Diagnosing the Unico Model 24D "Rocket"
Diagnosing the Unico Model 24D "Rocket"
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David Smith 2022
"It's broken..."
"It's broken..."
My friend brought over his old and trusty fence charger as it was no longer working. I made no promises, but we opened it up to see what we'd find. It looked pretty simple, but I was very cautious with 5000-10,000V and a hefty current output. Here's what we found.
Outside & Inside Views
Outside & Inside Views
Unico Model 24D "Rocket"
Unico Model 24D "Rocket"
Love the period graphics;
worth it to investigate just for the visual history.
Love the period graphics;
worth it to investigate just for the visual history.
Original certification
Original certification
Still hanging on... barely
Still hanging on... barely
Rear Panel
Rear Panel
No, it wasn't the fuse.
Note the wing nut is the
ground connection
Confirmed "Vintage"
Confirmed "Vintage"
Date of manufacture stamped inside
Cycling Thermal Switch
Cycling Thermal Switch
The socket (not visible from this bottom view) is a thermal switch; auto-cycles about every two seconds with a not-quite-50% duty cycle.
The Key Ingredient
The Key Ingredient
The 60Hz AC step-up transformer generates 5-10kV according to the 'net. The spark we drew at the end suggests that's about right.
Bad bulb :(
Bad bulb :(
After checking everything else, I decided to change the (definitely bad looking) NE-2 neon bulb, which I happened to have a drawer of.
Obvious difference side-by-side
Obvious difference side-by-side
Maybe it would at least light up if I changed the bulb.
That... fixed it?!
That... fixed it?!
It did, and turns out it was on the HV secondary side, and was shorting the output. (Who'd have thought the pilot light was the cause of the failure.)
Circuit Sketch
Note the neon pilot light
across the output.
Circuit Sketch
Note the neon pilot light
across the output.
Back in business (maybe for another 50 years)
Back in business (maybe for another 50 years)
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