Switch Mode Power Supply from a SX-64

RE: Switch Mode Power Supply from a SX-64

mcb1 — Wed, 14 Feb 2018 22:02:51 GMT

Just another thought.

A lot of earlier supplies had 'crowbar' devices that would detect some abnormal condition and trip the fuse, etc.

Modern supplies tend to have better control IC's and can handle these events properly.

There are also a few capacitors to the frame ground.

It's possible that one of these could be faulty.

Mark

RE: Switch Mode Power Supply from a SX-64

mcb1 — Wed, 14 Feb 2018 21:57:38 GMT

A trick taught to me for fixing switchmode supplies ....

Feed the mains through a 100/150w mains lamp to the device.

If there is a fault, it will light the lamp, and usually not damage the surrounding components ... ie those explosions of sparks you see in the movies. [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-2a699b58-b4fb-453a-8afc-05a139fc6a61/contentimage_5F00_938.png:16:16]

Generally switchmode supplies will run happily without load, but some seem to rely on the load and it's filtering to smooth the voltage.

Nice to see these coming back to life.

My mother purchased one new way back, and then kept it.

My son now has it and it still works ... well last time he fired it up.

Mark

RE: Switch Mode Power Supply from a SX-64

genebren — Tue, 13 Feb 2018 19:08:07 GMT

Following up on Doug's comment above, one of the likely downstream shorts might be one of the large electrolytic capacitors. These are know to age and fail.

Gene

RE: Switch Mode Power Supply from a SX-64

dougw — Tue, 13 Feb 2018 18:47:25 GMT

That transistor would most likely fail short due to excessive current - due to a short or excessive load downstream.

RE: Switch Mode Power Supply from a SX-64

genebren — Tue, 13 Feb 2018 17:57:38 GMT

It would seem that finding a replacement power supply would be far easier, but maybe not a satisfying than fixing the original. Find a donor system with a working power supply, or just replace the supply with a modern supply with the same specifications. I have always looked the simplicity of some of the old technology. I have often thought about building copies of some of my most loved systems (mostly through emulation and/or FPGA implementations).

Enjoy your toys!

Gene