Apple 820-1156-A iMac G3 Down Converter Power Supply 400-700MHz G3 iMac

Apple 820-1156-A iMac G3 Down Converter Power Supply 400-700MHz G3 iMac

The Apple 820-1156-A is the internal down converter power supply board used in Apple iMac G3 all-in-one computers covering the 400–700MHz processor range. This board accepts the primary power from the iMac's main flyback power supply and converts it down to the regulated lower voltages required by the iMac G3's logic board, CRT, and peripheral subsystems. It is a custom Apple-proprietary PCB design, not an off-the-shelf ATX unit.

Specifications & What's Included

• Part Number: 820-1156-A (Apple Computer Inc.)
• Compatible Systems: Apple iMac G3, 400MHz through 700MHz models
• Board Type: Down Converter / Secondary Power Supply
• Form Factor: Internal board-mount (irregular/custom PCB shape)
• On-board components: toroidal power inductor, multiple electrolytic capacitors, transformer, MOSFETs, heat shield bracket (rear)
• Output connector: 4-pin JST-style board connector visible on PCB
• Multi-pin edge connector on right side for logic board interface
• PCB copyright: Apple Computer Inc. © 2000
• Includes: Power supply board only — no enclosure, cables, or additional accessories

Applications

The iMac G3 (1998–2003) was Apple's landmark consumer all-in-one desktop, built around the PowerPC G3 processor and recognizable for its translucent colored plastic enclosure. The 820-1156-A down converter board is a service/repair part for iMac G3 units in the 400–700MHz range — models spanning the Slot Loading Fruit Colors, Snow, and early Summer 2000 through 2001 revisions. This board is most commonly needed when an iMac G3 fails to power on or exhibits unstable secondary voltages, as the down converter is a common failure point separate from the main flyback supply. It is used today primarily by vintage Mac collectors, independent repair technicians, and institutions maintaining older Apple hardware for display or legacy use.