Need help understanding PNP Base into NPN Collecter circuit for LED Array
Oh, it's simple, you think the circuit provided is the ground control for the leds. It is not. It is the high side control for the leds. Your breadboard is not accurate reflection of the circuit. The PNP is turning on, and you are essentially shorting out the leds with 5V on both sides.







simulate this circuit &ndash; Schematic created using CircuitLab

So, when the red wire, 5V is connected to the emitter, and the PNP is ON, the 5V is connected to the collector and you short out the leds. When you remove it, I'm taking an educated guess, you create a ground path from the collector through the base of the TIP 42C, which in turn goes through the NPN that is turned on. This could have damaged the TIP 42C you are testing with, btw. Floating emitter isn't ideal.

In the cube, they are using the 2n2222 (or 2n3904 on the board layout) as npn drivers of the PNP TIP 42C. This controls the led anode. The low side is controlled by the ULN2803 darlington transistor array ICs on the shift register board. This is done to allow a scanning function to control that many leds from a small number of pins of the micro controller.


  FYI, each line from JP2 in the first picture is a ground line from a 64 LED array and the lines from the IC1 are driven by an arduino uno.


No, JP2 is the Anodes of the LED array.