Mac Portable Power Woes (what else is new?)

[NJRoadfan]

Got my battery today. It appears to be charged. The charging circuit appears to be working without a problem with the stock AC adapter. Battery tests good with about 6.4v at the terminals. Strictly powered by said battery it appears I'm not getting enough voltage on the 12v line. The floppy drive makes a groaning noise (trying to seek) and the hard drive just clicks with no attempt to spin up. When I plug in the A/C adapter, the floppy drive quiets down and the hard drive attempts to spin up and then fails.

All caps on the logic board have been replaced except for the one at C3 (220uF/25V) since I didn't have one on hand. Would this cause power problems like this? Is there an area on the logic board that I can test the 12v and 5v lines to see if they are working correctly?

Hmm, looks like I may have the same problem as this guy: viewtopic.php?f=10&t=20839

 

[NJRoadfan]

I don't know what the heck I did, but it works now!

When I tested for 12v at the HD and floppy connectors, I was only getting battery voltage. I took the machine apart to do some more probing and I guess something popped to life because from that point on, I started seeing 12v on the motherboard again. Reassembled the machine and now I have a working and booting portable!

 

[NJRoadfan]

Its ALIVE!

 

[uniserver]

the 4 100uf caps, they always corrode up the holes they go through.

Sometime if you wiggle or touch them they will make a connection.

The best thing to do is pull those for 100uf radial caps back out, and flood the areas with flux and scrub those areas with the soldering iron and solder wick, should make those through hole pads shine again.

 

[NJRoadfan]

I lost 12v again shortly after taking the video. I think the problem was a short between the motherboard and bottom of the case (the RF shielding appears to be conductive). Some of the legs on the axial capacitors were still a little long after cutting so I insulated them. I also have to replace C3 now that I read that its part of the booster circuit. Occasionally I get a crackling sound from the speaker (you can hear it happen in the video), which I suspect is that cap acting up. When I replaced the other radials, I did a pretty through cleaning of the area as they had leaked pretty bad. If I have any further problems, I'll rip them out and clean it all again.

 

[techknight]

ALL SMD and Through hole capacitors REQUIRE replacement in this situation. all portable machines that use a single voltage, use multiple DC-DC converters to generate the other voltages required to make the system function, and these are critical to have good caps for proper operation.

And not to completely rule out some out-of-tolerance resistors in the regulator circuits as well. Rare, but can happen.

 

[NJRoadfan]

ALL SMD and Through hole capacitors REQUIRE replacement in this situation. all portable machines that use a single voltage, use multiple DC-DC converters to generate the other voltages required to make the system function, and these are critical to have good caps for proper operation.
And not to completely rule out some out-of-tolerance resistors in the regulator circuits as well. Rare, but can happen.

They were replaced except for C3, somehow I forgot to order that one. I'll add it to the list when I do another capacitor order. So far I haven't had any problems with the 12v line once I insulated those long leads.