Amiga 4000 · rev B

Before you start

• Before the capacitors, the battery. Rev B has a 3.6 V rechargeable NiCd battery (BT176) ^[1][2], which leaks with age. The liquid eats the traces and vias around it, reaches the mouse and joystick ports and the clock area, and hides under chips that look intact ^[9]. If yours is still there, remove it as soon as possible or bring the machine to the shop so we can replace it and treat the corrosion.
• The A4000's power supply is internal. Always work with the power cable unplugged from the mains, and don't open the power supply: the 230 V side is not something to work on at home. This list covers the main board only.
• Nineteen of the 21 are SMD electrolytics, and those are the ones that leak. On the A4000 the worst is usually the audio area: the electrolyte gets into the vias under the chips, where no cleaning product can reach, and the chips often have to be lifted to clean it ^[9]. The electrolyte is almost transparent and conductive, so a board that looks new may already be damaged ^[10].
• Work with hot air or two irons and don't force the SMD parts off: on an already corroded board the pad can come away stuck to the capacitor. Clean off the residue thoroughly and inspect the traces before soldering in the new ones, and observe the polarity of each one.
• The replacement's voltage can be the same as the original or higher, never lower. Commodore used 16 V on the 22 µF ones and 6.3 V on the 100 µF one ^[1]; the Amiga-Wiki asks for 25 V and 16 V ^[3], which is fine, if it fits in the same space.
• The map is for rev B. On amigapcb.org rev 2, one of the first production boards, has the same electrolytics in the same places ^[2]. The "cost reduced" rev D (A4000-CR) is a different board, with the 68030 and the Chip RAM soldered on ^[7][8], and the Amiga-Wiki gives it a different count (seven 22 µF and a single 470 µF) ^[3]: don't use this map on it. For rev C, which is rare, we found no data.
• Not on the map: C406H, a 100 µF position that is left empty from the factory ^[1][2][3]; the axial electrolytics on the Zorro slot daughterboard, three 220 µF and two 22 µF, all 16 V ^[1][3]; and the four 22 µF 16 V SMD ones on the A3630 processor board ^[1]. If you find broken traces or damaged chips, bring the board to the shop.