Bun's Lab – Telegram
Bun's Lab
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Electronics projects, vintæg computing, programming and repairs. A minimalist blog of sorts.
@BunsGarden @BunsNook
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The difference a 287 makes
15 min repair: llämp. Power transistors were fine, so were the diodes and the driver transistor. In the end it was a broken primary on the output transformer, luckily right at the connection.
If you know you know.

These are in Macintosh II, leak and destroy those computers. This particular one destroyed a IIfx.
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Ok I'm bummed out now. My 286 broke. This one:
Three out of three dead octek boards with Headland chipset. Although I think on this it's a mechanical issue. It broke after handling it to try the 287.
Bun's Lab
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HT12.pdf
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I don't believe it. There is actually a datasheet for this chipset.
I found out what killed the 286. A floating protective earth. Same issue as in the kitchen
Lovely
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Next thing on the bench: another 286 board.
I've already replaced a bunch of 74F244 buffers and 74F245 bi-directional bus transcievers because they had wonky looking outputs or even inputs
For example, this 244. The inputs looked like this, they were fed by the chipset part next to it, but also branched off to the 373 octal D flip flop above it.