPA and cotton bud, replaced and tested some dubious tantalum caps (yep, three were the wrong way around), fixed a broken pad - success, booting well to desktop

- PowerBook 100 # 3 - cleaned all cap regions with IPA and cotton bud, replaced and tested some dubious tantalum caps - success, booting well to desktop

So it was the best pristine unit I couldn't resurrect but two others came up well which was pleasing!  

Now to the LCDs - all three have an small odd pink patch on each, looking a bit like a fungal growth/moisture ingress or LCD is damaged.   One recapped has good contrast and brightness, the other two LCDs untouched have poor contrast and brightness.  I'll donate one LCD to experimentation and strip down the LCD layers - it might be the top polarising film that's damaged.

JB