Disco lighting from the pre-DMX era – what lies inside the analogue Trix BrokenSwing 501?

Today we’re taking a look inside the Trix Broken Swing – a classic disco lighting effect that many of us may have enjoyed years ago in clubs. The nameplate immediately reveals a few interesting facts – the unit was manufactured in Slovakia, although it was imported by the Polish company Strong from Końskie.

The programme descriptions indicate the presence of two motors responsible for the movement or animation of the light. Interestingly, there is no DMX protocol here yet – the input is an analogue voltage signal of 0–10 V supplied via a jack socket. This was a very popular solution back then, before the digital standard came to dominate the market.

The unit has certainly seen a fair bit of use over the years, but its 320 W power consumption and hefty 11 kilograms’ weight still make quite an impression. So let’s take a look at the components used to build this rugged classic.

On the casing, there’s a telling Polish-language sticker warning that the power must be switched off when replacing the bulb, and that the glass itself must not be touched with bare fingers. As has rightly been pointed out, grease left on the bulb, combined with the extreme heat, poses a risk of explosion, so you need to be careful with your eyes.

At the front, we have the arrangement of angled mirrors characteristic of this model, along with a central, rotating prism fitted with dichroic filters. It is this assembly that is responsible for splitting and setting the main beam of light in motion, which gave the device its name (‘broken swing’). As you can see, one of the mirrors in my unit is cracked, which gives this name a very ironic, literal meaning.
Let’s take a look inside – simply remove the cover:

Once the metal plate has been removed, we’re greeted by a very open interior housed within an aluminium profile. On the left-hand side is a sturdy Sunon cooling fan and the main circuit board containing the electronics and microprocessor. In the centre, you can see one of the stepper motors driving the internal disc with the apertures. On the right-hand side, at the very end, there is a ceramic socket for a power-hungry 24V 250W halogen bulb, complete with a reflector. The powerful transformer required to power this unit is concealed underneath.

Visible on the board are, amongst other things, a microcontroller with a sticker covering the actual markings (probably some classic model with pre-loaded software), a quad operational amplifier LM324N (presumably for the audio circuit of the built-in microphone) and two well-known and popular L293D motor drivers. The stepper motor visible next to it is the KP4M2-203 model with a 1.8-step stroke, manufactured by the Indian company Tandon Motors.

The mystery of the device’s 11-kilogramme weight has been solved – hidden just beneath the main board is a gigantic, classic core transformer, whose main task is to power the power-hungry incandescent bulb. In the next shot, however, the second of the stepper motors is clearly visible, along with the fitted, contoured aperture disc and the ceramic holder itself.

Finally, a table from the documentation:

The lifespan of the light source – 50–300 hours – really surprised me.

To sum up, we have a transformer, a bit of electronics, a halogen bulb and two stepper motors, all cleverly packed into a robust aluminium profile. A simple, fully repairable and, in my opinion, rather charming design from the turn of the last century.
Have you come across this type of device, or perhaps even serviced them? What tended to go wrong with them most often? Apart from those bulbs...