Sanyo MPC-25FD General Maintenance
The Sanyo MPC-25FD is Sanyo's MSX2 desktop computer of 1985, with a 720 KB drive in the main unit, a separate keyboard and a 100 V power supply inside the case.[1] No service manual or user manual for it is available. The points below come from photographs of an opened machine, the MSX Resource Center and owners' reports.
Mains supply
[edit | edit source]- The MPC-25FD was made for Japanese 100 V mains.[1][2] On 220 to 240 V mains, run it from a step-down transformer with a 100 V output.
- The 100 V outlet on the back is for a monitor.[1] Anything plugged into it is fed through the computer's own mains lead, so a step-down transformer must be rated for the computer and the monitor together.
- The supply is a separate board at the left of the case, marked UF0673, with a TDK transformer marked AE0081.[3] Warning: the primary side of that board carries mains voltage, and its reservoir capacitor C005 can hold a charge after the plug is pulled. Unplug the machine and measure across C005 before touching the board.
Backup cell
[edit | edit source]A Sanyo Cadnica cell is soldered to the upper board.[4] Cadnica is Sanyo's name for its nickel-cadmium cells, and their electrolyte is potassium hydroxide.[5] The battery in an MSX2 keeps the real-time clock and a few settings, such as the screen mode at start-up; the machine runs without it.[6]
- Look at the cell and the board under it for white or blue-green crust, and at the tracks and chip legs nearby.
- If it has leaked, or will be left in a stored machine, desolder it. Clean any residue as described in Battery Explosion, Capacitor or Corrosion Damage, which covers the alkaline electrolyte of nickel-cadmium cells.
- Replace it with a cell of the same type and voltage as printed on the original, or leave the position empty; the clock will then not keep time.
Disk drive
[edit | edit source]The drive is a 3.5-inch 2DD unit, and the MPC-25FD formats only 2DD disks.[1] One owner's machine arrived with a dead Mitsumi D357 drive, which he replaced with a standard PC drive; he also said he had a pile of failed D357s.[2] General drive cleaning and repair is covered in Floppy Drive Repair.
Keyboard
[edit | edit source]The keyboard plugs into a 26-pin connector, the type 2 Sanyo/Philips pinout also used by the Philips NMS 8250, NMS 8255 and NMS 8280.[7]
| Pins | Signal |
|---|---|
| 1 to 11 | Row outputs Y10 to Y0 |
| 12 to 19 | Column inputs X7 to X0 |
| 20 | KANA or CODE lamp |
| 21 | CAPS lamp |
| 23 | +5 V |
| 24, 25, 26 | Ground |
[7] Keep the plug and socket clean, and do not pull the lead by its cable.
Cartridge slot and supply rails
[edit | edit source]The single cartridge slot is on the right-hand side.[1] Its supply pins follow the MSX standard: +5 V on pins 45 and 47, +12 V on 48 and −12 V on 50, with ground on 41 and 43.[8] Measure there before opening the case.
Video
[edit | edit source]The RGB output is the Japanese 21-pin RGB21 connector.[1] A European SCART cable does not work on it.[2] Use the composite video output, or a cable wired for RGB21.
Capacitors
[edit | edit source]The supply board carries the reservoir capacitor C005 and a set of smaller electrolytics. No values have been published. How to record and replace them is in the Sanyo MPC-25FD Capacitor Replacement Guide.
Related pages
[edit | edit source]- Sanyo MPC-25FD
- Sanyo MPC-25FD Troubleshooting Guide
- Sanyo MPC-25FD Capacitor Replacement Guide
- Battery Explosion, Capacitor or Corrosion Damage
- Recommended Tools
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Sanyo MPC-25FD, MSX Resource Center wiki—link(accessed 2026-10-21) Community specification page: released December 1985 in Japan; 64 KB RAM, 128 KB VRAM, Yamaha V9938; 720 KB 3.5-inch drive; separate keyboard; one cartridge slot on the right-hand side; RGB21, composite and RF outputs; a 100 V AC outlet for a monitor; the MPC-25 models can format only their own disk type.
- ↑ 2.0 2.1 2.2 MSX junk sale, November 2008 to June 2009—link(accessed 2026-10-21) Pages 2 and 3: an owner's MPC-25FD with a failed Mitsumi D357 drive, replaced with a standard PC drive; replies describing single-sided boards with many wire links, a switching power supply apparently taking 100 to 110 V AC, a WD2793 disk controller and a clock chip near the battery; a JIS keyboard without ghosting protection; an RGB connector that does not work with a European SCART cable.
- ↑ File:Sanyo MPC-25FD power supply board.jpg, cropped from a photograph uploaded to the MSX Resource Center wiki by Mars2000you as "Sabyo MPC-25FD mainboard". Read from it: board marked UF0673; mains input at the top; a 6 W 2.2 Ω wirewound resistor; a part on a heatsink; reservoir capacitor C005, its sleeve marked +85 °C; electrolytics C007, C008, C011 and C012; a TDK transformer marked AE0081; two opto-couplers beside C020 and IC052; on the secondary side C050, C055, C056, two further large electrolytics, a 100 µH choke and two heatsinks; test points TP002 and TP003.
- ↑ File:Sanyo MPC-25FD inside, upper board.jpg, photograph uploaded to the MSX Resource Center wiki by Mars2000you as "Sanyo MPC-25FD inside": a cylindrical Sanyo Cadnica backup cell soldered to the upper board, above a socketed EPROM.
- ↑ ニッケル・カドミウム蓄電池, Japanese Wikipedia—link(accessed 2026-10-21) In Japanese. Nickel-cadmium cells use an aqueous potassium hydroxide electrolyte; "Cadnica" is Sanyo Electric's registered trade mark for them.
- ↑ SANYO WAVY 35 - batteries, May 2022—link(accessed 2026-10-21) Reply by sdsnatcher73: the batteries in all MSX2 models are for the real-time clock, which keeps the time and some settings such as the screen and width the machine starts in; they are not needed for normal operation.
- ↑ 7.0 7.1 26-pin keyboard connector, MSX Resource Center wiki—link(accessed 2026-10-21) Sanyo/Philips connector pinout (type 2), for the Sanyo MPC-25F, MPC-25FD, MPC-25FK, MPC-25FS, MPC-27, MPC-2500FD and PHC-50FD2 and the Philips NMS 8250, NMS 8255, NMS 8260 and NMS 8280: pins 1 to 11 row outputs Y10 to Y0, 12 to 19 column inputs X7 to X0, 20 KANA or CODE lamp, 21 CAPS lamp, 23 +5 V, 24 to 26 ground.
- ↑ MSX Cartridge slot, MSX Resource Center wiki—link(accessed 2026-10-21) Standard MSX cartridge slot pinout: pins 41 and 43 GND, 45 and 47 +5 V, 48 +12 V, 50 −12 V.
