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128k - new addition to the fleet


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A couple months ago I picked up a non-operating 128k, it only made a ticking noise when powered on.  I started doing a bunch of searching online and ran across the YouTube videos put together by forum member @JDW, many of you are probably familiar with him as he is a frequent contributor.  I reached out to James directly and he ended up helping enormously with the revival of this machine.  We did a bunch of troubleshooting of individual components, and swapping components with my 512k to check parts that could not easily be tested individually.  We made multiple rounds of semi-progress, and after we had ruled out many of the more specialized individual components that could cause problems, we took the shotgun approach and replaced all the analog board capacitors and some usual-suspect diodes.  After the full recap I flipped the power switch expecting the worst, but instead I got the startup-bong, and no magic smoke!  The 400k drive wouldn't take a disk, it wouldn't "drop down", so I followed the instructions in JDW's 400k drive cleaning and lubrication video, and now it works great.

 

For those of you unfamiliar with JDW's YouTube videos, they are probably the best instructional YouTube videos I have ever seen on any topic, electronics or otherwise.  He shows the process from the very beginning steps all the way through completion and testing, with great camera work in 4k, covering every tiny detail.  He also links to all the tools/supplies used in the videos, and when applicable provides links to a Mouser cart with the necessary parts.

 

I also owe a big thanks to @Dog Cow for sending me the 400k System 4.1 boot disk shown in the photos below.

 

128k.thumb.jpg.5f735712a71fc285d3eae9eff40b58db.jpg986286139_128kFinder4.1.thumb.jpg.6de7f93a5a092cf730447e586845972e.jpg

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2 hours ago, bibilit said:

Any information concerning faulty diodes ?

 

Diode CR5 had failed, so I replaced that along with transistor Q3 since they fail together.  I tested diodes CR20 and CR21, the readings for CR20 were a bit off, I went ahead and replaced CR20 and CR21 since I had them on hand.  As part of the shotgun approach I replaced the following diodes: CR1, CR15, CR18, CR19.  Additionally resistor R2 was visibly burned, so I replaced that as well.

 

There are a number of parts that Larry Pina suggests be upgraded on these boards.  Based on your post count I suspect you're familiar with Larry's books - Dead Mac Scrolls, and Macintosh Repair & Upgrade Secrets.  Larry lists a bunch of parts which should be upgraded, and JDW put together a spreadsheet containing the modern versions of all these parts with Mouser part numbers.  Here is the link from his128k recap video info: https://bit.ly/3diHUUG.  The spreadsheet has three tabs.  I ended up replacing all the "upgrade" parts from the first tab, and all the electrolytic capacitors as well.

 

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2 hours ago, joshc said:

Very clean example, what are your plans for it? Do you have a HD-20 to use with it?

Thanks!  No HD-20, and there probably isn't one in the cards unless I happen to run across one.  My plan is to get a Floppy Emu since I can use that with my other compact Macs as well.

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To reiterate what I said in our email dialog, I would once again like to say you are to be commended on bringing that machine back to life, @JC8080!  I did offer some advice, but you got your hands dirty and maintained the determination and passion to get the job done.  You also did a lot of leg-work by reading through the Larry Pina repair books which helped, and having that second machine from which to swap components was also extremely helpful too.  All said... Great work!  

 

I actually have a working HD20, but despite that, I too highly recommend the FloppyEMU. It's the main reason why I've never purchased a SCSI2SD.  FloppyEMU just works well enough for my needs and is something I can connect and reconnect externally, moving it from my Mac512 to SE/30 with ease.  Adding new software is fairly ease by putting the SD card into a modern Mac and arranging disk images as necessary in Mini vMac (e.g., sometimes images on Macintosh Garden need tweaks in order to become bootable).  It's really the single best purchase for these old compact Macs.

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Saw this on reddit (u/gf99b... mentioned I didn't see it) and decided to also chime in here. That machine is in immaculate condition and you did a pretty good job at getting it working again.

 

As for the FloppyEmu, I highly recommend getting one to anyone who owns a vintage Mac. While you won't be able to use the hard drive (HD-20) emulation mode with the 128k, you can still use it in floppy emulation mode with 400k images. Makes it very convenient for copying files and software from the internet (Macintosh Garden, etc.) to your vintage Mac(s).

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I finally broke down and bought the Floppy Emu today.  I'd been thinking about it for a while, but now that I have 3 working machines I figured it would be nice to actually get software on them.  My SE has a working hard drive, but that could change at any moment.  Since I have a 512k and now at 128k it makes sense to get the Floppy Emu since the SCSI2SD won't work with either.  The SCSI2SD seems like a nice setup to leave installed permanently in a single machine.  I may end up doing that for one of my other machines in the future, but the Floppy Emu seems like a great gadget since you can easily move it from one machine to another.

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To sum up, no, you can’t really run an HD20 (or FloppyEmu in HD20 mode) on a stock 128k.  There isn’t enough room to load HFS into RAM and still have a functional machine.  @Dog Cow did some nice research on it here https://macgui.com/news/article.php?t=500 but I at least (and apparently a few others) haven’t been able to get this to work on a physical 128k (you can see notes on my attempt on that page), and anyway his suggestion is just a fun hack that’s not really practical to run anything beyond TeachText.  

 

As noted in the thread @JDW linked (I agree on the fine quality of his videos, by the way!), you can run an HD20 on a 128k if you upgrade it to Mac Plus ROMs (i.e. create a “128kE”), which is easy to do.  I believe, though, this will also effectively reduce your RAM size a bit, as the 128k ROM does a few things that take up extra system heap space.

 

Also, that’s a nice looking 128k up there, well done!

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