Portable Stuck In Reboot Loop

[CC_333]

Hi,

I got a Mac Portable from Haplain, and apparently it's a bit of a fixer-upper (which I knew going in, because of my tight budget).

It will come on, but it just sits there chiming about once every second. The display is good, because I can produce a Sad Mac and it'll show up just fine.

Anyway, I was wondering if anybody had any advice. I would like to also see if maybe I could buy/trade for a working board, if possible, in the event that it's unfeasible to repair the one I have.

This board has been recapped with axial caps (the ones with both terminals coming out one end), so that should not be a problem (although perhaps there's a damaged trace from before?)

c

 

[techknight]

Your going to need to check various voltages around the board. Especially your 5v. If its low this will happen. Just like a compact.

 

[Byrd]

Also check all the batteries, etc. Mine does the same, never had the time to really nut it out.

 

[CC_333]

The battery *appears* to be okay, but I'll check it with the volt meter nonetheless.

As for the voltages on the board, is it possible a regulator IC has gone bad somewhere?

I'd really like for this to be simple...

But alas, it probably won't be (one can still hope, though).

c

 

[techknight]

thats precisely what your checking for. bad voltage regulators, or a capacitor in the regulator circuit.

 

[CC_333]

Ahh, OK!

A visual examination suggests that there's nothing visibly damaged or burnt, but I did notice that three sets of two capacitors each are of the old style. They look new, and the solder fresh, but who knows?

I'll keep looking into it...

c

 

[mcdermd]

You can try disconnecting the hard drive to see if it's too much of a power draw on a weak system. I've seen that before.

 

[CC_333]

It doesn't have a hard drive, so unfortunately that isn't the problem.

I have removed the logic board if anybody wants to take a look.

I'll check out the voltages at some point today and see what's up. Can I use the external floppy port the same way as with the Plus?

c

 

[uniserver]

Can I use the external floppy port the same way as with the Plus?

yeah man

 

[CC_333]

Great!

I'll get on it shortly (I've dismantled my Mac Pro for it's bi-annual cleaning, so I'll have to finish that up first).

c

 

[CC_333]

OK, got the Mac Pro set back up, and got a chance to check the voltages.

The 5V rail is kind of high at 5.22, and the 12V is 11.92.

The battery, fortunately, is a healthy 6.49 volts.

So something else must be wrong here. All the voltages seem okay (though the 5V seems a bit high).

c

 

[techknight]

If you have a scope or a really fast multimeter the probe the reset line for noise. Also you need to monitor the 5v line continuously. This way when it reboots you can check the voltage state.

 

[CC_333]

I did watch the 5V line through several loops, and the voltage is constant.

I don't think my meter is fast enough to do logic stuff, but I suppose I could try. What is there to lose?

I'll post back shortly.

c

EDIT: Well, I couldn't figure it out, but I did discover that my multimeter has a logic mode, though it seems to only measure single digit megahertz. Anyway, I also discovered that it behaves the same way as if I was trying to boot from AC with no battery installed (something which isn't supposed to be possible with a stock charger, which I have), so something seems to be somehow wrong with the battery circuit.

By the way, do I need to install a 9 volt battery for it to boot? Does anybody have an "Owner's Guide" of sorts?

EDIT 2: I found this site. I'll look through that for any clues.

 

[CC_333]

Well, it went from bad to worse. It won't make so much as a peep now xx(

I was checking over some of the capacitors and re-soldering them, thinking maybe there was a cold joint somewhere that wasn't making good contact.

I hope I didn't fry anything

c

 

[techknight]

Did you check the fuse on the mainboard to make sure it wasnt blown? also make sure your getting your 6V to the mainboard, there is a reed switch in the battery compartment. If the cover is removed, the battery is disconnected from the mainboard and the 9V is switched in.

 

[CC_333]

I didn't think to check any fuses.

The reed switch is working, as immediately before, when I'd remove the battery cover (and thus disengage the switch), it would shut off.

I'll check the fuse next...

c

 

[techknight]

K well then the fuse is irrelevant in this case, the portable is seeing the battery.

I still strongly think you have a regulation problem, or your RESET line is going bonkers.

 

[CC_333]

Yeah, I suspect some sort of regulation problem as well (the 12v seems within tolerance, but that 5v line seems kinda high). Also it doesn't seem to be getting the proper amount of current somehow (it behaved exactly the same way when I removed the main battery, running straight off of AC).

Did you want me to send you the board so you can check it out? I'm running out of ideas...

c

 

[techknight]

Post a pic of the board. If its a backlit board i could probably work with it. non-backlit I cant because I dont have a non-backlit portable.