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Panasonic FS-A1WSX General Maintenance

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Panasonic FS-A1WSX
FS-A1WSX from the front, with the firmware switch, reset button and Ren-Sha slider on the panel above the keyboard (photograph by Florian Schäffer, CC BY-SA 4.0)

Routine maintenance on the Panasonic FS-A1WSX. The WSX-specific information below comes from owners' repairs; for the supply and transformer, the closest documentation is the FS-A1WX's, covered in the Panasonic FS-A1WX General Maintenance guide. Fault-finding is in the Panasonic FS-A1WSX Troubleshooting Guide.

Safety and mains voltage

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The FS-A1WSX was built for Japan's AC 100 V mains.[1] The transformer is inside the case; unplug the machine before opening it.

The transformer is marked DDT5U7J02Z-W and joins the board through a four-pin connector.[2] That is the same part number as transformer T1 in BABAX's FS-A1WX parts list, so the WX connector voltages DaBest measured (12 V AC on pins 1 and 3, ground on pin 2, 17 V AC on pin 4) are the best guide to what a WSX transformer should give.[3][4] No measurement from a WSX itself has been published in the sources found.

Outside Japan the machine needs a step-down transformer or a replacement internal transformer. One owner ran an imported WSX from a 120 V to 100 V step-down adapter; sd_snatcher's view is that Panasonic MSX machines run on 110 to 127 V without one.[5]

Opening the case and changing the drive belt

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This procedure is from a 2015 belt change on an FS-A1WSX, whose drive is a belt-driven Matsushita EME-213MA.[6]

  1. Remove the seven Phillips screws from the underside and lift off the top of the case. Two connectors join the top to the main board; unplug them.
  2. Remove the four screws holding the drive's base and unplug the flat cable.
  3. Remove the four screws holding the drive. The screws on the black plate can stay.
  4. Remove the screw and the white plastic part next to the belt. Photograph the position of the sensor mounted with the small board beside it before disturbing anything: it is easy to refit in the wrong place. A caption on the MSX Resource Center's photographs of the EME213MA says the alignment sensor has to be moved during a belt change.[1]
  5. Clean every pulley. Melted rubber from the old belt sticks to them, and a new belt on dirty pulleys will not read discs. Isopropyl alcohol removes it.
  6. Fit the new belt, reassemble, and test with CALL FORMAT on a spare disc.

[6] The MSX Resource Center gives the belt as rubber, 0.3 mm thick, 58 mm in diameter and 3 mm wide, sold under the Panasonic part number FW-U1P501J.[1] The author of the 2015 repair used a hair band as a substitute, and also put adhesive tape in the guide groove under the black pulley to stop the belt slipping into the gap between the pulley and the frame.[6]

Backup cells

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The MSX Resource Center recommends lithium cells or Eneloop rechargeables for the backup supply and advises against alkaline cells, which leak sooner or later.[1] On the WX, the parts list gives two 1.5 V cells.[3]

Front-panel switches

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The front panel has the firmware switch, the reset button and the Ren-Sha auto-fire slider.[1] On a WX, a reset button that stuck down made the machine reset continuously, so check the reset button on a WSX that keeps resetting.[5]

RAM upgrades

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The MSX Resource Center says the WSX's RAM can be raised to 256 KB with a little soldering, and to 512 KB with a more complicated modification.[1] On one FS-A1FX board fitted in a WSX case, an earlier attempt had torn most of the tracks off the RAM area.[4]

