Editing Sinclair ZX Spectrum +2 (section)

== Power supply ==

Like the 128, the +2 takes an external unregulated supply and generates its own rails on board: a '''7805''' produces +5 V, and an inverter around transistors of the '''ZTX650/ZTX213''' family — the same arrangement used on the 48K Spectrum — produces ±12 V, here used for the RS232 drivers rather than for RAM — the 128 Service Manual puts the video, sound and UHF modulators on the +5 V rail.<ref name="tyne" /><ref name="sm128">''ZX Spectrum 128 Service Manual'', Sinclair Research Ltd. Hosted on this wiki as [[Sinclair ZX Spectrum 128 Service Manual]] ([[:File:ZX Spectrum 128 Service Manual.pdf|PDF]]). Source for section 1.10, the on-board power supply description, the rails and their loads, the expansion-connector supplies, the clock frequencies and the basic-checks procedure. The grey +2 is functionally a repackaged Spectrum 128.</ref>

The 128's on-board supply derives:<ref name="sm128" />

* '''+5 V''' from the 7805.
* '''+12 V''' from the TR4/TR5 inverter, rectified and smoothed by D15/C44.
* '''−12 V''' from a charge pump (C111/C112, D28/D29) off the same square wave.
* '''−5 V''' from the −12 V rail via zener D19, for the expansion port.

A working +2 draws roughly '''800 mA to 1.2 A''' depending on the type of RAM fitted, which makes a current-limited bench supply a useful diagnostic aid.<ref name="tyne" />