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Panasonic FS-A1FX General Maintenance

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Panasonic FS-A1FX main board DFUP0250ZAU1a
FS-A1FX main board DFUP0250ZAU1a out of the case during a recap. The power supply, with its large reservoir capacitors and inductor, is at the left

The Panasonic FS-A1FX is a 1988 MSX2+ computer with its mains transformer, power supply and belt-driven floppy drive inside the case. No Panasonic service manual for it has been found, but it shares its main board with the Panasonic FS-A1WX, whose circuit diagrams and a traced schematic with a full parts list are hosted here.[1] Its power supply is the same design as the Panasonic FS-A1GT's, and the drive takes the same belt as the turbo R machines, so the FS-A1GT guides are a useful companion to the procedures below.[2][3]

Mains supply

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The FS-A1FX is rated AC 100 V, 50/60 Hz, 20 W.[4] On 220 to 240 V mains, run it from a step-down transformer with a 100 V output and a rating well above 20 W. One owner destroyed the supply of an FS-A1WSX, a machine with the same supply design, by connecting a voltage converter the wrong way round.[5][3]

The transformer feeds the main board through a four-pin connector. On an FS-A1WX, which uses the same board, a forum member measured 12 V AC on pins 1 and 3 and 17 V AC on pin 4, with pin 2 as the common.[5][6] If you replace the transformer with a 230 V one, match those voltages. One owner who ran a board from a 24-0-24 V transformer found the switching transistor running too hot.[5] The transformer's primary, the mains lead and the power switch are at mains voltage whenever the machine is plugged in; unplug it before working inside, and sleeve every mains connection you make.

Opening the case

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No disassembly instructions for the FS-A1FX have been published. The front panel carries the built-in software switch, the Ren-Sha Turbo slider and the lamps on two small boards, which connect to the main board at CN201 and CN14. Look for these cables as you lift the top case, before pulling it clear.[1] Panasonic's disassembly order for the FS-A1GT, a later machine in a case of the same style, is in the Panasonic FS-A1GT General Maintenance guide and can be followed as a guide, checking each step against the machine in front of you.[3]

Backup cells

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The clock and settings are kept by two AA cells, type R6P (SUM-3), in a compartment in the base.[7] The MSX Resource Center recommends lithium cells or Eneloop rechargeables and advises against alkaline cells, which leak in time.[8] Take the cells out of a machine going into storage.

Floppy drive

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The MSX Resource Center gives the belt as rubber, 0.3 mm thick, 58 mm in diameter and 3 mm wide, sold as Panasonic FW-U1P501J, and points to Hans Otten's belt guide for the Panasonic MSX2+ and turbo R drives.[8] A forum member gives the original belt's circumference as about 180 mm (about 90 mm laid flat), the same for the FS-A1F, FS-A1FX, WX, WSX, ST and GT.[2] The procedure, including the warning never to unscrew the index sensor, is in the FS-A1GT maintenance guide.

The drive plugs into the main board through a 24-way ZIF socket; lift the socket's locking bar before pulling the flat cable out.[9] The FS-A1FX's floppy controller has unused motor-enable and drive-select outputs for a second drive, but the internal supply is not strong enough for two mechanical drives; a second drive needs its own power supply.[10]

Working on the main board

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The memory area of the board has fine tracks that tear easily. One FS-A1FX board lost most of its RAM-area tracks to a failed upgrade and had to be rewired with very thin wire.[5] niga2 found lifted tracks in the power supply area and cracked joints on the VDP of an FS-A1FX that switched itself off at random; see the Panasonic FS-A1FX Troubleshooting Guide.[11]

Capacitors

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The electrolytic capacitor values for the board are in BABAX's parts list; see the Panasonic FS-A1FX Capacitor Replacement Guide.[1]

Supply checks

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Measure the rails at a cartridge slot: +5 V on pins 45 and 47, +12 V on pin 48 and −12 V on pin 50, with pins 41 and 43 as ground.[12] If a rail is missing, see the power section of the troubleshooting guide.

