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Daewoo CPC-300 Capacitor Replacement Guide

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Daewoo CPC-300 inside
Inside an ivory CPC-300: the supply board at the left carries the two large reservoir capacitors

Daewoo's circuit diagrams for the Daewoo CPC-300 (Daewoo CPC-300 Schematics) include a capacitor list for the power regulator board and print values beside most electrolytics on the other sheets. The tables below collect them. The scan is low resolution, and a few designators in the capacitor list cannot be read; those rows are marked. The MSX Resource Center records at least three versions of the main board, so compare every value with the part on your board before ordering.[1]

Power regulator board (990A201200)

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Daewoo CPC-300 power supply schematic
Daewoo's sheet 1: the regulator board, with the capacitor list at the bottom centre

Daewoo's capacitor list on sheet 1 gives the type and a low-ESR remark for the supply electrolytics. The diagram itself labels the reservoirs of the ±12 V regulators.[2]

CPC-300 supply board electrolytics (Daewoo sheet 1)
Ref Value Voltage Type (Daewoo) Position
C1 2200 µF 35 V FWF, low ESR +5 V input reservoir after the bridge
C2 2200 µF 35 V FWF, low ESR +5 V input reservoir after the bridge
C3 220 µF 25 V RUF, low ESR L4960 input, after L1
C9 2.2 µF 50 V RUF, low ESR L4960 circuit
(not legible) 220 µF 10 V low ESR +5 V side
(not legible) 220 µF 10 V low ESR +5 V side
(not legible) 100 µF 16 V +5 V side
C15 1000 µF 35 V RS +12 V regulator input
C16 470 µF 35 V RS −12 V regulator input
C19 100 µF 16 V RS +12 V regulator output
C20 100 µF 16 V RS −12 V regulator output

The +5 V rail comes from a switching regulator, so C3 and the output capacitors work at its switching frequency, and Daewoo specified low-ESR parts for them and for C1 and C2. Fit low-ESR replacements of at least the same voltage. On the diagram the polarised capacitors on the +5 V output are C10 and C11, beside VR1, and C13, after the choke L3; match the three illegible rows to them by reading the parts on your board.[2]

Non-electrolytic parts on the same board: C5 2200 pF 50 V film, C7 0.033 µF 50 V film and C8 470 pF 50 V ceramic in the L4960 circuit, and two 0.1 µF 1000 V capacitors in the mains filter assembly.[2]

Main board

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CPC-300 main board electrolytics printed on the schematics
Ref Value Voltage Sheet Position
C16, C17, C18 22 µF 25 V 2 Supply input filters after L1 to L3 (+5 V, +12 V, −12 V)
C20 100 µF 16 V 3 Reset circuit
C21 47 µF 16 V 5 Joystick port +5 V
C15 10 µF 16 V 6 NE555 reset timer (IC38)
C12, C13, C14 10 µF 16 V 6 Sound mixing (PPI, slots, PSG)
C11 100 µF 16 V 7 +5 V to the RGB output stage
C2, C3 and a third 470 µF 10 V 7 RGB output coupling

[3]

Video board (990A201400)

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CPC-300 video board electrolytics (Daewoo sheet 7)
Ref Value Voltage Position
C13 100 µF 16 V +12 V input
C15 100 µF 16 V MC1377P supply
C3, C4, C5 22 µF 16 V RGB inputs to the MC1377P
C9 100 µF 16 V Video output stage
C11 100 µF 16 V Video output stage
C12 470 µF 10 V Video output stage
C25, C26 10 µF 16 V Sound output

[4] The RTC battery is under this board on the main board.[5] Check it for leakage whenever the video board is lifted; see Battery Explosion, Capacitor or Corrosion Damage.

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 the decoupling capacitors unless there is a reason.[6] On the CPC-300:

  1. The supply board: C1, C2, C3, the three +5 V output capacitors, C15, C16, C19 and C20.
  2. The video board, if the composite or RF picture is poor or noisy.
  3. The RGB coupling capacitors on the main board, if the RGB picture is dark or smeared.
  4. The rest only if they show damage.

Procedure

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Warning: the supply board's input side and the mains filter carry mains voltage when the machine is plugged in. Unplug it and discharge C1, C2, C15 and C16 before working on the board.

