Repairing/understanding audio activated effects light (Schematic Inside) - Page 1
Forum section: electronics / repair

author: Peeps
author_rank: Contributor
timestamp: June 18, 2021, 08:59:46 am
content: I have this "DJ effects light" model Topaz 250 and was totally dead when plugged in. I took it apart and it consists of two boards, a power supply for the 250W tungsten light, and a smaller second board which powers a servo motor when activated by the audio picked up by an internal microphone. The power supply had a blown resistor which I replaced and it works fine.The smaller control board has a microphone attached to it which came loose at some point and contacted the chassis. Since the mic is floating around mains voltage, it caused zener diode ZD1 and ZD2 to physically explode as well as charring the microphone. I replaced the mic, ZD1 and ZD2, replaced the original HA17358 op-amp with an LM358.I didn't know the values of the original zeners so I used 10V a piece. It looks like the zeners are part of the voltage regulation for the IC and set the voltage across it while being supplied by capacitive dropper C9.My issue is it just doesn't work and I can't wrap my head around this op-amp circuit they have here. Also the output of pin 7 is maxed at Vcc (20V) yet the triac isn't even conducting. Could anyone shed some light on this circuit for me?

author: Renate
author_rank: Super Contributor
timestamp: June 18, 2021, 02:57:11 pm
content: Once you start mixing up AC referenced suppplies and crazy grounds and 1/2 references, names get confusing.So we'll stick with yours."+V" is right off the line, in some ways this is not a supply."Gnd" is rectified off the neutral, in some ways this is your supply.The output of the 2nd op amp is "20V", I suppose this means it is "+V".Because the gate of the triac is reference to "+V" there has to be a voltage from "+V"When the opcode goes negative, then you have gate drive.Right now, you have no gate drive and the light should stay off.This is best trouble shot with an isolation transformer.DVM or analog meter would work easily too.Probably the mic opamp is blown sky high.It feeds through two diodes as peak detector to the second opamp.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: June 18, 2021, 08:02:38 pm
content: Is the mic you replaced the same as the original?(looks like this is an Electret Condensor circuit)

author: Peeps
author_rank: Contributor
timestamp: June 21, 2021, 01:31:52 am
content: Quote from: Renate on June 18, 2021, 02:57:11 pmGood suggestion on the isolation transformer. I recently converted a large step-up transformer to isolation but wasn't using it because I am a fool. During testing, the microphone touched the chassis and made a nice explosive spark show in front of my faceI had also replaced the op-amp when I replaced the zeners but to no avail.Quote from: Audiorepair on June 18, 2021, 08:02:38 pmSo this is one of my concerns. It is an electret condensor but has no markings. The resistance measured 2.2k so I replaced it with the one below. My knowledge on these is next to nothing but I was hoping that they're fairly interchangeable.https://www.digikey.ca/en/products/detail/pui-audio-inc/AOM-4546L-R/1745494