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Macintosh Portable Restoration Help

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raoulduke

Experienced Member
Joined
Jan 14, 2015
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This is preemptive. I'm almost done recapping and I'm convinced it's not going to come out of that working properly. If it does this thread will result in a pretty picture.
 
When I first powered it up I got random line patterns on the screen. After recapping it I get slightly different line patterns. One of the solder pads lifted off but I'm fairly sure I repaired that. And my initial repair (basically attaching one side of the cap to a hanging-on solder pad) didn't yield any different screen results than my eventual repair when the pad fell off and i soldered it to the trace.

I can tell it's not getting to or past ROM because it doesn't really check for a disk. I also tried it on an external monitor before I recapped also with no result.

I don't think this is an issue with the temperamental power up. I was going to post a video but I don't think that's going to help at this degree of generality. I'm curious what people would start doing next. I've also washed the board.

You know I thought this at first but then lost the thought: could it be the RAM? Wouldn't the RAM test precede checking disk? There's no startup chime, though I do hear brief speaker fuzz when it turns on, so that suggests it could be RAM or processor. I see several candidates for dead traces on the underside of the board.
 
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I know very little about the Mac portable. I have used one many years though. Some general thoughts: Do you have a scope around (or better yet logic analyzer)? I would trigger on processor out of reset and then the CHip Select for the ROMs.. Does it actually get out of reset condition? Does it try to fetch the reset vector from ROM? I.e. Is the address decoding working? Is the CPU clock running properly? Broken crystal oscillators do happen.

Is there a schematics available for the Mac Portable somewhere?

Good Luck!
 
Thanks.

Yikes. No I don't have a logic analyzer but I should eventually get one. And I lack expertise (now) to do the other stuff anyway. I'm going to - or my thought is - to basically repair all the traces that have dead spots. I don't know how realistic it is to repair the traces themselves because they are so close together and the faults tend to be across a series of them, so I think it'd be too close together. So I'm hoping I can just bridge various pins. At that point; I don't know how long that will take me; then we'll see what we have.

I can get it to power on and I can get it to shut off. I can't get it to reset by itself. I'm not sure if any of that indicates the CPU is actually functioning. However the fact that stuff shows up on the screen may suggest that the video chip initializes and it fails on RAM or something; I don't know if those indicate CPU activity. But with those traces dead I think this is basically all moot. I'm just concerned this is going to test my abilities and I'll screw it up.

I have a Powerbook 100 I have to recap that... I truly hope lol... doesn't have similar issues. I recapped it once to no effect so I think I either have a dud cap or screwed one up. I have another set; I might redo it all in stages.
 
So to do some of these repairs I'm going to need to bridge vias. Should I just basically solder a wire from one via to another? [Like... it's a little hard to impress how much finer this work is than what I'm used to. My first concern is actually being able to trace the traces themselves. But there's no way I'll be able to actually repair most of the traces.]
 
If you're going to be doing VIA/trace repair, you'll want to test those connections and make sure that they don't have a short to ground anywhere. If there's a short to ground inside the PCB then you'll have to lift component legs and make jumper wires external to the PCB.
 
If there's a short in the component legs (by which I am inferring you mean of like the RAM chips on the upperside of the board (which is where this is probably a problem)) then I'm screwed. What a shame.
 
Finding a short on surface traces would be a good thing because you can just start pulling chips until the short clears. What I was referring to is if there's a short to ground in one of the inner layers of the PCB, you'll have to do more intricate surgery to remove any IC legs using the offending trace(s) and route the lines externally on the board, which can be a nightmare.

But to do this sort of stuff, you'd really need a logic analyzer and a bench power supply so you could inject power to specific parts of the board. If you find a part with excessive current draw or that gets really hot then you've found a problem.
 
There's a fellow who goes by the handle TechKnight over on the Mac 68K Liberation Army site ( https://68kmla.org/forums/ ), and he knows everything there is to know about the Mac Portable. He can advise on repair, or he can do the repair. Perhaps you should ask some questions over there before you depart into unknown territory?

Just a suggestion.

smp
 
Gigabyte. Yeah those types of board-level repairs... if that's the case then I'm screwed. I agree with you; I'm just explaining there's no way I can do those types of repairs. I'm accepting my limitations... I will get a logic analyzer (over time) but I'm not optimistic that my skills will change there. (Any suggestions on which (cheap) one to get?)

Thanks smp; I know TechKnight. I have beef with 68kmla; I've considered posting this there though. But maybe I'll just reach out to techknight and uniserver. I think I need to try to wire up some of the traces first just because I'm pretty sure they'll both tell me two things: 1) try fixing the traces; 2) send it to us. It's a good suggestion smp. Thank you both.
 
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