Mitsubishi ML-F80 Troubleshooting Guide
No service manual or circuit diagram for the Mitsubishi ML-F80 has been found, so fault-finding rests on the MSX standard and on what can be seen on the board. Work from the supply rails to the chips.[1]
Rails
[edit | edit source]Measure at a cartridge slot, with pin 41 as ground:[2]
| Rail | Point | Notes |
|---|---|---|
| +5 V | Slot pins 45 and 47 | Logic supply |
| +12 V | Slot pin 48 | Also feeds the video RAM |
| −12 V | Slot pin 50 | |
| −5 V | Pin 1 of a D416C-2 video RAM, against pin 16 | Not on the slot |
The D416C-2 is NEC's µPD416, which needs +5 V on pin 9, +12 V on pin 8 and −5 V on pin 1.[3][1] The video RAM needs all three, so measure all four rails before suspecting a chip.
If every rail is missing, check the mains lead and switch, then the supply. The power cord, switch and transformer carry mains voltage; unplug the machine before working near them.[4]
Supply shorted by a load
[edit | edit source]A rail that collapses only with something plugged in points at that device:
- Remove every cartridge and controller and measure again. Each slot may draw up to 300 mA from +5 V.[2]
- The joystick ports give +5 V on pin 5 at up to 50 mA. An Amiga mouse shorts +5 V to ground when its second button is pressed, and Atari and Commodore paddles can short it through their buttons or potentiometers. A Sega Master System pad or an FM Towns Marty pad can damage the output on pin 8.[5]
- A failed ceramic decoupling capacitor can short a rail to ground. On the MSX Resource Center forum, the advice is to feel which chip or part runs warm after a few minutes.[6]
Rails correct, machine not starting
[edit | edit source]| Check | What it shows |
|---|---|
| Press Caps Lock; the key has its own LED[7] | If it toggles, the processor and ROM are probably running and the fault is more likely in the video path[6] |
| The oscillator CXO-043B (21.3750 MHz) | The oscillator on the main board; check its output with an oscilloscope or frequency counter[1] |
| Feel the D780C-1, the video chip area and the RAM after a few minutes | A part that stays cold may have no clock or supply[6] |
| Try a RAM cartridge | An easy test of the on-board RAM[6] |
| Reseat the two KEY connectors | A loose keyboard connector can leave keys dead[1] |
Picture faults
[edit | edit source]| Symptom | Check |
|---|---|
| No RGB from a British machine | The British ML-F80 has composite and RF only; RGB is fitted to the French model.[8] Owners have added RGB with a TMS-RGB board in place of the video chip.[9] |
| No picture on RF or composite | The wires and plugs between the main board and the video and RF board 55-4007D.[1] |
| Garbled screen or wrong characters | +12 V and −5 V at the video RAMs, then the eight D416C-2 chips.[3] |
| Dull or noisy picture | The electrolytic capacitors on the video and RF board and next to the video socket; failing capacitors in the video circuits show in the picture.[10] See the Mitsubishi ML-F80 Capacitor Replacement Guide. |
Sound and ports
[edit | edit source]- No sound: the sound socket and the capacitors near it, then the AY-3-8910A.[1][10]
- Joystick dead: test with a known good MSX joystick, then the port's pins against the MSX pinout.[5]
- Printer dead: try the printer and cable on another computer, then check the solder joints of the printer connector CON-PR on the main board.[1]
Related pages
[edit | edit source]- Mitsubishi ML-F80
- Mitsubishi ML-F80 General Maintenance
- Mitsubishi ML-F80 Capacitor Replacement Guide
- Panasonic CF-2700 Troubleshooting Guide, a fully documented MSX1 of the same period
- Capacitor Failure Symptoms
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 File:Mitsubishi ML-F80 main board.jpg, photograph of an ML-F80 main board uploaded to the MSX Resource Center wiki by Mars2000you on 7 April 2020. Read from it: main board J0510425K with a separate video and RF board 55-4007D (carrying an LVA510 IC, a 74LS04 and a crystal); cartridge connectors CN1 and CN2; NEC D780C-1; HN613256P mask ROM (IC2D); eight M5K4164ANP DRAMs (IC5D to IC8E area); eight NEC D416C-2 video RAMs (IC7A to IC10B); M5L8255AP-5 PPI; GI AY-3-8910A; CXO-043B oscillator marked 21.3750 MHz; two white keyboard connectors marked KEY; a relay RL beside the joystick and cassette sockets; printer connector CON-PR; LED connector CON-LED.
