Symptoms of Mac Portable not getting enough juice?

[Byrd]

Hi,

My current project is resurrecting a (non-backlit 2MB RAM/40MB HD) Mac Portable, which I've had sitting around for years - I recall it used to chime but never got much further than that. Thought it was flaky due to leaking caps; took it apart (what a breeze!), and discovered the brown ooze on the corners of the case was probably spilt coffee I cleaned it all up, and decided to replace all the caps whilst there - they didn't look bad, but after removing them I noticed some of the small can electrolytic caps had a clear slimy residue underneath each one when removed. So either way, it probably wasn't a bad thing to do. The whole recapping job took a lot longer than thought, however

Put it back together, and mistakenly plugged a square 9V battery into the holder - it let out a "fzzt!" sound and I couldn't get it to power on, pressing all the interrupt/reset buttons - and using a Powerbook 7.5V 3.0A power brick to turn it on. Double checked the motherboard: all seemed OK.

Left it for a day, and plugged it into the 3.0A power brick again: chimed, hard disk span up and was presented with a DiskLock password screen to get in. Success! Had to get to work so quickly switched it off.

Got back home, and these problems occur ...

- With just the power brick + 9V battery, it chimes every time but resets whenever it tries to probe the SCSI bus or floppy disk. With the hard disk unplugged and floppy removed, I can get to the flashing disk icon. Put in a floppy, reset. Does this continuously until perhaps coming up with a Sad Mac after ~ 10 continuous resets.

- It won't power up at all unless the square 9V battery is installed. Actually, even if the power brick isn't plugged in the Portable will chime and try to turn on with this battery plugged in - quite a feat!

- Does nothing with the (dead) 6V battery plugged in

I've read around Mac Portables not starting up because the large lead-acid 6V battery was dead, and the Portable essentially runs off this. I've noted people hooking up a +6V DC power brick to the battery terminals and it's OK. I've also read about people using the Powerbook 3.0A power brick, and getting around these issues - it starts without a problem.

Am I getting symptoms of a Portable that's not getting enough power, based on the dead 6V lead acid battery?

Thank you

JB

 

[shred]

It does sound like the usual Mac Portable with no main battery problem.

Don't forget that the 9v backup battery is only in circuit when the lid is off the battery compartment. The reverse is also true: if the main battery is installed, it's only in circuit when the lid is on the battery compartment.

 

[ClassicHasClass]

For my Portable (WITHOUT the battery or 9V cell), the magic numbers to the power supply were 9V and 3A. This powers up the original Conner drive and the FD reliably.

 

[Byrd]

Ah - so you ran that through the standard power socket? That sounds a lot easier than having to re-wire the 6V lead-acid battery housing.

 

[geeko]

Can a 12V, 2.5A power supply be used? That is the only stronger PSU I have with me, and I have 2 portables I'd like to get working. (I may have others, I'll have to look again if everyone here thinks this is a bad idea.)

 

[Byrd]

I wouldn't use that - the standard Portable power brick is 7.5V 1.5A, so pushing 9V xA through it sounds feasable - but magic smoke may be released if you try for 12V

JB

 

[Osgeld]

depends on the regulators used inside, 7.5 volts is just enough to make a standard issue 7805 work, and they handle 20+ volts (if you have jack crap load and a large heatsink)

that doesnt mean anything though, if the battery is going though the same device then its something different, like a low dropout device, which often have a MAX of 12 volts

anyone got a schematic?

 

[H3NRY]

The Portable's internal regulator is a switching supply designed by Apple. I don't know what the min & max input voltages are, but it will run on as little as 5.7 V from a discharged battery and as much as 9 V. The input capacitors are 16 V rated, I think, but I'd be nervous about applying 12 V anyway. Since the 6 / 7.5 V supply is stepped up to 12 V for the disk drive, it might not be able to cope with stepping down. I've been looking for a schematic, too. No luck so far. If one exists it's probably buried in some dusty cardboard filing box at Stanford.