Editing Acorn 6502 Second Processor (section)

== Power supply ==

[[File:Acorn 6502 Second Processor with cover removed.jpg|thumb|right|200px|Transformer and power supply board at the front, main board behind (photo: Chris Whytehead, CC BY-SA 3.0)]]

The supply is a linear regulator on its own board beside the mains transformer. Acorn rates it at 216 to 264 V AC, 47 to 63 Hz, 14 W, and 1 A maximum at +5 V.<ref name="sm" /> Its circuit (service manual p. 35) is a centre-tapped transformer T1 with Schottky rectifiers D1 and D2 (11DQ04), a 4700 µF 16 V reservoir C1, a TIP42 pass transistor TR1 driven by TR3 and TR4 (BC182) with a 3.9 V zener reference, a 100 ohm trimmer VR1 marked "set 5V", a 47 µF 35 V output capacitor C5 and a 1 A output fuse F1.<ref name="sm" />

The main board has its own protection: a 2 A fuse FS1, and a thyristor TH1 triggered through a BZY88C 5.1 V zener (D2) that shorts the supply and blows FS1 if the voltage rises too far.<ref name="sm" /><ref name="cct" /> A blown FS1 therefore means either a short on the board or a supply giving too high a voltage.

Section 2 of the service manual gives the rear panel fuse as T315mA, while the case parts list gives a 20 × 5 mm 1 A fuse. The moulded mains plug takes a 3 A fuse.<ref name="sm" /> Check what is fitted before replacing it.

Warning: the transformer primary and the rear fuse holder carry mains voltage. Unplug the unit before removing the lid.