Here is a complete set of images for the MC34063A that I just captured. The subject PSU is installed in the same scope used to capture the waveforms and is the new PSU released by Owon. Because of the cramped conditions I had to use the long ground leads, and for some captures and additional 2" wire to connect the probe tip to some of the IC's pins. However, the probe cables are equipped with ferrite cores which should counteract some of the effect of the long ground leads. On all captures CH1 is attached to pin 2 of the MC (Switch Emitter) and is used as the trigger source. CH2 was used to view the signals on all the other pins. In most cases there is a capture using DC coupling, so that the voltage levels can be read, and one or more captures using AC coupling to show a more detailed image of noise and spikes. There are also captures with CH2 connected to pin 4 of the adapter cable (-7.6V to adapter).
#1 - Shows the relationship between pin 2 and the timing capacitor.
#2 - Shows the voltage at the IC end of the current sense resistor. The voltage during pin 2 low is 8.4V, and ramps down about 200mV when pin 2 is high. If this voltage reaches 330mV it shortens the duty cycle to prevent damage. However, as can be seen, this doesn't happen during normal operation.
#3 & 4 - Shows the 8.4V as it appears on pin 6 of the MC.
#5 thru 7 - Shows the 7.6V as it appears on pin 4 of the MC. This is before it's filtered by L3 and EC9.
#8 & 9 - Shows the 7.6V as it appears on pin 4 of the PSU to adapter cable, adapter side of the cable.
#10 thru 13 - Shows the relationship between pin 2 and the COMP input. This pin is very sensitive and as can be seen, probing it alters the operation of the MC IC.
#14 thru 17 - Shows that the operation of the MC IC is altered even when just a 2" piece of wire is attached to the COMP pin. I fear that this extreme sensitivity can spell trouble if there is a high level of EMI nearby even if nothing is attached to this pin.