Power Circuit (ZX Spectrum 16/48k)

the zx spectrum 16/48k accepts 9v dc positive outer (inverted) power supply the 9v goes to parts of the system expected power draw the 9v input is expected to draw around 580ma when powered on and running in a working system a faulty z80 for example is known to draw about 800ma 800ma so significantly more obviously any components could fail and draw more or less power, but a working system typically pulls 580ma 5v rail the 9v is passed into a 7805 ldo regulator to generate the 5v rail 12v dc / 12v dc / 5v dc rails the remaining voltage rails are all generating from a circuit on the pcb the main components involved (and those that usually fail) are the coil, the transistors tr4 and tr5, and a bunch of diodes a quick spot to measure the voltages are below the 12v rail is not needed in order to get av output