Bringing a Chain Printer Back to Life: The Power Supply [Hackaday]

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[Usagi Electric] has his Centurion minicomputer (and a few others) running like a top.  One feature that’s missing, though, is the ability to produce a hard copy. Now, a serious machine like the Centurion demands a serious printer. The answer to that is an ODEC-manufactured printer dressed in proper Centurion blue. This is no ordinary desktop printer, though. It’s a roughly 175lb (80 Kg) beast capable of printing 100 lines per minute. Each line is 132 characters wide, printed on the tractor-feed green bar paper we all associate with old computer systems.

This sort of printer was commonly known as a chain printer, as the letters are on a chain that rides over a series of 66 hammers. Logic on this printer is 74 series logic chips – no custom silicon or LSI (Large Scale Integration) parts on this 47-year-old monster.

This is [Usagi’s] first time working on a printer, so he’s taking it slowly. This episode was all about bringing up the power supply. He started by disconnecting the supply from the rest of the printer, removing the dust, dirt, and mud dauber wasp nests. The supply itself is linear and included a couple of previous repairs, including a power resistor, which had been swapped for a much newer aluminum model.

The first problem [Usagi] encountered was bringing back the giant old electrolytic capacitors. He hooked them up to his bench supply and tested them. It took a bit of work, but all three caps came back to life. Reforming is a great way to save/reuse original capacitors in old equipment. Shotgunning the caps isn’t always the answer!

With the caps working, [Usagi] re-installed the supply but kept it disconnected from the rest of the machine. It came up with 5, 30, 10, and -12 volt rails. Of course, this is just the start of a much larger project, but we’re already hooked. We can’t wait to see this printer hammering away, even if it isn’t musical. Just make sure you have some hearing protection, [Usagi]!