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Sega Dreamcast Clock Battery Replacement

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Sega Dreamcast controller port board KATANA SUB BD 2 KAI
North American controller-port board (KATANA SUB BD 2 KAI). The clock cell BT1 is the blue cell at the left, with R1 beside it and a + mark at its left end (photo: Evan-Amos, public domain)

The Sega Dreamcast keeps its date and time in the real-time clock inside the AICA sound chip, held up by a rechargeable lithium coin cell, BT1, soldered to the controller-port board (Sega's sub board 2). The console charges the cell whenever it is switched on; Sega's US manual says the first charge takes about two hours and a charged cell keeps the date and time for about 20 days.[1][2] After twenty-odd years the cells no longer hold a charge, and the replacement is to desolder the old cell and fit a rechargeable ML-series cell, usually in a holder so the next change needs no soldering.[3]

Symptoms

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  • The date and time screen appears every time the console is switched on.[1]
  • Sega's own check: leave the console switched on for at least two hours. If the date and time screen still appears at the next power-on after that, the cell is no longer holding a charge.[1] See Sega Dreamcast Troubleshooting Guide.

A beep at power-on is a different fault: it comes from a VMU with flat cells in a controller, not from the clock cell.[4]

Safety

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Warning: the power supply at the left of the console runs from mains, and its primary reservoir capacitor can hold a charge after the console is unplugged.[5] Unplug the console before opening it.

Sega's caution for the clock cell is to replace it only with the same or an equivalent type recommended by the manufacturer.[6] The circuit charges the cell through R1, so a non-rechargeable CR2032 should not go in its place; Cameron Kaiser and dreamcast.wiki both use a rechargeable ML cell.[2][7][3] See Battery Refurbishment and Battery Explosion, Capacitor or Corrosion Damage.

Tools and parts

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  • Phillips screwdriver and a nylon spudger.[7]
  • Soldering iron, solder, and desoldering braid or a pump.
  • Multimeter.
  • A rechargeable cell and, if wanted, a holder (see the table).
Cells for BT1
Cell Capacity Size (diameter × height) Sega part for BT1 Notes
ML2020 45 mAh 20 × 2 mm 401-0067 (Panasonic ML2020/G1B) The usual stock cell
ML2032 65 mAh 20 × 3.2 mm 401-0066 (Hitachi ML2032T26) dreamcast.wiki's recommended replacement, in a vertical 2032 holder
ML2430 100 mAh 24.5 × 3.0 mm 401-0068 (Sanyo ML2430-VS1) Fitted to some consoles; may be too large for a vertical holder
LIR2032 3.6 to 3.7 V lithium-ion Not recommended: the console does not charge it fully

Capacities, sizes and the LIR2032 note from dreamcast.wiki; Sega part numbers from the EU service manual.[3][8]

dreamcast.wiki notes that a standard vertical 2032 holder has the same footprint as the stock soldered-in cell, and Kaiser found holder kits on sale that match the holes on the controller board "almost exactly".[3][7]

Procedure

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Remove the controller-port board

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Sega Dreamcast VA1 disassembly step 7 (Sega)
Sega's step 7: the top case lifted off. The controller-port board runs along the front edge of the base

The steps are the same as in Sega Dreamcast Controller Port Fuse Replacement, which shows Sega's photographs beside them.

  1. Unplug every lead, remove any disc and close the lid.[9]
  2. Turn the console over, remove the modem and the four screws (one in the modem bay, three in the corners).[10][7]
  3. Holding the top cover on, turn the console upright and lift the cover off.[9][10]
  4. Disconnect the flat cable from the main board, remove the four screws holding the controller-port board, and unplug the fan lead from CN4.[10]
  5. Ease the board out of the front shell and its clasps with a nylon spudger.[7]

Replace the cell

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  1. Note which way round the old cell sits, and the + mark printed beside BT1 on the board (visible in the lead photograph).
  2. On Kaiser's board the cell and its holder were soldered through the board at three points, with the apex of the triangle under a blob of lacquer. Heat each joint in turn and pull the old cell and holder out.[7]
  3. Clear the holes, or leave the solder in them to reuse for the new holder, as Kaiser did.[7]
  4. Fit the new holder in the same orientation as the old cell and solder it.[7]
  5. Fit the ML cell in the holder, observing the holder's polarity marking.
  6. Check the voltage across the holder's pins. Kaiser read about 3 V between the apex pin (negative) and the right-hand of the other two (positive).[7]

dreamcast.nu fitted a non-rechargeable CR2032 instead, and added a 1N4007 diode at R1 so that the console could not charge it.[11] The page shows the diode only in a photograph and does not give its orientation, and the change departs from Sega's same-type caution; the rechargeable ML route above needs no change to the circuit.[6]

Reassemble

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  1. Seat the board in the front shell and refit its four screws.[7][10]
  2. Plug the fan lead into CN4.[10]
  3. Push the flat cable squarely home. Kaiser bent a contact on this cable so that pins 1 and 2 touched, and the console misbehaved until he straightened it.[7]
  4. Refit the top case, the four base screws and the modem.[10]

