Macintosh Portable, worked, now doesn't

[flecom]

So I recently refurbished my backlit portable, cleaned up and recapped the logic board, and replaced the original battery with a 6v 4.5ah lead acid battery... was working great no issues... shut it down, plugged it in to charge overnight and now it won't turn on... checked battery voltage is ok (floating around 7v) and AC adapter is putting out 7.53v and sinks 1530ma so it seems right on...

Tried removing all power for a while by removing the ac adapter, backup battery and main battery... then reconnecting main battery but still nothing, anyone have any suggestions?

 

[BadGoldEagle]

Try holding down both reset and interrupt for 10 seconds, sometimes it helps.

 

[techknight]

you could have a broken trace near the bottom corner of the LB where the 2 buttons are, and the 3 caps. one of the traces will open, its hard to spot and will cause this very same symptom. 

 

[flecom]

you could have a broken trace near the bottom corner of the LB where the 2 buttons are, and the 3 caps. one of the traces will open, its hard to spot and will cause this very same symptom. 

I'm going to open it up and check those out, I left the batteries out for ~24 hours, reconnected the main battery and it came right up... so not sure if that changes the diagnosis

 

[techknight]

nope, not really. There is a lockout latch for the 5.2V regulator, its designed to lockout the system at 5.8V and under, and its guided by the 10uf cap next to the 2 1uf caps. if any of that gets screwed the system will get stuck either in a latch-on, or latch-off state. The state is really indeterminate. 

 

[flecom]

I will check the traces on that cap, thanks for the info!

 

[flecom]

so the cap you are referring to is C26? the negative leg has continuity to U2L but I can't quite figure out where the positive leg of C26 is supposed to go, it's kind of covered by the keyboard ribbon connector

 

[flecom]

also there isn't a 10uF cap near the buttons, just 2 1uF and 1 47uF cap... I found it goes to a via and I seem to have continuity

 

[techknight]

it connects between the top left corner two pins on the OP-AMP if I remember correctly. I am going by memory here. 

 

[flecom]

there was a test pad right near it after a couple more vias I verified continuity is just fine so I don't think a bad trace is the issue at least not coming off that cap...

I did notice however I replaced the 4.7uF cap by one of the voltage regulators with a 47uF cap (doh!) so I replaced it with a 4.7uF to see if that makes any difference

 

[techknight]

did you test it at the 2 pins of the op-amp? as I mentioned? there is a very specific reason why I asked about that. 

 

[flecom]

ok, the "top left" pins of the LT1179 would be 16 and 15 which is D out and D inverting input

the negative side of the cap has continuity to D inverting input (pin 15)

positive side of the cap seems to have continuity to D non-inverting input (pin 14), at least the test pad that had continuity to the + side of the cap did for sure but the continuity from the positive side to pin 14 seemed intermittent, like if I was measuring across another cap or something when I realized it seem to change depending on how much pressure I put on the probe... I examined the trace and it looked pretty toasted going to the via, so I ran a lead from the positive side of the cap to the test point and have reliable (0 ohm) continuity now, so lets see if it holds up

 

[flecom]

ok well now it boots fine when it's plugged in, unplug it and it continues to run on battery... but if I try to start it on battery I can hear the drive trying to spin up over and over but won't start (battery is sitting ~6.4VDC and dips to ~6.2VDC when the drive tries to spin up)

 

[techknight]

the boost converter circuit may not have enough current at a lower voltage to fire up the HDD. That would be in the boost circuit. Maybe one of the caps didnt quite grab the connection there? Hard to diagnose that.