- ↑ 2.0 2.1 MSX Cartridge slot, MSX Resource Center wiki, 6 July 2026—link(accessed 2026-10-21) Pinout of the standard MSX cartridge slot: 41 and 43 GND, 42 CLOCK, 44 SW1, 45 and 47 +5 V, 46 SW2, 48 +12 V, 49 SOUNDIN, 50 −12 V; the +5 V supply must handle up to 300 mA per slot and the ±12 V supplies up to 50 mA for all slots.
- ↑ 3.0 3.1 Matsushita, Service Manual: Personal Computer CF-2700 (IED84113035C2), printed page 9, Fig. 7: µPD416C video RAMs with +5 V on pin 9, +12 V on pin 8, −5 V on pin 1 and ground on pin 16. See Panasonic CF-2700 Service Manual.
- ↑ File:Mitsubishi ML-F80 rating label.jpg, rating label: 220-240 V~, 50/60 Hz, 27 W.
- ↑ 5.0 5.1 General Purpose port, MSX Resource Center wiki, 13 December 2025—link(accessed 2026-10-21) Pin 5 +5 V (50 mA), pin 8 output, pin 9 ground. Devices that can cause damage: Amiga mouse (pin 5 is button 2 on the Amiga, so pressing it shorts +5 V); Atari and Commodore paddles (a short through the second button, or through the potentiometers when both are at minimum); FM Towns Marty pad and Sega SG-1000, Mark III and Master System pads (a button on pin 8 can damage that pin when it is high); DE9 RS-232C devices.
- ↑ 6.0 6.1 6.2 6.3 Panasonic CF-2700, October and November 2025—link(accessed 2026-10-21) Advice to the owner of a dead MSX1 (a CF-2700): mcolom, a Caps Lock LED that toggles shows that the Z80 and ROM are probably working; without an oscilloscope, check whether the Z80, VDP and RAM get warm after a few minutes; a failed ceramic capacitor can short Vcc to ground. Briqunullus: an external RAM cartridge is an easy test of the RAM.
- ↑ File:Mitsubishi ML-F80.jpg and the MSX Resource Center wiki gallery for the ML-F80 (File:Ml-f80c.jpg, French model): power LED above the keyboard, a red LED in the Caps Lock key, mains lead and RGB DIN socket at the rear.
- ↑ Mitsubishi ML-F80, MSX Resource Center wiki, 7 March 2026—link(accessed 2026-10-21) French version with AZERTY keyboard and RGB DIN video output; UK version with QWERTY keyboard and PAL RF and composite video output; connections: RF output (PAL version only), mono sound, composite video (PAL version only), RGB output (French version), data recorder, Centronics-compatible printer port, two general ports, two cartridge slots.
- ↑ Mitsubishi ML-F80, September 2022—link(accessed 2026-10-21) thecaver99: the PAL ML-F80 has only composite output where the French version has RGB. sdsnatcher73: adding RGB is not easy but not impossible, see TMS-RGB. gdx: if there is no space under the RF converter for an RGB connector, replace the VDP with the TMS-RGB and find a way to fit an RGB connector.
- ↑ 10.0 10.1 Recap recommendations, June 2018—link(accessed 2026-10-21) RetroTechie, 23 June 2018: in an MSX, capacitors in the analogue audio and video circuits show their condition in the picture or sound; the main power supply capacitors are worth replacing whatever their condition.
