Getting Started: Checking for Magic Smoke

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“A boot disk, a boot disk! My kingdom for a boot disk!” – me(just now)

Upon returning from the location of your first vintage find, you’ll be buzzing with joy. Or buzzing with anxiety. Or buzzing with concern over why your significant other has not only chose to fund this parade float into your past, but has insisted that you document the voyage with pictures and stories for the world to share (I swear she’s up to something, but I just can’t focus when she smiles like that). There’s an awful lot of buzzing at your kitchen table, and you haven’t even plugged in the little grey box.

Hopefully the buzzing is kept to a minimum. As a delightfully brilliant and candid Kanuckastani enginerd (I say with the utmost respect) will tell you, in an attempt to see if it will chooch, you grab a hundred and twenty wall pixies and shove them into a machine that ain’t been runnin for a decade or more and you run the risk of breaking something and letting out all the magic smoke that makes ‘er go. Loosely translated, that’s shop talk for what often happens when these things spend a goodly amount of time as wall flowers and skimping out on some much needed lovin’.

No computer is designed nor built with the intent of being the perfect computer to satisfy all the users’ needs. There is no end all be all for anybody. It’s a shame and a sad truth, but there it is. The delicate nature of the little components inside that box is only amplified by time. A quick look around the web and into the forums and you see that as we approach 20 and 30 year marks for these, the same issues pop up. Fortunately for us, we began with this Macintosh Classic model, so we can do a little bit more troubleshooting than usual with the built in OS. Like May West said to the electrician, “Let’s plug it in and see if we get a short!”

Fortunately, the angry pixies are still successimg_1091fully contained in their little homes, and the magic smoke remains inside with them. It’s not all good news, however. The POST process should result in two things: A happy Mac, and a startup tone. The startup tone on the Macintosh Classic is not any version of the iconic chimes associated with Macintosh for over 30 years. It’s a simple tone, but it’s missing. Not the worst thing to have, but it’s often a harbinger of greater dangers. Obviously we need to crack open the case. This brings us to the first tool that may be outside the realm of your typical household tool kit: a 6″ extended T15 screwdriver bit.

Cracking into the case is fairly straight forward, 2 x T15 screws at the bottom near the IO and another 2 coarser pitched T15s (don’t confuse the two) at the top deep inside the handle.

If you don’t have the extension, I’m at a loss for what can fit deep in there. Like stylish jeans, there isn’t much room where you need it most. Now that you have the screws loose you can separate the two halves of the case keeping in mind that the weight is all in the screen end of things. I would be remiss if I didn’t mention that you are now exposed to some high voltage potentials. If you have had this machine plugged into the wall for any period of time within the last couple months, the capacitors in the analogue board may still have enough charge to hurt your feelings.

img_1095Now that it’s in its alltogethers not all together, you can see the logic board sitting in its slot at the back of the chassis. In order to get this free, there are three cables and a card that need to be removed. There in a slot at the back of the machine, sticking out like a bank manager’s key card, is the expandable RAM card. Without this, your Macintosh Classic will be limited to 1MB of RAM and nearly useless for all but the simplest of applications running in Mac OS 6 or earlier. Wanna hear something super neat?! I forgot to mention that when I was playing around in the desktop on the first boot, I decided to get a good look at the system profile and see if there was anything worth noting there. SPOILER ALERT: there wasn’t. Well, there was a single item that was img_1050-1.jpgoff. I mean, it’s great that the hard disk is still worthy of spinning after all these years, but the Total Memory is being reported as 512k!!! This is no good at all. Even if there had been a boot chime, THIS is enough reason to crack the case and do some troubleshooting.

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Here are the next three obstacles in your path. The floppy, SCSI, and power cables will all need to disconnect. AGAIN, I WARN YOU: Please be careful near the neck of the tube. In addition to being super delicate, they can continue to be very hostile if the large capacitors are still holding a charge. That’s not to say that the angry pixies will come out and look for you, but if you aren’t very mindful of the placement of your meaty paws, you’ll get quite a bite. Take this seriously and don’t rush. I would recommend removing the floppy first since it’s the most open. Grab close to the connector and rock back and forth gently. The SCSI connector is next (if you have a HDD installed) and you can apply the same technique. The connectors on these are img_1098slightly more secure than other types, so if you attempt to pull the cable itself (as near to the connector as possible), you’ll have less catastrophic failure than others. When that’s free, the last piece is the power connector. Looking like a mutant ATX connector, this guy has a single catch that can almost never move out of the way enough. Be mindful of your surroundings. Stay in the moment. When you’ve freed this last bit of cable, you can feel the main logic almost heave itself out of its slot. Gently lift this and set it next to you on the bench in order to bask in the brilliance of mechanical logistics. This is also a good time to point out that this will never be your main computer as you’ll be constantly wanting to look up all the markings you find under the hood.

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Even if you aren’t recording your adventure, take some time to prop your board against something and just stare for a while.

Now that the logical components are out of the box, take a good look around. On this main logic board there are eight electrolytic capacitors. While none of these seem to be leaking (they literally look like they’ve puked on themselves if they do), they don’t have the typical relief scoring on their tops. That means that if they should ever wear down and decide to die, they’ll likely pop and spray their guts instead of just a simple leak. Make some notes of these values and head over to your favorite parts store for some replacements. I like tantalums, but that’s a conversation for next time. Another time bomb is that PRAM battery in the bottom left. It’s dated 1991. Anything over five years will require replacement. Get that old can out of there. It’s a disaster when they go…

While looking around, take note of the main CPU. The battle hardened Motorola 68000 running at a spirited 8 MHz. Having spares of anything couldn’t hurt in this hobby. Neither does it hurt to make lots of notes of what you find. Even a blog or a personal wiki can serve you well. Note the large can-like capacitors and their values and orientations. The area surrounding them should be clean and shiny. Anything that looks like paste or rust needs to be attacked with isopropyl alcohol and cotton swabs as fast as you find it. Since this machine has a peculiar memory issue, it’s also worth looking at memory controlling components while we’re here. The installed 1MB of RAM chips all look fine so this likely to be an issue with an IC or a VIA. It’s also possible that the expansion card is faulty. Let’s see about that.

img_1103-1.jpgThe expansion card has two slots for a pair of 30 pin SIMMs. I would recommend they match. Even in other brands of machines, the 30 pin SIMMs tend to be fussy about playing well with others. Make sure they match speed, size, even brand. This card has eight 256 megabit ICs totaling 1 megabyte, just like on the board. I’m going to try my hardest to find another pair of eight chip SIMMs to bring this machine to its full 4 MB of memory. Inspection of this item is also critical because of how system resources are shared. All the solder joints look solid and all the traces appear to be clean. I img_1104-1may eventually run an iron over the card connector, but I’ll wait and see how the rest of the restore happens to go. Of note: make sure you have a proper jumper on your card. The end opposite the main connector is a set of pins with (hopefully) a jumper. This allows the card to act as either a single 1 MB card OR have even more installed in the open slots. In the event you are missing this jumper, pins can be soldered together, so don’t loose a lot of sleep over this. It is a different size than most disk drive jumpers, though. I wouldn’t risk forcing something that doesn’t fit too well.

In the next article, I intend to give this logic board a good bath, there will be some parts to order, the soldering iron will need to make its debut, and finally, the remainder of the machine will need to be separated into its major components to address some corrosion prevention. Have you had some trouble getting into your machines? Is there a tool you’re fond of using that can make tear-downs more efficient? What forum have you found to have the most helpful members? Leave a comment below and share a story.

This is Ty; logging off.

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