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Sanyo PHC-70FD Wavy General Maintenance

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Sanyo PHC-70FD power supply (100 V)
The 100 V supply on the PHC-70FD main board: fuse F501, the Rubycon 330 µF 160 V capacitor C502, transformer T501 and the large secondary capacitor C551

The Sanyo PHC-70FD Wavy is Sanyo's MSX2+ computer of 1988, sold in Japan as the Wavy70FD, with one 3.5-inch drive and a 100 V power supply on its main board.[1] No service manual or schematic for it has been published.[2] The points below come from Repair-Bas's conversion notes, the USB Secret Base pages on the machine and owners' reports on the MSX Resource Center. USB Secret Base's comparison finds only small differences on the board of the two-drive PHC-70FD2, and the Repair-Bas notes cover both models.[3]

Mains supply

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The PHC-70FD was made for Japanese 100 V mains and draws 18 W.[4] There are two ways to run it on 220 to 240 V mains.[5]

  • A step-down transformer with a 100 V output. This is the simplest way.
  • Conversion of the supply to 230 V. Repair-Bas changes three things: the primary capacitor C502, the fuse F501, and the mains lead and plug.[5]

Warning: the primary side of the supply carries mains voltage, and C502 can hold a charge after the plug is pulled. Unplug the machine and measure across C502 before touching anything near it.

Parts changed in the 230 V conversion
Part Original (100 V) Repair-Bas (230 V) RetroTechie's comments
C502 330 µF 160 V 47 µF 350 V; a higher voltage is allowed 400 or 450 V is better; at least 68 µF to store the same energy; he fitted 150 µF 400 V
F501 1.6 A glass fuse 1.6 A 250 V Rated for 230 V AC, at about 0.5 to 0.6 times the original current; a slow type
Mains lead Japanese plug Lead and plug for the country of use
Bridge rectifier Not changed Replace it, since its voltage rating is unknown
Small yellow capacitors Not changed Check that they are rated for 230 V AC; they are safety-critical

[5][6] In the photograph of the original supply, the small yellow capacitors are C510 and C513, and the bridge is D501. The board is printed "AC 125V 1.6A" beside F501.[7] Label a converted machine as such, because its rating label still says 100 V.

Opening the case

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  1. Unplug the machine and take out the clock batteries.
  2. Remove the top cover. The drive bracket is screwed to the top cover, and its 34-way ribbon cable goes to the main board.[8] Unplug it at the main board before lifting the cover away.
  3. Unscrew and lift off the metal shield plate over the main board.[9]
  4. The front cover carries the small board for the autofire slider and pause button.[10]

Clock batteries

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Two AA cells (SUM-3) in a compartment underneath keep the real-time clock running. Sanyo's label asks for them to be replaced about once a year.[11] In an MSX2 or later machine the batteries keep the time and a few settings, such as the screen mode at start-up; the computer works without them.[12]

  1. Open the compartment and look for leaked electrolyte on the cells, springs and contacts.
  2. Take out any alkaline cells. The MSX Resource Center advises against alkaline cells because they leak sooner or later, and recommends lithium AA cells or Eneloop rechargeables.[1]
  3. Clean corroded contacts as described in Battery Explosion, Capacitor or Corrosion Damage.
  4. For storage, leave the compartment empty.

Disk drive

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The drive is a TEAC FD-235F, or in some machines an FD-235GF. It is a direct-drive unit, so there is no belt to replace, and it takes its 5 V supply through the 34-way cable.[10][8] Clean the heads and check the drive as described in Floppy Drive Repair. If a drive does not work, see the Sanyo PHC-70FD Wavy Troubleshooting Guide for the capacitor repair and the replacement options.

Cartridge slots

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Sanyo's label beside the slots asks for the power to be switched off before a cartridge is put in or taken out.[13] The slots also give the easiest place to measure the supply rails: +5 V on pins 45 and 47, +12 V on 48 and −12 V on 50, with ground on 41 and 43.[14]

Memory upgrade

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The PHC-70FD has 64 KB of main RAM, and the board has empty places for two more DRAMs that take it to 128 KB.[9][1]

128 KB upgrade (MSX Resource Center summary and USB Secret Base)
Position Fit
IC113, IC114 Two 64K × 4-bit DRAMs, type 41464-12 (TMM41464AP, D41464C, MB81464 or similar)
C122, C123 0.1 µF ceramic bypass capacitors
J1102 Move the jumper; without this the machine still reports 64 KB

[1][9] Sockets make the change reversible. After the upgrade the start-up screen shows 128 KB.[9]

