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Another SE msytery

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April 21, 2019 at 09:40 #12915


Bought an SE FDHD (aka “superdrive”) … for parts. When it arrived I plugged it in and powered it up: Got a “bong” and the HD light lit as though it were trying to load the OS, but no video. I opened it up expecting to find a problem with the analog board but instead I found the CRT board was unplugged from the tube. I put it back and started over. This time I got a video display with the Mac / question-mark icon, so I stuck an 800k OS 6 startup disk in and booted up to 6.0.8. When I shut down the disk ejected, so things could be worse.

They were. Pulling apart further I found the battery had leaked and pried it out of the tray; a rusty mess. Testing the HD with an Adaptec SCSI controller on a Win/Linux system I found the drive would not be recognized by the controller. I wasn’t too surprised to find the HD dead; it was a Quantum from about 1990.

But I was surprised to find the battery hadn’t ruined the motherboard. Apparently the unit had been stored upside down, and when the battery leaked it leaked onto the steel carriage below (or above, if you’re upside down) the power supply. There was a large and ugly rusted spot on the carriage. I pulled the carriage out and soaked it in warm water and phosphoric acid.

The acid removed the rust but it also removed the grey matte coating that Apple puts on their carriages. I’ve seen it on several but didn’t know what was its purpose. Apparently it is there, in part at least, to prevent rust, because when I rinsed and dried the now-bare metal I saw traces of rust forming immediately.

So here’s the mystery: What was the coating, and what should I do to prevent further rust? I’m thinking a light coat of zinc primer. What say you?

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