Daewoo CPC-300 Troubleshooting Guide
Daewoo's own circuit diagrams for the Daewoo CPC-300 survive and are hosted as Daewoo CPC-300 Schematics. The checks below follow them, with the MSX Resource Center's notes on the machine, and use the designators printed on the diagrams. For opening the case and the mains warning, see the Daewoo CPC-300 General Maintenance guide.
Not faults
[edit | edit source]- The machine starts in the MSX-TUTOR help program. Press SELECT to reach MSX-BASIC, or enter SET SYSTEM 1 to skip the tutor at the next start (SET SYSTEM 0 restores it).[1]
- Some software crashes because the main RAM is in slot 0-2, and the usual POKE -1 workaround for subslot problems freezes the CPC-300.[1] Try the software on another MSX2 before suspecting the hardware.
- A black-and-white picture can come from the colour or monochrome switch on the rear panel.[2]
Start with the rails
[edit | edit source]Measure at the logic board test points, or at the cartridge slot:[3]
| Rail | Test point | Slot pin | Made by |
|---|---|---|---|
| +5 V | TP1 | 45, 47 | L4960 switching regulator (IC1) |
| +12 V | TP2 | 48 | KIA78012AP (IC2) |
| −12 V | TP3 | 50 | 7912 (IC3) |
| Ground | TP4 | 41, 43 |
Symptoms
[edit | edit source]| Symptom | Check first | Notes |
|---|---|---|
| Completely dead | Mains lead, power switch, the 0.5 A fuse in the filter assembly, the voltage selector | If the fuse has blown, check the bridge rectifier D1, diodes D3 to D6 and the reservoir capacitors C1, C2, C15 and C16 for a short before fitting a new one.[4] |
| +12 V and −12 V present, +5 V missing or low | The +5 V switching regulator | Check the 11.5 V winding and bridge D1, the reservoirs C1 and C2, the L4960 (IC1), its catch diode D2 (BY398), the choke L2 and the output filter L3.[4] |
| +5 V present, +12 V or −12 V missing | The linear regulators | +12 V: D5 and D6, C15 and IC2 (KIA78012AP). −12 V: D3 and D4, C16 and IC3 (7912).[4] |
| Rails correct at CN1 of the supply, missing on the logic board | The cable to CN15 and the chokes L1 to L3 | The logic board feeds each rail through a choke before the test points.[3] |
| Machine runs but resets or will not start | The reset circuit | Reset comes from a circuit with C20 (100 µF, 16 V) on the main board and the reset key assembly 990A201700.[5] Check the reset switch is not held closed and that C20 is not leaking. |
| Rails correct, no picture on any output | The V9938 and its video RAM, then the video board | The V9938 drives four 4464 video RAM chips and feeds RGB and sync to the video board through CN9.[6] If RGB works but composite and RF do not, the fault is on the video board.[7] |
| Composite or RF picture missing or noisy, RGB good | The video board | Check the +12 V feed and C13, the encoder supply C15, and the RGB input capacitors C3 to C5 on the video board.[7] |
| RGB picture dark or missing one colour | The RGB output stage on the logic board | Each colour goes out through a transistor and a 470 µF, 10 V coupling capacitor.[7] |
| No sound | The sound mixing and output capacitors | Sound from the PPI, the slots and the PSG is mixed through 10 µF capacitors on the main board and leaves the video board through C25 and C26.[6][7] |
| Clock loses time or settings | The 3 V clock battery under the video board | Check it for leakage as well as voltage.[1][8] |
| Joysticks dead | The joystick +5 V supply | The two ports share a +5 V feed with C21 (47 µF, 16 V) across it.[9] |
| Random crashes, keyboard or slot faults with good rails | The DW64MX1 gate array | The gate array handles the PPI, slot selection and memory mapper.[1] A replacement built from an Altera EPM7128 CPLD and a separate 8255 has been designed.[10] |
Capacitors
[edit | edit source]The supply's electrolytics are listed in the Daewoo CPC-300 Capacitor Replacement Guide. See also Capacitor Failure Symptoms.
Related pages
[edit | edit source]- Daewoo CPC-300
- Daewoo CPC-300 General Maintenance
- Daewoo CPC-300 Capacitor Replacement Guide
- Daewoo CPC-300 Schematics
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 Daewoo CPC-300, MSX Resource Center wiki, 4 June 2026—link(accessed 2026-10-21) MSX-TUTOR firmware runs at start-up and is skipped with SELECT; SET SYSTEM 1 skips it on the next boot and SET SYSTEM 0 restores it; the main RAM in slot 0-2 can make poorly written software crash, and the POKE -1,(15-PEEK(-1)\16)*17 workaround freezes this machine; RTC batteries under the composite video board.