  1. Open the case as described in the Daewoo CPC-300 General Maintenance guide.
  2. Photograph the supply board and note the wiring to the transformer, the voltage selector and CN1.
  3. Read each capacitor's printed value before removing it, and compare it with the tables above.
  4. Replace one capacitor at a time, with the stripe on the same side.[6]
  5. Refit the regulators to the heatsink with fresh thermal compound if they had to be removed.

After the recap

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Measure the rails at the logic board test points TP1 (+5 V), TP2 (+12 V) and TP3 (−12 V) against TP4, or at cartridge slot pins 45, 48 and 50 against pin 41.[7] Then check the RGB, composite and RF pictures and the sound. Remaining faults are covered in the Daewoo CPC-300 Troubleshooting Guide.

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References

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  1. ↑ Daewoo CPC-300E, MSX Resource Center wiki—link(accessed 2026-10-21) The CPC-300E has the same motherboard as the CPC-300, of which there are at least three versions.
  2. ↑ 2.0 2.1 2.2 Daewoo, CPC-300 (domestic) schematics, sheet 1, power regulator assembly 990A201200. Capacitor list (No., capacitance, working voltage, type, remark): C1 2200 µF 35 V FWF low-ESR; C2 as C1; C3 220 µF 25 V RUF low-ESR and low impedance; C5 2200 pF 50 V film, non-inductive; C7 0.033 µF 50 V film; C8 470 pF 50 V ceramic; C9 2.2 µF 50 V RUF low-ESR and low impedance; then two rows of 220 µF 10 V and one of 100 µF 16 V whose designators cannot be read in the scan. Diagram: C1 and C2 after the RB-401 bridge D1 on the 11.5 V winding; C3 after the input choke L1 of the L4960 (IC1); C10, C11 and C13 at the regulator output and after the output choke L3; C15 1000 µF 35 V RS at the input of the KIA78012AP (IC2); C16 470 µF 35 V RS at the input of the 7912 (IC3); C19 and C20 marked "100µ ×2 16V RS" at the regulator outputs; C17, C18, C21 and C22 0.1 µF. Filter assembly 990A201300: C1 and C2 0.1 µF 1000 V DC MP. Hosted as File:Daewoo CPC-300 Schematics.pdf.
  3. ↑ Daewoo, CPC-300 (domestic) schematics: sheet 2 "Logic power", C16 to C18 22 µF ×3 25 V; sheet 3 "CPU interface", C20 100 µF 16 V in the reset circuit; sheet 5 "PSG, printer", C21 47 µF 16 V on the joystick port supply; sheet 6, C15 10 µF 16 V at the NE555 (IC38), C12, C13 and C14 10 µF 16 V in the sound mixing; sheet 7, logic assembly, C11 100 µF 16 V on +5 V and 470 µF 10 V coupling capacitors (C2, C3 and one more) on the RGB outputs. See Daewoo CPC-300 Schematics.
  4. ↑ Daewoo, CPC-300 (domestic) schematics, sheet 7, video assembly 990A201400: C13 100 µF 16 V at the +12 V input; C15 100 µF 16 V on the MC1377P supply; C3, C4 and C5 22 µF ×3 16 V on the R, G and B inputs; C9 100 µF 16 V, C11 100 µF 16 V and C12 470 µF 10 V in the output stage of Q1 and Q2; C25 and C26 10 µF ×2 16 V on the sound output. Further small capacitors in the output stage are not legible. See Daewoo CPC-300 Schematics.
  5. ↑ Daewoo CPC-300, MSX Resource Center wiki, 4 June 2026—link(accessed 2026-10-21) The RTC batteries are located under the composite video board and should be checked.
  6. ↑ 6.0 6.1 Recap recommendations, June 2018—link(accessed 2026-10-21) Reply by RetroTechie, 23 June 2018: supply bypass electrolytics round an MSX board can often be removed without the machine stopping; audio and video capacitors show their condition in the output; main power supply capacitors are worth replacing whatever their condition; use Rubycon, Chemi-Con, Nichicon or Panasonic parts from an established distributor; replace one at a time.
  7. ↑ Daewoo, CPC-300 (domestic) schematics, sheet 2: test points TP1 +5 V, TP2 +12 V, TP3 −12 V, TP4 ground. Sheet 8: cartridge slot pins 41 and 43 GND, 45 and 47 +5 V, 48 +12 V, 50 −12 V. See Daewoo CPC-300 Schematics.


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