References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Panasonic FS-A1WSX, MSX Resource Center wiki, 14 August 2026—link(accessed 2026-10-21) Community page: released October 1989 in Japan at ¥69,800 as the successor of the FS-A1WX; the cassette port is combined with the RGB connector (loading and saving work with a special cable, at a much lower volume than a normal tape interface); S-video output added; colour printing with the Panasonic FS-PC1 printer; 64 KB RAM in slot 3-0 and 16 KB SRAM; 128 KB VRAM; Yamaha V9958; PSG and MSX-MUSIC; Toshiba T9769 model B or C and a Mitsubishi gate array given as M50014; firmware bypassed only with the front switch, not the DEL key; RAM can be raised to 256 KB with a little soldering and to 512 KB with a more complicated modification; drive belt rubber, 0.3 mm thick, 58 mm diameter, 3 mm wide, sold as Panasonic FW-U1P501J; the gallery shows the EME213MA drive, with the caption that its alignment sensor must be moved during a belt change; connections RF, audio and composite video, RGB output and data recorder port, S-video, printer, two general-purpose ports, two cartridge slots, mains plug for AC 100 V ±10 %, 50/60 Hz; recommended backup batteries lithium or Eneloop, alkaline advised against "because they leak one day or another".
  2. ↑ Help with the FS A1WSX internal transformer, July 2004—link(accessed 2026-10-21) Niles: the WSX's internal transformer had failed; it is marked "DDT5U7J02Z-W", and its connector to the main board has four pins. NYYRIKKI: probably the same transformer as in the A1WX (round, about 11 W, he thought); he had his rewound for 220 V by a local repair shop and later used it in an A1ST, which originally has a different transformer and connector; the usual problems of the Panasonic FS series are the drive belt, the power supply and a worn keyboard membrane. Sonic_aka_T: his FS-A1GT's three-pin CN1 measured 19.2 V AC from pin 1 to each of pins 2 and 3, off load, on 120 V mains.
  3. ↑ 3.0 3.1 BABAX, Panasonic MSX2+ FS-A1WX Schematic, revision 04a, 9 August 2014, traced from a board marked DFUP0250ZAU1a (serial 8KCKB01501), with parts list "FS-A1WX パーツリスト PARTS LIST", 5 August 2014, revision 02. Parts list: IC1 CXA1145M; IC2 TC8566AF; IC3 M60014-0140FP (the drawing labels it "FX/WX gate array"); IC4 T9769A or B; IC5 YM2413; IC6 LM324; IC7 MC34063; IC10 MN1280R; IC11 to IC14, IC22 and IC23 MB81464-12; IC17 and IC18 MB834000; IC19 and IC20 MB8464-15L; IC21 and IC24 81C4256 shown in brackets as unfitted; IC28 79L12; IC29 78L12; Q11 2SA1598; D8 SB540; X1 16.00 MHz; X2 32.768 kHz; X4 21.47727 MHz; T1 transformer DDT5U7J02Z-W; V1 battery 1.5 V × 2; RY1 relay SZ-5; CN1 power in, CN6 RGB (8-pin DIN), CN7 cassette (8-pin DIN), CN13 drive. The drawing labels IC8 V9958 "MSX-VIDEO II"; the parts list gives "V9938 E-VDP-II". The list notes that ROMs and transistors can differ between production lots. Community reverse-engineered drawing, not a Panasonic document. Hosted as File:Panasonic FS-A1WX schematic and parts list (BABAX, Rev 04a).pdf.
  4. ↑ 4.0 4.1 FS-A1FX/WX/WSX memory area PCB repair, March 2005—link(accessed 2026-10-21) Alexandre_Taito (Alexandre Souza): an FS-A1FX board in a WSX case had most of the tracks in the user RAM area torn away by an attempted 64 KB to 256 KB upgrade, and he rebuilt them with fine wire; on the four-pin transformer connector, pins 1 and 3 pass through diodes and join, and pin 4 feeds two diodes, one to a 78L12 and one, reversed, to a 79L12; running on a 24-0-24 V transformer, the internal supply and especially the main switching transistor got too hot. 22 March 2005, quoting DaBest's measurement of a WX: pin 1 12 V, pin 2 ground, pin 3 12 V, pin 4 17 V.
  5. ↑ 5.0 5.1 FS-A1WSX powering off/resetting until I tap the machine, December 2023 to January 2024—link(accessed 2026-10-21) pawlicker: an imported FS-A1WSX, run from a 120 V to 100 V step-down adapter, switched itself off and on until the top of the case was tapped; reflowing the power switch did not help. sd_snatcher: not a common fault on these machines; suspect broken solder joints or bad capacitors in the supply, the internal connector to the transformer, or the power switch; Panasonic, Sony and Sanyo MSX machines run on about 127 V 60 Hz without a step-down transformer, unlike Toshiba ones. NYYRIKKI: if the power LED reacts to tapping, it is the supply; measure the voltages. maxis: a typical sign of a dry joint; inspect every joint with magnification. Pencioner: oxidised contacts inside the switch itself can cause it and make the switch hot. Wierzbowsky: inspect the board from both sides, starting with the AC power connector and the AC-DC section. MSXcri: his FS-A1WX's reset button sometimes stuck down, making the machine reset continuously until the button was freed.
  6. ↑ 6.0 6.1 6.2 Panasonic「FS-A1WSX」ゴムベルト交換, 29 November 2015—link(accessed 2026-10-21) The FS-A1WSX's drive is a belt-driven Matsushita EME-213MA. Procedure: remove seven Phillips screws from the underside and lift off the top, unplugging two connectors; remove the four screws holding the drive base and unplug the flat cable; remove the drive's four screws (the screws on the black plate can stay); remove the screw and the white plastic part, and photograph the position of the sensor mounted with the board beside it first, because it is easy to refit wrongly; change the belt; reassemble and test with CALL FORMAT. Melted rubber was stuck to every pulley; left in place, it stops a new belt reading discs; isopropyl alcohol removes it cleanly. The author used a Daiso "D-009" hair band (small size) as a substitute belt, and laid clear tape in the guide groove under the black pulley to stop the belt slipping into the gap between the pulley and the metal frame.



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