Testing

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  1. Switch on, set the date and time, and leave the console on for about two hours to charge the cell.[1]
  2. Switch off and unplug for a while, then switch on again. The date and time should be kept, and the setting screen should not appear.[1][7]
  3. If the console now shuts down a few seconds after power-on, the fan lead or the flat cable is not seated properly.[7]

Revision notes

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Sega's parts list gives three alternative cells for BT1, all rechargeable ML types of different sizes, so the stock cell varies between consoles.[8] Kaiser's North American console had an ML2020; the North American KATANA SUB BD 2 KAI board in the lead photograph has a larger cell lying flat, and dreamcast.wiki records soldered-in ML2430 cells on some consoles.[7][3] Check which cell and footprint your board has before buying a holder. Sega's schematic and parts list are for the European sub board 2, 839-1124.[2]

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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 Sega, Dreamcast instruction manual (US, 2000), p. 12, "Rechargeable battery": charged whenever the Dreamcast is connected to power and switched on, including during play; charge for about two hours the first time; date and time kept for about 20 days after a two-hour charge; contact Sega if the battery does not retain a charge. Scanned at archive.org.
  2. ↑ 2.0 2.1 2.2 Sega Enterprises, Ltd., Service Manual: Dreamcast EU, No. 022-EU, October 1999, p. 8-25, schematic of KATANA SUB BD 2, part 839-1124: BT1 between ground and R1 (13 Ω 1 W), R1 fed from CN3 pin 2 (B.VCC); fan connector CN4; F1 in the controller-port 5 V feed. Hosted on this wiki as File:Sega Dreamcast EU Service Manual 022-EU.pdf.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 dreamcast.wiki, "Battery replacement", retrieved 2026-10-25. Stock cell a soldered-in ML2020, or on some consoles a larger soldered-in ML2430; replace with a holder and a rechargeable ML cell; ML2020 45 mAh 20 × 2 mm, ML2032 65 mAh 20 × 3.2 mm, ML2430 100 mAh 24.5 × 3.0 mm; LIR2032 cells (3.6 to 3.7 V) not recommended because the console does not charge them fully; ML2430 may be too large for a vertical holder; standard vertical 2032 holders fit the stock footprint; ML2032 recommended.
  4. ↑ Wikipedia, "VMU", retrieved 2026-10-01: a VMU with flat cells still works as a memory card but beeps when the Dreamcast is switched on.
  5. ↑ Power supply schematic marked "COD. SEGA 837-13570", hosted on this wiki as File:Sega Dreamcast Power Supply Schematic.pdf: bulk capacitor C3 68 µF 400 V.
  6. ↑ 6.0 6.1 Sega Enterprises, Service Manual: Dreamcast EU, No. 022-EU, p. 2-1, "Cautions To Be Observed": lithium battery replacement, "Replace only with the same or equivalent type recommended by the manufacturer"; laser precautions.
  7. ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 7.12 7.13 Cameron Kaiser, "Refurb weekend: Sega Dreamcast", Old Vintage Computing Research, November 2022. Four case screws (one in the expansion bay, three recessed in the corners); the controller board held by four screws, two at the side and two in the middle, and freed from the front shell and clasps with a nylon spudger; original cell an ML2020 with a lavender rim, fixed to a holder soldered through the board at three points, the apex of the triangle under a blob of lacquer; replaced with an ML2032 in a new holder in the same orientation; about 3 V between the apex (negative) and the right-hand of the other two points (positive); a regular CR2032 cannot be used; shutdown a few seconds after power-on caused by the flat cable or the fan connector; a bent flat-cable contact shorting pins 1 and 2.
  8. ↑ 8.0 8.1 Sega Enterprises, Service Manual: Dreamcast EU, No. 022-EU, p. 13-10, accessories list for sub board 2: BT1 401-0066 "BATTERY ML2032T26 HITACHI", 401-0067 "BATTERY ML2020/G1B PANASONIC", 401-0068 "BATTERY ML2430-VS1 SANYO"; R1 472-0130 "RES 13 OHM 1W 5%".
  9. ↑ 9.0 9.1 GDEMU, "GDEMU installation", retrieved 2026-10-25: disconnect all cables, remove the disc and close the lid; hold the top cover on while turning the console upright, because it holds down part of the GD-ROM assembly.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 Sega Enterprises, Service Manual: Dreamcast EU, No. 022-EU, pp. 5-1 to 5-3, "Disassembly Procedure VA1", steps 2 to 7 (case) and 14 to 17 (flat cable, four screws, fan connector CN4, sub PCB).
  11. ↑ dreamcast.nu, "How to fix a Dreamcast controller port not working", retrieved 2026-10-25: CR2032 holder and a 1N4007 diode soldered at the resistor so that no charging current reaches the battery, shown only in a photograph.
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