Macintosh Portable issues

[bd1308]

I'm working on a fix for this, but how many users do we have here that have a Macintosh Portable with a drive that does not successfully startup? Typical symptoms include a spinup and spindown, followed by another spinup/spindown until either the battery dies or the system errors out.

I have a backlit portable and a non-backlit portable, and Ive found that the power management 'section' of the board is....not great. Fairly newly developed ICs are far better and more efficient when dealing with power management and supply of clean power, so i'm testing a design which allows the supply of clean 12VDC to the drive to allow proper startup of the drive itself.

I'm also experimenting with an implementation of a SCSI->IDE converter and using a CF card instead of the hard drive, which should lower power requirements significantly as well.

 

[shred]

What sort of state is the Mac Portable battery in?

The Mac Portable absolutely needs a good battery installed before the hard drive will spin up. This is because the AC Adaptor alone cannot produce enough power to reliably start the hard drive spinning. If the battery is not present, or has an unacceptably high internal resistance, you'll see the backlight (in that particular Mac) dim as the computer attempts to crank the hard drive up and fails.

It used to be possible to buy the Gates (now Cyclon) lead acid cells used in the Portable battery and re-pack the battery. I converted my Portable to using a 2.5" PowerBook SCSI drive many years ago and this fixed the "needs good battery" problem for me. My Portable now has a Compact Flash card as its "hard drive" and this is a very satisfactory solution (so far), since it's now a very quiet computer. I put up a post on this about 18 months ago.

 

[bd1308]

Ive been on close contact with Houlton, who rebuilds and sells Portables on ebay. I have purchased a brand-new rebuilt battery last year, and the portable remains plugged in 24/7 at work.

 

[bd1308]

I've also acquired a bunch of motherboards with various problems. One a random note, washing the motherboards in the dishwasher seems to help clear up the leaked electrolyte from the caps, and seems to restore (temporarily) partial/full functionality.

Anybody have a link to the ol' Mac Classic tips for replacing caps?

 

[H3NRY]

I looked at a bunch of bad backlit portable mobos for Houlton, and all of them had problems with the 5V power regulator, as does my own 5126. Apparently the integrated voltage reference gets flaky with age. Capacitors don't seem to be as much of an issue with backlits as with the original 5120s, nearly all of which have leaky / dried out electrolytics.

I never managed to trace out the circuit or work out a fix for the 5V regulator in backlits, and I think the best approach is to simply replace that section with modern parts. One of these days when enough other projects get cleared off the decks, I'll have at mine. This often produces the spin-up, shut down, spin-up, shut down behavior.

Bad caps in the non-backlits do the same. The problem there is noise on the power supply outputs, which can show up as flickering or strobing of the screen, failure of the floppy to read disks, no sound one or both channels, etc. Replacing a bunch of caps is the answer. There are meters which can measure capacitors and inductors, called LCR meters. They can measure a cap in circuit to tell you whether it needs replacing or not. At this date, the majority of caps are either completely dead, or less than half their rated capacity in the portables I've looked at, so I'd just plan on replacing them all.

Last I checked, my local Batteries Plus store had the cells for Portable batteries for about $35 for three.