Schematic for MK114


I am quite experienced in electronics and have built this kit. With other Velleman kits, there has been a Schematic in the bottom right corner of the manual, but not the MK114. I have looked in the download sections of the US and UK Velleman websites, but not found any PDFs with a Schematic.

The reason I need the Schematic is that the lamp is always on whether or not a speaker connection is connected. I downloaded a datasheet for IC1: … /4N35.html

From looking at the PCB I found out that the base of the phototransistor side (pin 6 on the datasheet) of the chip is open circuit on the PCB. I connected a 470K resistor between pin 4 and 6 of the chip and the circuit works reasonably OK now, but not perfectly.

Could you provide a Schematic diagram (PM or email it me maybe) so I can diagnose the problem properly.

When I get the circuit working properly with a bulb, I plan to connect the output to a Schmitt trigger / push button de-bounce circuit (that I’ll design and build my self on strip board) to provide an Analogue to Digital conversion for the pulsed 12V trigger input of a strobe light.


Diagram can be found here: