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Sanyo PHC-70FD Wavy Troubleshooting Guide

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Sanyo PHC-70FD main board
The PHC-70FD main board with the shield plate removed; the supply is at the top left

The Sanyo PHC-70FD Wavy (Wavy70FD) is Sanyo's single-drive MSX2+ computer of 1988.[1] No service manual or schematic has been published, and the checks below come from Repair-Bas, USB Secret Base and owners' reports.[2] Opening the case and the supply rails are covered in the Sanyo PHC-70FD Wavy General Maintenance guide.

Quick reference
Symptom First check
Dead, no power lamp Mains voltage, then fuse F501
Drive does not read, or the motor does not turn The electrolytic capacitor on the drive
SCC or other sound cartridges quiet or silent The audio mixer; see the sound fix below
Clock loses time, start-up settings lost The two AA cells underneath
CALL RUN not recognised Type CALL BC first
Still 64 KB after a RAM upgrade Jumper J1102

Dead, no power lamp

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Warning: the primary side of the supply carries mains voltage, and C502 can hold a charge after the plug is pulled.

  1. Find out what mains voltage the machine is set up for. As made, it runs on 100 V.[3] A machine converted to 230 V by the Repair-Bas method has a 47 µF or larger, 350 V or higher capacitor at C502 in place of the original 330 µF 160 V part, and a 250 V fuse at F501.[4] An unconverted machine needs a step-down transformer with a 100 V output.
  2. Unplug it, open the case and check fuse F501 beside the mains input. Repair-Bas gives the original as 1.6 A at 120 V; the board is printed "AC 125V 1.6A" beside it.[4][5]
  3. If the fuse has blown, look for the cause before fitting a new one. Check the bridge D501 for a short, and C502 and C551 for bulging tops or leaked electrolyte. If the machine has been run from the wrong mains voltage, check the whole primary side.
  4. Look at the supply area as a whole. In one PHC-70FD2 reported on the MSX Resource Center, every power supply part had been removed from the main board before the owner bought it.[6] The Repair-Bas photographs show what should be there.
  5. With the fuse good, switch on with no cartridge or drive disk fitted and measure the rails at a cartridge slot: +5 V on pins 45 and 47, +12 V on 48 and −12 V on 50, against pin 41 or 43.[7]
  6. If a rail is missing or low, replace the supply's electrolytics as set out in the Sanyo PHC-70FD Wavy Capacitor Replacement Guide before looking further.

Drive faults

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The drive is a TEAC FD-235F, or an FD-235GF in some machines. It is direct drive, so there is no belt to replace, and it takes 5 V through the 34-way cable from a red wire on the main board.[8][9]

  1. Clean the heads and check the disk as described in Floppy Drive Repair.
  2. If the motor does not turn or the drive does not read at all, replace the electrolytic capacitor on the drive's own board. One owner fixed every dead drive he had from a Wavy55FD2, 70FD and 70FD2 this way; he described it as "10V 4.7 mF", and another owner found a 4.7 µF 25 V part on his drive.[10] Read the value from your own drive and fit a part of the same capacitance and at least the same voltage.
  3. If that does not help, replace the drive. The options are:
    • another TEAC FD-235F or FD-235GF, which plugs straight in;[8]
    • a Y-E Data YD-702B-6036B D, which also takes its power through the 34-way cable; the front cover needs 2 to 3 mm shaved off the disk slot and the eject button opening cut, and its access lamp may not light;[8]
    • a drive with a separate power connector, such as a PC drive set up as drive A. Cut the red 5 V wire loose on the main board near the drive cable and extend it to a drive power plug, using only pin 1. Moving the original bracket, dust flap and eject button across is easiest with a drive of the same make; another make needs a hole cut in the case.[9]

Sound cartridges quiet or silent

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The PHC-70FD's audio mixer mutes the SCC and some other sound cartridges, because of wrong impedance matching. Sanyo's own service fix cured this for some machines with the real SCC cartridge but left other cartridges muted.[11] The community fix below changes the mixer and filter parts.

PHC-70FD and PHC-70FD2 sound fix (FRS)
Part Change
R229, R230 47 kΩ metal film
R227 27 kΩ metal film
R125 33 kΩ metal film
R115 200 kΩ metal film
R120 47 kΩ metal film
C177, C178 1.8 nF polypropylene or polystyrene
R228 Remove
C183 Replace with a wire link (0 Ω)
C181 360 pF polypropylene, polystyrene or C0G ceramic
R221 Add 18 pF 50 V polystyrene or C0G ceramic in parallel
IC117 Under the board, cut the U-shaped track joining pins 1 and 2; fit a 10 kΩ 1/8 W resistor from pin 2 to the negative pin of C184, and a 2.2 kΩ 1/8 W resistor from pin 2 to the positive pin of C115

[11]

Clock loses time

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Two AA (SUM-3) cells in a compartment underneath run the real-time clock, and Sanyo's label asks for them to be replaced about once a year.[12] Fit new cells and clean the contacts if they are corroded. The MSX Resource Center recommends lithium AA cells or Eneloop rechargeables, not alkaline cells, which leak in time.[1] The machine works without batteries, but it forgets the time and start-up settings such as the screen mode.[13]

BASIC compiler commands not recognised

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The built-in BASIC compiler is switched off at start-up. Type CALL BC first; CALL RUN and CALL TURBO ON/OFF then work.[1][14]

RAM upgrade not recognised

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After the 128 KB upgrade (two DRAMs at IC113 and IC114), the start-up screen should show 128 KB. If it still shows 64 KB, check jumper J1102; without the jumper change the extra memory is not used.[1][15] Also check that both chips are seated, the right way round, and of the 64K × 4-bit type.

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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, released 4 November 1988; mains plug for AC 100 V ±10 %, 50/60 Hz; the BASIC compiler (X-BASIC / MSX-BASIC KUN 2.0) is built in, and CALL BC must be typed before CALL RUN and CALL TURBO ON/OFF can be used; batteries: lithium or Eneloop recommended, alkaline advised against because they leak; 128 KB RAM upgrade: move jumper J1102, add 0.1 µF capacitors at C122 and C123 and two 41464-12 RAMs at IC113 and IC114; hardware sound fix for the PHC-70FD and PHC-70FD2 by sd_snatcher.
  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. ↑ 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.
  4. ↑ 4.0 4.1 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 conversion replaces 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.
  5. ↑ 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; a seven-pin module beside C502; the large secondary capacitor C551.
  6. ↑ Sanyo WAVY PHC-70FD2 needs repair, November 2010—link(accessed 2026-10-21) The owner of a PHC-70FD2 bought without its 100 V supply parts says the power components are no longer on the main board, leaving a large empty area; RetroTechie notes there is only a single board in the machine and asks which parts are missing, pointing to the Repair-Bas photographs. RetroTechie's advice on the 230 V conversion: a C502 replacement of 400 or 450 V and at least 68 µF, a 230 V fuse at 0.5 to 0.6 times the original current, check the small yellow capacitors and replace the bridge rectifier.
  7. ↑ 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.
  8. ↑ 8.0 8.1 8.2 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; otherwise the drive has to be replaced; 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 does not simply plug in; a Y-E Data YD-702B-6036B D (the final "D" matters), reportedly the drive used in the FM Towns, also takes its power through the 34-pin connector and can be fitted as a direct replacement; the front cover has to be cut: 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; the access lamp may not light, which is not a fault.
  9. ↑ 9.0 9.1 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 in these machines; 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 and extend it to a drive power plug, using only pin 1 (5 V); move the original bracket with its dust flap and the eject button to the new drive; using the same make of drive lets these 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.
  10. ↑ Fix for broken Sany Wavy 70 FD / FD2 drives, June 2013 to April 2017—link(accessed 2026-10-21) msxholder: replacing the "10V 4.7 mF" capacitor fixed all his non-working drives, which came from a Wavy55FD2, 70FD and 70FD2, and the capacitor is on the drive; another member found a 4.7 µF 25 V part on his drive; a third notes that the drives carry power and data in the same cable, so a standard PC drive needs an adapter.
  11. ↑ 11.0 11.1 MSX hardware fixes and enhancements, FRS' MSX Page—link(accessed 2026-10-21) Section 2.1, Sanyo PHC-70FD and PHC-70FD2: the fix cures SCC and other external sound cartridges being muted by wrong impedance matching (some machines had a Sanyo customer service fix, which still left many other cartridges muted), sets the mixer levels to those of Panasonic and Sony MSX2+ machines, boosts the OPLL bass, calibrates the OPLL low-pass filter like the Yamaha SFG-05 and improves the signal-to-noise ratio. Credited to Fábio Belavenuto, who traced and drew the audio circuit, and Sturaro.
  12. ↑ 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.
  13. ↑ 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.
  14. ↑ PHC-70FD/PHC-70FD2, USB Secret Base—link(accessed 2026-10-21) In Japanese. To use the BASIC compiler (MSX Bēshikkun), type CALL BC; without it the compiler is not enabled and its extended commands such as CALL RUN cannot be used.
  15. ↑ PHC-70FD/PHC-70FD2 メインRAM増設, USB Secret Base—link(accessed 2026-10-21) In Japanese. Main RAM expansion from 64 KB to 128 KB with two 64K × 4-bit DRAMs and 0.1 µF bypass capacitors; if the jumper is not set, the capacity does not increase; when the upgrade works, the start-up screen shows 128 KB.


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