Getting Started: Reading Between the Trace Lines

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Something something ESD safety…I forget…zzz

The current state of operations is a little scary, to be honest. The Macintosh Classic is on the bench in pieces. The case is yellow, the keyboard and mouse are sticky, the screen is a slightly “off” shape, and most worrisome is that even the built-in 1MB of RAM isn’t reporting correctly in the system report. Since this is all about making sure the hobby is approachable and bares as few costs as possible to eek out maximum performance, I’m going to chase down this memory issue first.

The best part of digging into vintage computing is the luxury of hindsight and documentation. Service manuals are no longer hidden behind costly manufacturer support programs. Magazine editors have weighed in with their respective feedback on performance. But the most valuable component to any part of the restoration process is the community. The Macintosh started its life with the loving embrace of local Mac User Groups (MUG). Today, there are few, but the online forums and blogs pick up much of what’s been lost.

With a quick search for “Macintosh Classic RAM Problem”, plenty of pages of users reports will fill the screen. What’s super interesting is that this situation (no matter how much RAM is installed, the same 512k is being reported) is mentioned SEVERAL times! If you don’t have an account at the 68k Macintosh Liberation Army, get one! This place is full of fantastic people from every background. The stories they share span from anecdotes during the time these machines were young to the electronic necromancy that is how to develop modern software and hardware to support them for a long time.

One user (macalle69) mentions the problem with RAM. If you take a look at the thread, there’s the system report with only 512k visible to Finder. More importantly, the first comment is another user (marcelv) who has taken some nice photos of how he approached this problem as if it were nothing more than standard maintenance. Now it’s time to study the pictures and buy some tools.

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Pin 1 is at the white dot on the top left and the pins are numbered counter-clockwise (anti-clockwise).

Looking at the diagram and the attached photos, it’s easy to find the assumed culprit at UH6. According to the thread, there’s good reason to believe the vias (the passages through the board that connect all the layers) have degraded. On first inspection, it doesn’t appear that is the case, BUT there’s potential for the vias to have hidden damage. The whole point of picking this computer above all other models as a starting block is the low cost of entry. Reflowing solder into some vias is peanuts compared to tracking down new chips. That may still need to be done, but let’s do the easy and cheap thing before moving on.

First tool of the day is a soldering iron. I could write whole posts on which to buy and how to use them. I recommend that you take a look at somebody like Dave Jones at the EEVblog for a thorough detailing on what makes a good iron worth using. His expertise diminishes most others in the world of electronics science media. All I can say is that you should have your budget tell you what you can do. For my purposes, which involve spending as little as possible in case I feel like tossing this whole lot into the trash bin when I’m finished, the simplest will serve me just fine.

I do not recommend anybody ever use those hyper-tempting butane fed soldering irons from “great” names. They’ve been known to work in the field…in a pinch, but my experience has been dicey at best. They’ve not got enough thermal capacity to withstand outdoor winds, they make a very distracting noise when used inside, burning out a tip requires you to buy a whole kit to replace it. I still have two. I still avoid using either. I will turn to Amazon for something more realistic. This model is Chinese and comes in as many varieties as you can imagine. Drop shipments ftw? The most important parts of this model are the adjustable temperature and the standard sized tips.

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What you save on the iron you can spend on consumables!

You now have the preferred chisel tip, some tweezers, a case, de-soldering wick…and a light duty 60W soldering iron to do some learning. And please learn if you haven’t. I’ve been butting wires together for decades, but I still have a hard time with simple stuff like making assumptions about which end is hot (https://ameriburn.org/public-resources/find-a-burn-center/). Some of these Chinese models even come with a bag or box to keep everything so that it’s all neatly organized and contained for when you put it out for the trash collector. If you stick with this, move on to something higher quality. If you give up, don’t loose sleep over spending less than $20 on some funny stories about how you got those new scars on your hands.

The next item you’ll need is a hobby knife, but what a great excuse to buy a kit of tools that includes a hobby knife?! I personally use an older model of precision tool kit from iFixit. It’s no longer available, but I believe there are others from the same manufactures. The new model is quite comprehensive also, even though it’s a bit more costly. In the end, any kind of scratchy pokey will be fine as long as you can control it safely.

Now it’s possible to gingerly scrape away the solder mask from the traces between the 4 and 10 pins and their associated via. Not too rough. It’s still a thin bit of copper

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Give it a poke…just the tip…

Underneath the green mask. If you do go too deep and break the trace, a bit of “bodge wire” can be used to jump from the pin to the via. You know that drawer of broken USB power cables you’ve been collecting in a drawer for something? Well your wife does and it’s driving her bonkers. This is a source of bodge wire. Keep plenty of it around. It will come in handy more often than Batman’s utility belt.

With the traces bare, it’s possible to flux and solder over the newly scored path from pin to via. You can just sort of blob it on there. Be mindful of the proximity to the other pins, vias, and traces nearby. This would be a terrible time to make an accidental short. Give everything a good alcohol cleaning, and plug in this little green time machine!

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This is the point in the process where you get to crack open your favorite brand of libation and rejoice! I mean…not rejoice in success. Get that idea out of your head. You are now able to navigate a soldering iron and you’ve learned how to interface with some substrate, but this was in no way a success. You see, if your Macintosh Classic is anything like mine, you’ll reinstall the board and boot to desktop to find that it’s still only reporting 512k! Might as well be 512L cause this thing isn’t going anywhere near a full word processor. Get those digital dreams of Office 3 out of your head. This poor thing is just as useless as it’s (then) 8 year old predecessor. AND THAT’S A LOT OF USELESS!

But your tool bag has some new tools. And your hand has a few new burns providing some much needed character. And your kitchen table probably has some matching scars, too. If you think it doesn’t, ask your wife. She’ll be happy to show you where they’re hiding.

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It’s not the end of the world. You’ve only just got done with the easiest bullet on the checklist. That’s like getting ready for a 10k race and putting on your shoes just to decide that it’s just too much effort to do more than clumsily knot your laces. And I don’t blame you! This is frustrating and you have to learn everything by feel! But it does get better. The next item to check on this list is the actual memory control chips. The one seen today is called a “flip-flop”. So that sounds fun. At less than a dollar, it’s going to get replaced. This is cheaper than buying a multi-meter, and SMD soldering with a $12 Chinese iron is a skill everybody should know. Are you following along with your own project? Do you even read this far? Is there a source for used tools in your area that you would recommend? Leave a comment below and share a story.

This is Ty; logging off.

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