- ↑ Photograph of the rear panel of a black CPC-300 (File:Daewoo CPC-300 rear connectors.jpg, uploaded to the MSX Resource Center wiki by Gdx on 16 December 2015): MONITOR COLOR/MONO switch, CH 3/4 switch, EXPANSION BUS, PRINTER, RGB, VIDEO, SOUND, RF.
- ↑ 3.0 3.1 Daewoo, CPC-300 (domestic) schematics, sheet 2 "Logic power": CN15 supply input, test points TP1 +5 V, TP2 +12 V, TP3 −12 V, TP4 ground, chokes L1 and L2 (39 µH) and L3 (100 µH), C16 to C18 (22 µF, 25 V). Sheet 8: cartridge slot pins 41 and 43 GND, 45 and 47 +5 V, 48 +12 V, 50 −12 V. Hosted as File:Daewoo CPC-300 Schematics.pdf; see Daewoo CPC-300 Schematics.
- ↑ 4.0 4.1 4.2 4.3 Daewoo, CPC-300 (domestic) schematics, sheet 1: fuse "250T 0.5A" in the filter assembly; voltage select switch 220 V/100 V; transformer secondaries 11.5 V (to the RB-401 bridge D1 and the +5 V regulator) and 16 V (to 1N4002 diodes D3 to D6 for ±12 V); IC1 L4960 with VR1 (471), L2 (150 µH), D2 (BY398) and output filter L3; C1 and C2 (2200 µF, 35 V) after the bridge; IC2 KIA78012AP with C15 (1000 µF, 35 V) at its input and C19 (100 µF, 16 V) at its output; IC3 7912 with C16 (470 µF, 35 V) at its input and C20 (100 µF, 16 V) at its output; output connector CN1: red +5 V, yellow +12 V, green −12 V, black ground. See Daewoo CPC-300 Schematics.
- ↑ Daewoo, CPC-300 (domestic) schematics, sheet 3 "CPU interface": Z-80A (IC7); main RAM of four 4464 chips; BIOS, Korean and extended BIOS ROMs IC4, IC5 and IC6; reset circuit with C20 (100 µF, 16 V), Q5 and an LS367A, with the reset key assembly 990A201700 carrying the reset switch and power LED. See Daewoo CPC-300 Schematics.
- ↑ 6.0 6.1 Daewoo, CPC-300 (domestic) schematics, sheet 6: V9938 (IC3) with four 4464 video RAM chips (IC11 to IC14), NE555 (IC38) with C15 (10 µF, 16 V), sound mixing through C12, C13 and C14 (10 µF, 16 V), light pen connector CN6, video board connector CN9 (+12 V, video reset, sound, CPU clock, composite sync, RGB). See Daewoo CPC-300 Schematics.
- ↑ 7.0 7.1 7.2 7.3 Daewoo, CPC-300 (domestic) schematics, sheet 7 "Video": video assembly 990A201400 with an MC1377P (IC1) encoder fed with RGB and sync; C13 (100 µF, 16 V) on its +12 V input and C15 (100 µF, 16 V) on the encoder supply; RGB inputs through C3, C4 and C5 (22 µF, 16 V); sound output through C25 and C26 (10 µF, 16 V); colour or monochrome switch SW2; channel switch SW1; on the logic board, RGB output transistors Q1 to Q3 with 470 µF 10 V coupling capacitors and C11 (100 µF, 16 V) on +5 V. See Daewoo CPC-300 Schematics.
- ↑ Daewoo, CPC-300 (domestic) schematics, sheet 8 "RTC, slot interface": RP5C01 (IC15) with a 3 V backup battery. See Daewoo CPC-300 Schematics.
- ↑ Daewoo, CPC-300 (domestic) schematics, sheet 5 "PSG, printer": 8910A PSG (IC16), joystick ports CN7 and CN8 with C21 (47 µF, 16 V) on their supply, printer port CN2 through an LS374. See Daewoo CPC-300 Schematics.
- ↑ DAEWOO CPC-300E MSX2 IQ 2000, SBLive.narod.ru—link(accessed 2026-10-21) In Russian. DW64MX1 replacement board built from an Altera EPM7128SLC84-15 and an i8255; pin assignment of the DW64MX1.
