28 December 2018 by Ty
The last time the Macintosh Classic was running, it was reporting only 512k of RAM. The good news is that fixing the memory is a matter of removing and replacing components. The bad news is that she’ll never remember her name. Any suggestions are welcome. But first, it’s time to do some shopping!
In a previous article, I mentioned a reference to a potentially faulty IC involved with memory management. The flip-flop controller mentioned by marcelv is still available from various parts distributors. Mouser has this item cheap. Cheap enough, in fact, that I got the whole set of memory-related ICs. The thought is to replace one component and test before moving on to the next, but be prepared to replace the whole set if needed. After all, the cost is fairly low, and the process for remove and replace is much the same for each. Here is the list:
The Flip-Flop controller is the same controller that got attention when reworking the trace lines. When the memory report was the same after reflowing the vias and reinforcing the traces, the obvious next step is to replace the whole IC. Fire up the iron!
SMD soldering is not all that bad. There are so many ways to make the job easier. There are hot tweezers and hot air stations. There are IR heating tables. But, you have a $12 hot stick. Not a terrible tool with some practice and patience. It’s best to have a couple consumables on hand, though. Desoldering wick, proper solder, and flux are going to go a long way to ease you through this chore. Also, you may like to use some magnification, a spudger, a stand to hold the board, and tweezers in order to get a handle on things. If you don’t have these yet, follow these links.
- Black Stick Spudger
- Solder Pick
- Cross Lock Tweezers
- No Clean Flux Paste
- Clip-on Jewelers Loupe
- Isopropyl Alcohol (no link for this because it’s cheaper at your local mega-mart) Make sure it’s 91% or higher.
- PCB Stand
- Desoldering Wick
- Fine Solder
Make note of the alignment of the IC. Fit your iron with a chisel or a beveled tip. Lay a bit of flux on the pins, and flow some solder across those legs. After a couple trips across those pins with your best drag soldering techniques, you should be able to feel the chip slide off the pads. Extract that package and utilize the desoldering wick to clean up your mess. Don’t scrub, or you’ll likely lift a pad off the board as I have. Don’t worry if you do. Not every pin is utilized, so a test will be done to ensure efficacy.
Look at that! A full 1MB of RAM being reported. Well, since we have this case apart, and the iron is still hot, let’s just strike at those long in the tooth capacitors. Eight capacitors in total. You’ll need to find a single 1 uf and seven 47 uf capacitors. Mouser is great for this kind of thing, but if you’re making this hobby into a habit, I recommend finding a deal on bulk packages. If you want a kit with these items ready to go, keep an eye out on the main page for a new storefront with some supplies to enable your mission.
Working SMD capacitors is a pain, but not nearly as bad as working SMD ICs. Some others will recommend to just use side cutters and rip the parts from the substrate. The danger with this method is that you could potentially damage the substrate, and inevitably you will lift a pad. Take some time and flood out the pins. Extra thermal mass gives you a little extra time to jump back and forth to both sides till the capacitor slides off the pads. Clean up as you go. Isopropyl alcohol will help with any flux. That stuff is ironically corrosive. When it comes time to install the new caps, keep in mind that the new tantalum capacitors put a line on the positive side where the old electrolytics have the line on the negative side.
With all eight caps in place, first boot begins with a very cheery POST chime. While the case is still off, let’s make sure the memory issue is resolved completely by installing the RAM upgrade card along with a pair of 1 MB SIMMs. Make sure they are the same timing as the memory on the board; 120 ns.
The hardware is all functional, now! Time to make sure we can get the software under control. As I mentioned at the beginning, This particular Macintosh has a bootable disk image stored in ROM. For the un-initiated, the ROM of these 68k based machines holds a good deal of code to make sure all the parts of the OS can find all the hardware. Sometimes this is referred to as springboard code. Much like a PC-compatible has BIOS, the Macintosh ROM is the first bit of code to launch.
The Macintosh Classic has a ROM big enough to hold System 6.0.3 without needing to install or boot from floppy. In order to get access to this “hidden” disk image, boot the machine while holding down ⌘-option-X-O. “XO” is the code name for this machine, so it’s fitting. You can even select the Boot Disk from the Start Up control panel for persistent booting if yours has a hard disk installed. While this is a great place to start working on floppy based programs and documents, there’s nothing natively installed here to get a usable image on to the hard disk. And you cannot install anything to this secret enclave. While you may be able to get by, just like the first floppy based machines, I would recommend a storage solution as soon as possible. This, like many, has a 40MB SCSI hard disk installed. I’m going to push forward with a clean install. If you do not have storage in yours, stay tuned! We’ll eventually go to (SPOILER ALERT) a solid state solution.
Officially the Macintosh Classic supports installation of system 6.0.7 through System 7.5.5. If you have the means to locate some original install disks, RestoBytes recommends the “less is more” approach due to the small RAM ceiling. System 6.0.8 is a 2 disk set, and System 7.1 is a 6 disk set. Both of these have been released freely from Apple for distribution, so you can even download the installers and copy them to floppy if you have the equipment. But for right now, let’s pretend you have only what’s been covered in this series and you don’t want to pay eBay prices.
There are ways to get your fix in a reliable way. Several small shops that specialize in this sort of thing will offer “disk duplication” or “data migration” services that can build your own serviceable floppy disks. In fact, I want to reference a future addition to RestoBytes for exactly such a service. Before that goes live, though, I want to teach you how to do it all yourself. Do you have a recommendation for what to name this machine? If you are following along with your own model, do you have plans for upgrades or accessories that you want to try? Do you feel the ROM disk is a useful tool or a superfluous Easter egg? Leave a comment and share your story. Don’t forget to follow RestoBytes on Instagram for more from the lab.
This is Ty; logging off