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Daewoo CPC-400 Capacitor Replacement Guide

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Daewoo CPC-400 main board
CPC-400 main board; two larger electrolytics stand beside the connector at the right-hand edge

No capacitor list, parts list or supply circuit for the Daewoo CPC-400 (X-II) has been published. Daewoo's user manual has no circuit diagram,[1] and the main board schematic published by RBSC covers the logic, not the power supply. RBSC also found that the schematic gives some capacitor values incorrectly.[2] Read every value from the parts on your own board.

What is known

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  • The main board carries a few electrolytic capacitors, two of them larger ones beside the connector on its right-hand edge.[3]
  • The video board sits above the main board and carries the clock's AA cells. Leaking cells have corroded video boards badly enough that one needed extra capacitors after cleaning and resoldering.[2]
  • The power supply is built in and runs from 100 V or 220 V according to a rear selector.[1] No photograph of its board has been found.
  • The related CPC-300 has a published supply circuit and capacitor list. The two machines share the DW64MX1 gate array, but their supplies have not been shown to be the same, so check against the board before using any CPC-300 value.

Which to replace first

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Advice on the MSX Resource Center forum is to replace the main supply's capacitors whatever their condition, judge the audio and video capacitors by the picture and sound, and leave decoupling capacitors unless there is a reason.[4] On the CPC-400:

  1. The power supply's electrolytics.
  2. Any capacitor on the video board near the clock cells, after the board has been cleaned of leakage.
  3. The larger capacitors at the main board's supply connector.
  4. The rest only if they leak, bulge or a rail is noisy.

Recording the board

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  1. Remove the clock cells first, and deal with any leakage as described in Battery Explosion, Capacitor or Corrosion Damage.
  2. Photograph the supply, the video board and the main board from above, then each electrolytic close up.
  3. Write down each capacitor's designator, value, voltage, size and polarity.
  4. Order replacements of the same value and at least the same voltage.
Template for your own CPC-400 capacitor list
Ref Value Voltage Diameter × height Board Notes
Supply
Video
Main

Procedure

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Warning: the supply, the voltage selector and the rear auxiliary outlets carry mains voltage when the machine is plugged in. Unplug it and discharge the supply's large capacitors before working on them.

  1. Open the case as described in the Daewoo CPC-400 General Maintenance guide.
  2. Replace one capacitor at a time, with the stripe on the same side.[4]
  3. Clean any electrolyte and check the tracks round each large capacitor.
  4. Reassemble and check the cables between the video board and the main board for corrosion.

After the recap

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Measure the rails at the cartridge slot: +5 V on pins 45 and 47, +12 V on pin 48 and −12 V on pin 50, against pin 41.[1] Then check the picture on RGB and composite outputs, the sound, and both floppy drives. Remaining faults are covered in the Daewoo CPC-400 Troubleshooting Guide.

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References

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  1. ↑ 1.0 1.1 1.2 Daewoo, X-II (CPC-400/400S) user manual: a user's manual with no circuit diagram or parts list; printed page 235 gives the cartridge slot pins (41 and 43 GND, 45 and 47 +5 V, 48 +12 V, 50 −12 V); printed page 5 shows the rear panel with the voltage selector, auxiliary outlets and fuse. See Daewoo CPC-400 User Manual.
  2. ↑ 2.0 2.1 Daewoo CPC-400/400S MSX2/MSX2+ Conversion Project, RBSC, 2026—link(accessed 2026-10-21) Project description (Docs/Daewoo_CPC400_Upgrade_Project_English.pdf, pages 3 and 4): the main board's crystal oscillator ran unstably until its capacitors were chosen afresh, because the board schematic lists some capacitor values incorrectly; one video board, corroded by leaking clock cells, needed cleaning, resoldering and additional capacitors; the clock cells are AA cells on the video board above the main board. Mainboard/Schematics/X2PCB_Schematics.pdf: one-sheet logic schematic of the main board.
  3. ↑ Photograph of the CPC-400 main board, uploaded to the MSX Resource Center wiki by Gdx on 28 June 2016 (File:Daewoo CPC-400 main board.jpg): two larger radial electrolytic capacitors beside a white connector on the right-hand edge and several small electrolytics elsewhere; values not legible at the photograph's resolution.
  4. ↑ 4.0 4.1 Recap recommendations, June 2018—link(accessed 2026-10-21) Reply by RetroTechie, 23 June 2018: main power supply capacitors in an MSX are worth replacing whatever their condition; audio and video capacitors show their condition in the output; bypass capacitors round the board can often be removed without the machine stopping; replace one at a time to avoid mixing up values or polarity.


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