After many years searching I finally got a working IQ8300 with a bonus of a boxed colour pack. No PSU, but since it's a ZX81 clone-esque with a 7805 regulator I checked the polarity and fed it 8v@1A and after a reset got a nice READY prompt on a composite monitor. Quick BASIC program entry and all is well.
Colour box is a different story though. I guessed that the flying lead was supposed to go into the Monitor socket since that's all it would reach (I hadn't RTFM at that point

Reading the forum I saw the specs of the real PSU and noted that the colour box needs more current for it to work. Upping the voltage to 12v doesn't help my bench PSU isn't breaking a sweat, running at 400mA. It's set to limit at 1A.
Am I going wrong anywhere? I've now RTFM and it says I should get a picture no matter what.
Cheers!