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Just fixed my first dead power supply from 1985, night and day difference
So I cracked open this old Commodore 64 power supply someone dropped off at my shop last Tuesday. It was totally dead, no output at all. I figured it was just the usual capacitor aging but after poking around with my Fluke 117 I found the main switching transistor was shorted. Replaced that plus the startup cap and a resistor that was way out of spec. Plugged it in after 3 hours of work and it put out a clean 5V and 9V AC just like it should. Before the fix the ripple was garbage on the scope but now it's dead flat. Has anyone else run into bad switching transistors in older gear thats hard to source replacements for?
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stone.lisa23d ago
Man that's a solid fix. I've had a few Commodore and old Atari power bricks come through with the main switching transistor blown, and sourcing those TO-220 parts is a pain. Usually it's the older ST or Fairchild ones that are completely gone from every distributor I check. Had to pull a 2SC3150 from a dead monitor once just to get a known good one. Getting a clean flat trace on the scope after all that work is a great feeling though. You spent real time on it and it paid off.
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the_anthony23d ago
Those older Fairchild parts are getting scarce but I've had better luck cross-referencing the original part number against old Motorola databooks from the 80s. Found a direct sub for a 2SC3150 in a 1987 RF transistor guide that none of the modern distributors even list.
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quinna8923d ago
Gotta ask though, is finding a 30+ year old Motorola databook really easier than just throwing a modern equivalent in there? I mean, plenty of generic RF transistors will do the job in most vintage gear without hunting down some obscure 1987 cross-reference. And honestly, most people running old Commodore bricks aren't pushing them to the limit anyway. Just sounds like a lot of extra work for something that probably works fine with a $2 generic part off Mouser. But hey, if you enjoy the treasure hunt, more power to you.
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