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Powerbook 100

cleaned and recapped it, nothing, no change
I’ve recapped a whole bunch of PB100 recently and they all had the backlit blank screen issue. The first one which I recapped with tantalum caps still had the same symptom when I retested but weirdly worked perfectly the next day. But a few days later it started randomly doing it again. It is still unreliable.
I read online that tantalum caps are not functionally identical to the original aluminium electrolytic caps as things like frequency response vary so in some circuits they are not suitable replacements. I don’t know enough to know if that’s the case here but I thought it worth a shot so recapped one with direct replacement aluminium electrolytics and this works perfectly and reliably. I have now recapped another 4 logics the same way and all have worked so maybe they something to consider. I know they may not have the same longevity as tantalum but on the plus side, they seem to be a lot cheaper.
 

Cedsrepairs

Well-known member
Always used electrolytics ; never had this problem
Also tantalums are way more difficult to stuff in the screen
 

alexGS

Well-known member
I don’t know enough to know if that’s the case here but I thought it worth a shot so recapped one with direct replacement aluminium electrolytics and this works perfectly and reliably. I have now recapped another 4 logics the same way and all have worked so maybe they something to consider. I know they may not have the same longevity as tantalum but on the plus side, they seem to be a lot cheaper.
I second this; I use electrolytics on the logic board (the Wurth Electronik ones from Mouser) and haven’t had any problems. I’ve done six now. Actually I love the PowerBook 100; I’m so much more successful with those than I am with other failed PowerBooks. Especially the 20MB hard drives - a drop of UV-cured Bondic resin stops the head arm getting stuck on the magnet, and away they go.

Meanwhile I don’t know which is best to use on the back of the Powerbook 100’s LCD; I’ve used ceramics, I’ve now obtained tantalums for the next one, after someone said the contrast can never be stable with the ceramics. It is true that I usually have to adjust the contrast as the display warms up.

Does anyone have a suggested source for replacement polariser film? I have two PowerBook LCDs that are working but exhibiting ‘vinegar syndrome’ (bright yellow glow in the centre, OK around the edges). The film I’ve found so far gives a sepia-tinted ‘white’ and purple ’black’.
 
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3lectr1cPPC

Well-known member
Interesting notes on the caps. I used tantalums on mine and it’s doing ok. External SCSI and the reset button are the only things that have been wonky. The reset button just doesn't work, probably a broken trace somewhere. The SCSI though is stranger, it does work, but if I plug in my PiSCSI and then try to boot, it goes to blank screen no POST as soon as I plug power in.

I forget if it was that it would work if I started with the the PiSCSI connected but with no drives mounted to it, or if it was if I hot plugged it after the PowerBook was started and then rebooted, but it does work after that.

I'd avoid ceramics on the LCD. They do seem to work ok on the early STN/passive monochrome LCDs for the most part at least, but yeah my 145 that I did with ceramics can have some driftyness at times. Plus I have no idea if this is related, but my PB 100's LCD looks incredible for a passive STN screen. I get practically zero artifacting. Could be that the tantalums really work well on it compared to ceramics, but my 145's LCD is worse in the artifacting/lines regard, although it's still good. Maybe I should go and re-recap my 145's LCD with all tants as an experiment. Also could just be though that the 100's LCD is better quality. After all I recapped my PowerBook 150's LCD with tantalums and it still doesn't look very good artifacting wise.

@imactheknife - are you gonna try electrolytics on your boards now? would be good to know if this is actually an issue or not.
 

aplmak

Well-known member
The PB100 is exactly the same as the Macintosh Portable.. 68000 just condensed into a mini form factor. I wouldn't doubt the programs crashing.. I experience the same thing..

I've recapped many, many, many of them and almost started a production line to doing them getting into a groove. Besides the logic board which I don't have too much trouble with, I always do the caps on the display inverter board and the leaky caps on the LCD display.. I think they are 3.3uf and I have managed to find some nice A case SMD's that work great. Before that I had some tantalum dipped that were very small but I had to angle them a bit awkwardly. And yes the damage to the screen with the purple patch is annoying.. The most important thing is when storing them you remove the trackball. Even the keyboard can effect the screen. I try to throw some rubber bumpers between the screen bezel and the palm rests when storing. I also store them vertically instead of flat to alleviate less pressure. But the key is to remove the trackball.. just an FYI.. Mostly the reason why is the gooey top bumpers of the screen have collapsed and squished down allowing the screen to come in contact with the trackball and keyboard. The worst thing you could do is stack them ontop of each other.
 

3lectr1cPPC

Well-known member
yeah my 100 is stored vertically (all mine are to save space) and the trackball is removed 100% of the time when I'm not using it, not chancing it on my screen.
 

alexGS

Well-known member
Well, what a job :D The frustration of stripping tiny bits of wire did not get the better of me… and I was rewarded with nice stable contrast compared to the MLCCs. No need to adjust the contrast as it ‘warms up’ now.

Would have been so much easier if I could have ordered shorter tantalums from Mouser, but they all seemed expensive or not in stock… next time, hopefully.

Also, I agree with everything aplmak said :)

IMG_4852.jpeg
 

alexGS

Well-known member
With some honourable exceptions, MLCCs have poor temperature stability, so it's not surprising you'd have to twiddle constrast as it warmed up,
Cheers, yes, I’d read that and can now confirm that’s my experience :)

Sorry about what looks like a horrible mess how I’ve fitted the tantalums, but there are no shorts and the hot glue will prevent any movement.

Meanwhile, here’s the next PB100 display I have to fix. I mentioned this above, I’m not so excited about ordering new polariser film now that I realise it has dead lines as well…IMG_4849.jpeg
 

alexGS

Well-known member
Now that is creative bodge work, bravo!
Haha, thanks :)

Speaking of bodge (wires) - Possibly this is a good place to ask - some 100 logic boards (about half the boards I see) have various resistors added in pairs onto the VLSI chips and strung across other places as pull-downs to ground, but always the same places. Looks like it was a technician mod ‘in period’ but I haven’t found info about it anywhere. Do we know what it actually achieved?

Every time my own PB100 unexpectedly quits with error 3, I wonder if it’s caused by not having the resistor bodges installed that I’ve seen on other boards. It’s basically the same mod that was shown in https://68kmla.org/bb/index.php?threads/identify-a-mod-on-my-powerbook-100.43181/ except without the PCB and just with resistors/white paint/glue/tape instead.
 

imactheknife

Well-known member
I’ve recapped a whole bunch of PB100 recently and they all had the backlit blank screen issue. The first one which I recapped with tantalum caps still had the same symptom when I retested but weirdly worked perfectly the next day. But a few days later it started randomly doing it again. It is still unreliable.
I read online that tantalum caps are not functionally identical to the original aluminium electrolytic caps as things like frequency response vary so in some circuits they are not suitable replacements. I don’t know enough to know if that’s the case here but I thought it worth a shot so recapped one with direct replacement aluminium electrolytics and this works perfectly and reliably. I have now recapped another 4 logics the same way and all have worked so maybe they something to consider. I know they may not have the same longevity as tantalum but on the plus side, they seem to be a lot cheaper.
do you have the list at all? I have 2 pb100 would love to try. I used tantalums but no go. Thanks for any info!
 
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