Editing BBC Master Compact (section)

=== Disc unit and power supply ===

The disc unit holds a 3.5-inch drive, a mains power supply board and space for a second drive. Its back carries the mains switch, a mains outlet for the monitor, the fuse and the mains input, and the 5&nbsp;V lead to the keyboard unit comes out through a strain-relief grommet.<ref name="chrisc" /><ref name="smcms">Acorn Computers, ''[[BBC Master Compact Service Manual|Master Series Compact Microcomputer Service Manual]]'', 0458,002, section 2, Master Compact monitor stand service guide, PDF pp. 50–58: safety tests (earth continuity under 0.1 Ω, 1.5 kV AC insulation test for ten seconds); first-line servicing only, with Acorn telling users and dealers not to fault-find on the power supply; dismantling; the 5 A plug fuse; mains switch, auxiliary output and input; mains fuse anti-surge 3.15 A HBC 250 V (type T); changing the supply board (four screws, mains input, DC output and earth tag); a second supply type with different cable layout; the +5 V lead, part of the DC cable assembly, under 100 mΩ per wire at full load; the disc data cable; replacing the drive (Sony F6 3W, set as drive 0); the second-drive upgrade.</ref> Acorn's manual says the supply can come in more than one type with the same voltages; repairers on stardot report at least two.<ref name="smcms" /><ref name="sd30613">stardot.org.uk, [https://stardot.org.uk/forums/viewtopic.php?t=30613 "Refurb process for Master Compact Base Unit PSU"] (February–March 2025, retrieved 2026-10-02). egel: at least two types of Compact base unit supply. 1024MAK: renew the RIFA X2 capacitor and the small primary-side start-up electrolytic; on his supply C1 is 0.1 µF 275 V AC class X2 and C10 is 220 µF 10 V (he fitted 220 µF 16 V 105 °C). 1980s_john: a cracked RIFA and a bulging output electrolytic replaced on his Compact. Secondary source.</ref> The supply is marked 5&nbsp;V 2&nbsp;A, and owners run the keyboard unit from any regulated 5&nbsp;V supply of 2&nbsp;A or more with a centre-positive plug.<ref name="sd26390">stardot.org.uk, [https://stardot.org.uk/forums/viewtopic.php?t=26390 "BBC Master Compact Power Supply?"] (February–March 2023, retrieved 2026-10-02). 1024MAK: a 2 A regulated 5 V supply is enough; egel: the original supply is printed 5V 2A; jgharston: he uses a mains adaptor rated 5 V 2.5 A, body 0 V and tip +5 V. Secondary source.</ref>