Daewoo CPC-300 General Maintenance
The Daewoo CPC-300 is a Korean MSX2 computer from 1986 with its power supply built into the case.[1] Daewoo's own circuit diagrams survive and are hosted as Daewoo CPC-300 Schematics; no service manual with disassembly or adjustment procedures has surfaced. The checks below come from those diagrams, the MSX Resource Center and photographs of opened machines.
Mains supply
[edit | edit source]- The label gives 100 V/220 V, 60 Hz and 21 W.[2] Daewoo's diagram shows a voltage select switch on the transformer primary with 220 V and 100 V positions.[3] Check the selector setting before connecting the machine to mains.
- The mains fuse is in the filter assembly; the diagram marks it "250T 0.5A".[3] Replace it with the same rating.
Warning: the filter assembly, the voltage selector, the transformer primary and the input side of the supply board carry mains voltage whenever the machine is plugged in. Unplug it before opening the case, and discharge the large capacitors on the supply board before working on it.
Opening the case
[edit | edit source]No disassembly procedure has been published. In the photographed machine the top of the case folds back from the base. The cartridge slot is fixed in the top half and joined to the main board by ribbon cables.[4] The reset switch and power LED are on a separate reset key assembly (990A201700), joined to the main board by a connector.[5]
- Unplug the mains lead and every other cable, and remove any cartridge.
- Photograph the underside before removing any screw, so the screw positions can be matched on reassembly.
- Remove the screws that hold the two halves together and lift the top half slowly from the front.
- Fold the top back without straining the ribbon cables to the cartridge slot, or unplug them, noting their orientation.
The clock battery
[edit | edit source]The CPC-300 keeps its clock in an RP5C01 backed by a 3 V battery.[6] The MSX Resource Center notes that the batteries are under the composite video board and should be checked on any machine bought.[1] Lift the video board, inspect the cells and the board under them, and remove a leaking cell at once. See Battery Explosion, Capacitor or Corrosion Damage for cleaning up after a leak.
Measuring the supply
[edit | edit source]The logic board has test points for the three rails, and the cartridge slot carries them too.[7][6]
| Rail | Test point | Cartridge slot pin |
|---|---|---|
| +5 V | TP1 | 45, 47 |
| +12 V | TP2 | 48 |
| −12 V | TP3 | 50 |
| Ground | TP4 | 41, 43 |
Daewoo's diagrams give no tolerance. On the diagram a preset, VR1 (471), sits in the feedback network of the L4960 that makes +5 V. Leave it alone unless +5 V is clearly out of range.[3]
Connectors and controls
[edit | edit source]The rear panel has the expansion bus, the printer port, a colour or monochrome switch, the RGB socket, video and sound outputs, and the RF output with a channel 3 or 4 switch.[8] If the picture is black and white, check that the colour or monochrome switch (SW2 on the video board) is set to colour before looking for a fault.[9] Clean cartridge, printer and joystick contacts with isopropyl alcohol.
Capacitors
[edit | edit source]Daewoo's capacitor list for the supply board, and the values printed on the other sheets, are collected in the Daewoo CPC-300 Capacitor Replacement Guide. Advice on the MSX Resource Center forum is to replace the main supply's capacitors whatever their condition and to judge the others by the picture and sound.[10]
Related pages
[edit | edit source]- Daewoo CPC-300
- Daewoo CPC-300 Troubleshooting Guide
- Daewoo CPC-300 Capacitor Replacement Guide
- Daewoo CPC-300 Schematics
- Recommended Tools
References
[edit | edit source]- ↑ 1.0 1.1 Daewoo CPC-300, MSX Resource Center wiki, 4 June 2026—link(accessed 2026-10-21) Korean MSX2 from 1986; power supply built in; RTC batteries located under the composite video board, to be checked on any machine bought; main RAM in slot 0-2; MSX-TUTOR firmware skipped with SELECT or disabled with SET SYSTEM 1; reset button and light pen connector.
- ↑ Rating label of a Daewoo CPC-300 (File:Daewoo CPC-300 rating label.jpg, uploaded to the MSX Resource Center wiki by Mars2000you on 18 June 2020): MODEL NO.: CPC-300, rated voltage 100V/220V, 60Hz, rated power consumption 21W; stickers 1987.11 and REV.D.
- ↑ 3.0 3.1 3.2 Daewoo, CPC-300 (domestic) schematics, sheet 1: AC input, power switch, filter assembly 990A201300 (fuse marked "250T 0.5A", line filters LF1 and LF2 of 1 mH, capacitors C1 and C2 of 0.1 µF 1000 V DC), voltage select switch (220 V and 100 V), transformer with 11.5 V and 16 V secondaries; power regulator assembly 990A201200: RB-401 bridge (D1), L4960 (IC1) with VR1 (471), L2 (150 µH), D2 (BY398) and L3 (1 mH) for +5 V; 1N4002 diodes D3 to D6, KIA78012AP (IC2) for +12 V and a 7912 (IC3) for −12 V; output connector CN1: red +5 V, yellow +12 V, green −12 V, black ground. Hosted as File:Daewoo CPC-300 Schematics.pdf; see Daewoo CPC-300 Schematics.
- ↑ Photograph of the inside of an ivory CPC-300, uploaded to the MSX Resource Center wiki by Mars2000you on 4 February 2016 (File:Daewoo CPC-300 inside.jpg): top of the case folded back, with the cartridge slot in the top half wired to the main board by ribbon cables; transformer and supply board at the left with two large electrolytic capacitors, a finned heatsink over the regulators, a toroidal inductor and a line filter LF-300; video board at the top centre; main board marked MSX Version 2.
- ↑ Daewoo, CPC-300 (domestic) schematics, sheet 3 "CPU interface": reset key assembly 990A201700 with the reset switch and the power LED, joined to the main board by a connector; reset circuit with C20 (100 µF, 16 V). See Daewoo CPC-300 Schematics.
- ↑ 6.0 6.1 Daewoo, CPC-300 (domestic) schematics, sheet 8 "RTC, slot interface": RP5C01 (IC15) with a 3 V battery on its supply; cartridge slot connector pins 41 and 43 GND, 45 and 47 +5 V, 48 +12 V, 50 −12 V, 49 sound input. See Daewoo CPC-300 Schematics.
- ↑ Daewoo, CPC-300 (domestic) schematics, sheet 2 "Logic power": supply input CN15 (+5 V, +12 V, −12 V, ground) through chokes L1 and L2 (39 µH) and L3 (100 µH) with C16, C17 and C18 (22 µF, 25 V) and C28 to C30 (0.1 µF); test points TP1 +5 V, TP2 +12 V, TP3 −12 V, TP4 ground. See Daewoo CPC-300 Schematics.
- ↑ Photograph of the rear panel of a black CPC-300, uploaded to the MSX Resource Center wiki by Gdx on 16 December 2015 (File:Daewoo CPC-300 rear connectors.jpg): EXPANSION BUS, PRINTER, MONITOR COLOR/MONO switch, RGB, VIDEO, SOUND, CH 3/4 switch, RF.
- ↑ Daewoo, CPC-300 (domestic) schematics, sheet 7 "Video": video assembly 990A201400 with an MC1377P encoder, colour or monochrome switch SW2, channel switch SW1, video and sound jacks and the RF modulator; RGB output drivers on the logic board. See Daewoo CPC-300 Schematics.
- ↑ 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; replace one at a time.