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References

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  1. ↑ 1.0 1.1 1.2 BABAX, Panasonic MSX2+ FS-A1WX Schematic, revision 04a, 9 August 2014, with parts list revision 02. File:Panasonic FS-A1WX schematic and parts list (BABAX, Rev 04a).pdf. Title block: MAIN PWB No. DFUP0250ZAU1a for both the FS-A1FX and the FS-A1WX. Parts list: CN14 front panel LED indicator; CN201 front panel Ren-Sha and built-in software switch board; T1 transformer DDT5U7J02Z-W; V1 battery 1.5 V × 2.
  2. ↑ 2.0 2.1 Turbo-R Panasonic floppy drives, December 2017 to February 2021—link(accessed 2026-10-21) Josevil: the original belt is about 180 mm in circumference (about 90 mm measured flat), the same for the FS-A1F, FS-A1FX, WX, WSX, ST and GT; a belt of the wrong size gives the same symptoms as a faulty drive. Other posts: original belts melted onto the pulleys, cleaned off with isopropyl alcohol; a head-cleaning disk cured "disc offline" errors on one drive.
  3. ↑ 3.0 3.1 3.2 A fonte do MSX Turbo-R (e dos FX, WX e WSX tambem!)– Alexandre Souza, 9 July 2018—link(accessed 2026-10-21) In Portuguese. The power supplies of the Panasonic machines in the turbo R style of case (FS-A1FX, WX, WSX, ST and GT) are all the same apart from the switching transistor.
  4. ↑ Rating label of an FS-A1FX: "電源入力 AC 100V 50/60Hz 20W", Part No. T0136ZA. File:Panasonic FS-A1FX rating label.jpg, from the MSX Resource Center wiki (uploaded by Mars2000you, 19 September 2020).
  5. ↑ 5.0 5.1 5.2 5.3 FS-A1FX/WX/WSX memory area PCB repair, March 2005 onwards—link(accessed 2026-10-21) Alexandre Souza (9 and 10 March 2005): FS-A1FX board whose RAM area had lost most of its tracks to a failed 256 KB upgrade, repaired with very thin wire after cleaning the solder resist back with steel wool to see the tracks; transformer connector pins 1 and 3 pass through diodes and join, pin 4 feeds the 78L12 and, through a reversed diode, the 79L12; with a 24-0-24 V transformer the switching transistor ran too hot. DaBest's FS-A1WX transformer (22 March 2005): pin 1 12 V, pin 2 ground, pin 3 12 V, pin 4 17 V. Niles (18 January 2007): an FS-A1WSX supply destroyed by connecting a voltage converter the wrong way round.
  6. ↑ FS-A1WX circuit diagrams, figure 8, power unit (printed page 63). File:Panasonic FS-A1WX power supply circuit (figure 8).png, from File:Panasonic FS-A1WX circuit diagrams (pages 55 to 64).pdf. AC 100 V through the double-pole power switch to transformer T1; four-pin connector; pins 1 and 3 through D1 and D2 to the +5 V converter IC7 (MC34063P1Q); pin 2 ground; pin 4 through D7 and D6 to the 78L12 (IC29) and 79L12 (IC28).
  7. ↑ Photograph of the FS-A1FX's battery compartment on the MSX Resource Center wiki, File:Fsa1fxh.jpg (uploaded by Mars2000you, 19 September 2020): two AA cells; the label gives R6P (SUM-3), 2 個.
  8. ↑ 8.0 8.1 Panasonic FS-A1FX, MSX Resource Center wiki, 7 March 2026—link(accessed 2026-10-21) Community page: the built-in software (Cockpit) starts at boot and is skipped by holding DEL until a beep or with the front switch; drive belt rubber, 0.3 mm thick, 58 mm diameter, 3 mm wide, sold as Panasonic FW-U1P501J; links to Hans Otten's belt replacement guide for the Panasonic MSX2+ and turbo R drives and to guides for fitting a PC drive, adding a second drive and adding MSX-MUSIC; main RAM expandable to 256 KB internally; lithium or Eneloop backup cells recommended, alkaline advised against.
  9. ↑ Replace a MSX Turbo-R Diskdrive with a PC Drive– Erik Luppes, 9 June 2013—link(accessed 2026-10-21) For the FS-A1FX, FS-A1WX, FS-A1WSX, FS-A1ST and FS-A1GT; the drive connects through a 24-pin ZIF socket.
  10. ↑ Adding a second Drive to a FS-A1FX– Erik Luppes, 13 June 2013—link(accessed 2026-10-21) The TC8566F's MEN1 (pin 62) and DS1 (pin 68) outputs are not connected; wires soldered to them and taken to pins 16 and 10 of a second drive on the same cable; the power supply is not strong enough for two drives, so use an external supply; a virtual floppy drive can run from the internal supply.
  11. ↑ FS-A1FXの改造– niga2—link(accessed 2026-10-21) In Japanese. A machine that powered up only sometimes, or switched off by itself, was not cured by replacing all the electrolytics; lifted tracks in the power supply area, cracked joints on the VDP and other thinly soldered joints were found, and after repair and resoldering it ran reliably.
  12. ↑ MSX Cartridge slot, MSX Resource Center wiki, 6 July 2026—link(accessed 2026-10-21) Pins 41 and 43 GND, 45 and 47 +5 V, 48 +12 V, 50 −12 V.



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