Daewoo CPC-400 Troubleshooting Guide
No service manual for the Daewoo CPC-400 (X-II) has surfaced. The checks below use the owner's troubleshooting list and slot pinout in Daewoo's Korean user manual (Daewoo CPC-400 User Manual), the MSX Resource Center, and the faults RBSC found when it reworked CPC-400 and 400S boards in 2025 and 2026. For opening the case and the mains warning, see the Daewoo CPC-400 General Maintenance guide.
What a working machine shows
[edit | edit source]Daewoo's manual has the owner put a disk in drive A and press the power switch at the bottom right of the front. The first screen shows "X2 Bios version 1.00" and "128K Video memory installed". If a password has been set, a "Password:" prompt follows, and the manual gives a two-key combination, held while switching on, that skips a forgotten password.[1]
Start with the rails
[edit | edit source]| Measure between | Expect |
|---|---|
| Pin 45 or 47 and pin 41 | +5 V |
| Pin 48 and pin 41 | +12 V |
| Pin 50 and pin 41 | −12 V |
Symptoms
[edit | edit source]| Symptom | Check first | Notes |
|---|---|---|
| Nothing at all, power lamp off | Mains lead, voltage selector, the rear-panel fuse | The selector has 100 V and 220 V positions; the fuse is on the rear panel.[3] If a new fuse blows at once, look for a short in the supply before fitting another. |
| No picture after switching on | The monitor | Daewoo's list: check that the monitor is switched on and that its contrast and brightness are set.[4] |
| Only noise on the screen | The video lead, the power lamp, the cartridge | Check the display connection, that the power lamp is lit, and that any cartridge is fully inserted.[4] |
| Picture unclear, rolling or noisy | The monitor's adjustments and nearby equipment | Adjust the display's horizontal and vertical hold; move the machine away from sources of interference.[4] |
| Black-and-white picture | The colour/mono switch on the rear | Set it to colour.[3] |
| No sound | Audio lead, monitor volume, the stereo/mono switch | Daewoo's list gives the cable and volume.[4] In stereo the PSG's channel A comes out on the left only and channels B and C on the right, and B and C can sound quieter than A.[5] Check the switch position and both channels before suspecting the board. |
| Keys do nothing, cursor gone | Software crash | Daewoo's list: try the key combination that restores the cursor, then press RESET.[4] |
| Unstable running, random crashes | Mains sharing, then the board | Daewoo's list warns against sharing a socket with heaters and other heavy loads.[4] On a board RBSC reworked, two 74LS367 buffers were faulty.[6] |
| No start, no video, with a mixed set of boards | The master oscillator | On the CPC-400S the master oscillator is on the video board, and on the CPC-400 on the main board. RBSC had to add an oscillator to a 400S main board fitted with a 400 video board.[6] |
| Clock loses time or settings | The AA cells on the video board, then the clock circuit | Daewoo: a wrong time or date means the cells are exhausted.[7] On RBSC's board the clock still lost data with fresh cells until a 74LS157 was replaced.[6] Check for leakage from the cells at the same time. |
| Faults in the video board area, corroded connectors | Leaked clock cells | Leakage from the cells runs down the cables to the main board.[6] See Battery Explosion, Capacitor or Corrosion Damage. |
| SCC cartridge games misbehave | Known behaviour | The MSX Resource Center records odd behaviour with SCC games on this machine.[5] |
| Disk errors | The drive, the disk, the WD1772 | Clean the heads and check the drive mechanism; see Floppy Drive Repair. The controller is a WD1772 on the main board.[8] |
Capacitors
[edit | edit source]See the Daewoo CPC-400 Capacitor Replacement Guide and Capacitor Failure Symptoms.
Related pages
[edit | edit source]- Daewoo CPC-400
- Daewoo CPC-400 General Maintenance
- Daewoo CPC-400 Capacitor Replacement Guide
- Daewoo CPC-400 User Manual
References
[edit | edit source]- ↑ Daewoo, X-II (CPC-400/400S) user manual, printed page 12: the X-II is set to 220 V at the factory; insert a disk in drive A, then press the power switch at the bottom right of the front; start-up screen "X2 Bios version 1.00" and "128K Video memory installed"; a "Password:" prompt if a password has been set; holding two keys together while switching on skips a forgotten password. See Daewoo CPC-400 User Manual.
- ↑ Daewoo, X-II (CPC-400/400S) user manual, printed page 235, cartridge slot pins: 41 and 43 GND, 42 clock (3.579545 MHz), 45 and 47 +5 V, 48 +12 V, 49 sound input, 50 −12 V. See Daewoo CPC-400 User Manual.
- ↑ 3.0 3.1 Daewoo, X-II (CPC-400/400S) user manual, printed page 5: rear panel with power cord, 100 V/220 V selector (set to 220 V at first), auxiliary power outlets, fuse, stereo/mono switch, printer, RGB, cassette, video and audio sockets, colour/mono switch and expansion bus. See Daewoo CPC-400 User Manual.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Daewoo, X-II (CPC-400/400S) user manual, printed page 15, "when something is wrong": 1 no picture at switch-on, check the monitor's power and its contrast and brightness; 2 only noise on the screen, check the display connection, the computer's power (the power lamp) and that any cartridge is fully inserted; 3 an unclear, rolling or noisy picture, adjust the display and its horizontal and vertical hold, and check for interference, avoiding using a television or radio at the same time; 4 no sound, check the audio cable and the monitor's volume; 5 no response to keys, press the key combination given to bring back the cursor, and if keys still do nothing press RESET; avoid sharing a mains socket with heaters or other heavy loads, which can make the computer unstable. See Daewoo CPC-400 User Manual.
- ↑ 5.0 5.1 Daewoo CPC-400, MSX Resource Center wiki, 20 June 2026—link(accessed 2026-10-21) Rear switch for stereo PSG sound with channel A on the left and B and C on the right, the B and C channels sometimes lower than A; odd behaviour with SCC cartridge games; many CPC-400 and 400S machines not fully tested before sale; I/O port F7h bits 0 and 1 control mixing of the rear audio inputs.
- ↑ 6.0 6.1 6.2 6.3 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): clock cells on the video board leak and corrode the video board, the cables and the main board; on the board used, the crystal oscillator ran unstably until its capacitors were changed (the schematic lists some capacitor values incorrectly), at least two 74LS367 buffers were faulty, and the clock IC could not hold data until a 74LS157 was replaced; damaged IC sockets and connectors replaced; on the 400S the master oscillator is on the video board and on the 400 on the main board, so a 400 video board on a 400S main board leaves the machine without a master clock.
- ↑ Daewoo, X-II (CPC-400/400S) user manual, printed page 30: the clock is backed up by dry cells; wrong time or date means they are exhausted. See Daewoo CPC-400 User Manual.
- ↑ Photograph of the CPC-400 main board (File:Daewoo CPC-400 main board.jpg, uploaded to the MSX Resource Center wiki by Gdx on 28 June 2016): WD1772-PH floppy disk controller, DW64MX1, Z8400A, AY-3-8910A.