Capacitors

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The only published capacitor value is C502's, 330 µF 160 V. The others, and how to record them, are in the Sanyo PHC-70FD Wavy Capacitor Replacement Guide.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 Sanyo PHC-70FD, MSX Resource Center wiki—link(accessed 2026-10-21) Community specification page: Japanese market; drive facing the user; Ren-Sha Turbo (autofire) slider; mains plug for AC 100 V ±10 %, 50/60 Hz; batteries: lithium or Eneloop cells recommended, alkaline cells advised against because they leak; 128 KB RAM upgrade in summary: move jumper J1102, add two 0.1 µF capacitors at C122 and C123 and two 41464-12 RAMs at IC113 and IC114.
  2. ↑ Index of /pub/msx/docs/service_manuals, MSX Archive—link(accessed 2026-10-21) Directory of MSX service manuals; none for any Sanyo machine.
  3. ↑ PHC-70FD/PHC-70FD2, USB Secret Base—link(accessed 2026-10-21) In Japanese. Comparison of the WAVY70FD and WAVY70FD2: the FD2 drops the autofire controller and pause button and their connector and nearby resistors; it joins its two drives to the main board with a two-way cable, so the area round the 34-pin connector is much the same as on the 70FD; it uses a larger kanji ROM with level 2. Side, from the left: joystick ports 1 and 2, reset button, cassette interface. Rear: printer port, RGB output, RF channel switch, RF output, audio output, video output, mains lead, power switch.
  4. ↑ File:Sanyo PHC-70FD rating label.jpg, rating label photographed for the MSX Resource Center wiki by Mars2000you: PHC-70FD, AC 100 V, 50/60 Hz, 18 W.
  5. ↑ 5.0 5.1 5.2 Repair-Bas, Ombouw Sanyo Wavy PHC-70FD(2) naar 230 Volt (3-page PDF, in Dutch), https://repairbas.file-hunter.com/docs/other/Sanyo%20Wavy%20-%20230%20Volt%20ombouw.pdf, retrieved 2026-10-21. The PHC-70FD runs on 100 V AC because it was made only for the Japanese market; the simplest way to run it on 230 V is a step-down transformer; the tidier way is to convert it, replacing electrolytic C502 (330 µF 160 V) with 47 µF 350 V (a higher voltage is allowed), glass fuse F501 (1.6 A 120 V) with 1.6 A 250 V, and the mains lead and plug. Photographs of the 100 V supply before and after.
  6. ↑ Sanyo WAVY PHC-70FD2 needs repair, November 2010—link(accessed 2026-10-21) Thread about a PHC-70FD2. Reply by RetroTechie on the Repair-Bas conversion: 350 V is a bit tight for the replacement capacitor, 400 or 450 V is better, and for the same stored energy it should be at least 68 µF (he bought a 150 µF 400 V part about the size of the original); the fuse should be rated for 230 V AC but at a lower current, about 0.5 to 0.6 times the factory value, and a slow fuse; the small yellow capacitors at the lower left of the Repair-Bas photograph must be checked as suitable for 230 V AC because they are safety-critical; replace the bridge rectifier (the small black square part with + and − markings) because there is no way of knowing whether it is suitable for 230 V; as far as he knows there is only one board in the machine, the main board.
  7. ↑ File:Sanyo PHC-70FD power supply (100 V).jpg, from the Repair-Bas conversion document: fuse F501 with "AC 125V 1.6A" printed beside it; bridge D501 with + and − markings; primary capacitor C502, a Rubycon CE, 160 V, 330 µF, 85 °C; transformer T501 marked AE0130; yellow capacitors C510 and C513; the large secondary capacitor C551; the red wire to the drive at the right.
  8. ↑ 8.0 8.1 Repair-Bas, Diskdrive vervangen Sanyo Wavy PHC-70FD(2) (PDF, in Dutch), https://repairbas.file-hunter.com/docs/other/Sanyo%20Wavy%20PHC-70FD%20drive%20vervanging.pdf, retrieved 2026-10-21. Teac, Mitsumi and Y-E Data drives were used; the original drive takes its power through its 34-way connector; a red wire on the main board, near the drive cable, supplies the original drive(s) with 5 V; to fit a drive that needs a separate power plug, cut the red wire loose, extend it to a drive power plug (one plug per drive, only pin 1, 5 V, is used); the drive bracket is screwed to the cover; the 34-way ribbon cable plugs into the main board; using the same make of drive lets the bracket and eject button be moved across, while another make needs a hole cut in the case; a replacement drive has to be set up correctly for use as drive A or B.
  9. ↑ 9.0 9.1 9.2 9.3 PHC-70FD/PHC-70FD2 メインRAM増設, USB Secret Base—link(accessed 2026-10-21) In Japanese. To expand the main RAM from 64 KB to 128 KB: remove the top cover and the shield plate, and free the board from the case; fit sockets, two 64K × 4-bit DRAMs (Toshiba TMM41464AP, NEC D41464C, Fujitsu MB81464 or similar) and their 0.1 µF ceramic bypass capacitors, and set the jumper, without which the capacity does not increase; the start-up screen then shows 128 KB.
  10. ↑ 10.0 10.1 PHC-70FDシリーズのＦＤＤ交換, USB Secret Base—link(accessed 2026-10-21) In Japanese. The WAVY70FD drives are direct drive, unlike the belt-driven drives of Panasonic's A1 series, so a failure is more serious; replacing the drive's electrolytic capacitors has fixed some but not all; the drive is a TEAC FD-235F (some machines have an FD-235GF, whose 4-pin power connector is not used), powered through the 34-pin connector, so an ordinary PC drive cannot simply be swapped in; a Y-E Data YD-702B-6036B D (the final "D" matters) also takes its power through the 34-pin connector and can be used as a direct replacement; take off the front cover, remove the autofire and pause board from it, shave 2 to 3 mm off the disk slot and cut the eject button opening; plug the 34-pin cable in the right way round at both ends; the access lamp may not light, which is not a fault.
  11. ↑ File:Sanyo PHC-70FD underside.jpg, photograph uploaded to the MSX Resource Center wiki by Mars2000you: battery compartment for two SUM-3, AA, R6 1.5 V cells, with Sanyo's label asking for the two cells to be replaced after about a year and boxes for the year and month.
  12. ↑ 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.
  13. ↑ File:Sanyo PHC-70FD Wavy.jpg, photograph uploaded to the MSX Resource Center wiki by Jorito: label beside the cartridge slots reading "ご注意: カートリッジの抜き差しは、必ず、電源スイッチを切ってから行なってください" (always switch the power off before inserting or removing a cartridge).
  14. ↑ 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.


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