Ever wondered what goes on inside one of these?
This one was in the bottom of a box of Dublo spares that I acquired some time ago and the rivets had already been drilled out and replaced with nuts & bolts. It didn't work and the rubber cables were quite badly degraded, so time to take a peek inside and see what makes that delightful noise when you overload an A3!
There's a lot crammed in here!
Top left is the transformer. The incoming mains cable connects straight into the transformer coil.
The transformer has two coils, one feeds straight to the ac outlet on the back, the other goes through the rectifier (bottom, centre) and then into the regulator (bottom, right)
The coil on the top, right is the overload protection system and the source of the wonderful sound when it overloads.
Quite a simple design, when too much current builds up in the coil, it lifts the arm underneath. There are contacts below which open when the arm lifts, and this illuminates the warning lamp. When the power is cut, the current falls and the arm drops, closing the contact again.
Closer look at the rectifier, interference capacitor and power regulator...
And that's what goes on inside. This one has a faulty transformer - I applied 15v ac to the input of the rectifier and the regulator and overload operate as they should.
Potentially I could fit a replacement power supply and fit a mains cable with a moulded plug.
A future project to modernise the A3 maybe...
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