Monday, July 27, 2020

Refurb weekend: Mac mini G4

A year ago, I set up a Mac mini G4 as a network bridge running NetBSD (the "secret last generation" with a 1.5GHz G4 CPU), and it rapidly became one of the hardest working machines in my machine room. Last week, it abruptly ceased responding.

I went and looked at the console, and found it had thrown a couple ATA controller timeouts and then seized up completely. I restarted it and fsck started timing out on sectors all over the place. Hah! said I. The hard disk must have crapped out. It was still running an original hard disk, and those certainly fail with time, so that didn't seem at all strange to me. That means we're gonna have ... a Refurb Weekend!

Since I was expecting to replace the drive anyway, I figured I might as well make it an SSD and bought an inexpensive Kingston mSATA. The drive I was replacing was 80GB, and I could get 120GB nearly for the same price, so we'll call it an upgrade.

The G4 Mac mini only takes 2.5" PATA drives, thus requiring a laptop mSATA-PATA enclosure as well.

Let's get out the putty knife. Yes, that's really how you crack these older minis open ("crack" being, sometimes, the operative word). We jam the blade into the space between the base and the metal top case and work around the outside, freeing up the clips, until we can pull out the base.

The G4 mini comes apart basically in two halves, the motherboard sitting on the base (usually with the Bluetooth-WiFi module mounted on it, and/or the modem on older models) and then this drive cage/fan assembly that contains the optical drive, hard disk and main cooling fan. This unit has the infamous original Apple-rebadged Panasonic UJ-845-C slimline drive. These fail if you look at them crossways, and this one was already refusing to read burned CDs from certain manufacturers, but we're not here to replace that currently. The antennas on top are for the Bluetooth and WiFi, and sit under holes cut out for them in the metal of the top case. We unscrew and pull the drive cage from its logic board connector, making sure to unmount and thread through the antennae. There's a bit of Kapton tape securing these and the wires for the power button to the drive cage; make sure you peel those back too.

The drive cage is now separated from the logic board. Ugh, dusty. Blowers employed at this point on the fan blades, fan race, air intake, processor heatsink and logic board.

There are four screws holding the hard disk in the cage. The two on the exposed side are easy enough to see, but one is under the fan (the fan screws are rather tightly threaded, so they need a little bit of cranking to get out without stripping them), and the last one is only easily accessible with a shafted driver through an access hole provided for that purpose (covered, obnoxiously, also with Kapton tape).

With the screws out, a little prying (not too much, or you'll bend the card and/or the pins) with a nylon spudger will push the drive off the socket on the interposer board connecting both the optical drive and hard disk. I intended to do a little post-mortem on it, so I put it aside and picked up the new drive in its enclosure.

The main drive is actually suspended with a slight air gap between it and the optical drive; they are not flush. Wedging the spudger in between will make it easier to line up the screw holes.

With that done, I screwed back in the fan, threaded the antennae back through the drive cage on top, carefully made sure the interposer board was plugged back into the logic board, screwed down the drive cage, remounted the antennae on their mount points and replaced the top case. I got out my trusty iBook G4 to format and partition the drive, hooked the mini up to the iBook via FireWire and held down T as the mini started up ("bonnng!") to enter FireWire Target Disk Mode.

... nothing happened. The monitor stayed dark. Huh.

Well, sometimes the Mac's parameter RAM gets scrambled after a hardware change, so I reset PRAM with Command-Option-P-R. (Probably should have replaced the PRAM battery — a 3V 2032 or equivalent — while I was in there.) I held the keys down, made sure it bonged a few times, and let it try to boot whereupon it (expectedly) displayed the "No system folder" icon. The drive is of course blank so that seemed okay, so I popped in a CD I knew it would boot from, restarted the mini and tried to boot from it with the C key. Still nothing. Time to get to the Open Firmware prompt (Command-Option-O-F while starting it again) and figure out what was wrong.

A little known trick is that you can start FireWire Target Disk Mode from the Open Firmware ok prompt too (after all, holding down T is just a snag key shortcut). This is useful for showing a little more information about what's going on; it shows debugging messages while starting up and while the other system is connected. The magic incantation is dev /firewire-disk-mode and then target-mode.

Yikes! No drives are showing up! No wonder Target Disk Mode didn't do anything!

I powered down the mini and removed the top case to ensure the interposer board was mated to the motherboard. It was. This could only mean the controller died and/or the logic board was shot, and the hard drive wasn't actually the culprit. Well, that's why we keep spares around! I had a spare G4 mini of the same speed with the drive cage from my dad's old system (new OEM optical drive and 120GB hard disk, both of which I installed for him back in the day); let's put the SSD in that system instead.

Transplanting the SSD from the old drive cage to the new one on the right and blowing dust out of every orifice on this one as well. I also replaced the PRAM battery while I was at it, since the voltage was measuring a little low.

Before packing up the old system for the parts bin, I wanted my CD back, but with a shot board the mini couldn't command the drive to eject it through software and unfortunately these drives don't have an eject hole. Instead, to get a disc out of most Panasonic UJ-series laptop drives, it's a matter of removing the top shell screws and taking off the cover, and the CD can then simply be popped off the spindle. The drive is defective anyway so I didn't bother reassembling it since it'll just go to the recyclers'.

That's more like it! Notice that, having manually started Target Disk Mode from the Open Firmware prompt, we have a little debugging log on the left half of the screen. The iBook G4 was able to partition and format the drive successfully.

Finally starting NetBSD/macppc 9.0 from the CD, since we've now got a working optical drive "for free" and we might as well upgrade the OS since we're reinstalling it. The system is back up and running.

This was an unexpected fault, and while a logic board failure on a 15-year-old computer is certainly not unheard of I wouldn't ordinarily think the board would fail before a spinning disk would. It's probably just bad luck, but there is one thing I chose to do differently with it: for this unit, as an experiment in longevity, I was using the Intel Core 2 Duo mini's 110W power supply because it has the same connector and same voltages but requires less of its capacity than the G4's 85W stock supply. I don't know if doing so had anything to do with it or not, but now that its power usage is even lower than the 21W it typically pulled before (down to just 15W), I put the original 85W supply back in service.

Overall, I think it might have been better to call this endeavour a Replacement Weekend, since it's now got a replacement logic board, a new SSD and a new-ish optical drive. It's still good to have the system back up and running, but now I think I'd like to find another spare.


  1. 15 years is 3 times longer than my 1.25GHz G4 mini, so congratulations.

    Mine apparently died of a logic board failure - mind you, the local Apple store "genius" came to the same conclusion even though his entire diagnostic process involved trying a different power cable! I got the impression logic board failures were not unusual and declined the offer of a reduced-price replacement board, getting a few weeks later one of the last old-shape Core 2 Duos that's still running 11 years later.

    The hard drive is still in use, running OpenBSD on an ancient Intel server box.

    1. Interesting. Well, let's hope this one lasts a little longer than that!


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