I'm not sure if anyone will be able to help me out and I'm sorry to just burst in here. I'm new to the forum, so I'm hoping I'm not going to offend anyone.

As I approach retirement, I'm hoping to get a better understanding of electronics - really to 'close the loop' a bit on a hobby and interest I had from childhood.

When I was younger, I tinkered and built things - heck, I even managed some decent repairs. But I was always a bit weak on theory. That haunted me when I came up against my nemesis - a Pulsar ZERO 2250 sound to light controller mostly used by mobile DJs. These were commonly available in the 1980s, but a bit prone to failure. I was often presented with them, but never able to repair them myself.

They had a weird power-supply set up. Unlike the transformers and bridge rectifiers common at the time, these little babies dispensed with that bulky part and opted to connect the PCB to mains voltage (220v/110v). They make use of a zener diode, a large wire-wound resistor, and some low voltage electrolytes, and a couple of diodes.

But mentally, I just don't 'get it'.

I've attached the diagrams, does the way this work make sense to the more experienced people here? Is anyone able to explain it?

Thank you.
Riko

 

Do you have the other schematic pages you can post?
Where is the sound input?

 

Do you have the other schematic pages you can post?
Where is the sound input?

Yes, indeed. I've attached it here.

 

Is this a schematic that was 'reverse engineered' by someone or yourself?
Or a Manuf. published one?
Max.

 

That's from the manufacture, out of their archives about 10 years ago.

 

Yikes, directly connected into 110VAC. Probably plugged into a circuit with no GFCIs. Manual override switch tied to L. Spill some coffee on the board and hit the switch - DJ becomes part of the special effects. Great way to save a couple of bucks on a transformer. At least the audio input was isolated. Didn't look like it used earth ground, either.

 

A hand-drawn schematic from the manufacturer(?). It must be really a garage operation.

This is a dangerous design to troubleshoot, as the circuit board is directly connected to the mains.
You would need an isolation transformer to do any checking of waveforms with an oscilloscope

The circuit is a little convoluted and I'm not sure how it all exactly works, but here's my initial shot at that:

The audio signal in is isolated by the audio transformer from the mains voltages.
The transformer output is amplified by common-emitter amplifier P3 and then buffered by complimentary push-pull emitter follower transistors N3 and P4 to give a low impedance output to the following circuit (at the top of the Pg2).

This positive part of the audio waveform is rectified by D4 to drive transistor N2, and the negative part of the audio waveform is rectified by D3 to drive transistor P2.
The output of these two transistors is summed to drive transistor NH1 which triggers the TRIAC to turn on the lights in response to both the positive and negative peaks of the music.

The purpose of P1 and N1 is also not clear to me.
It may generate pulses at the power line frequency that helps synchronize the TRIAC music signal pulses to the line frequency.

 

Yeah, I was uncertain of why they needed ZC if they aren't doing phase control dimming. I bet this design goes back a lot farther than the 80s.