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Panasonic FS-A1FX Troubleshooting Guide

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Panasonic FS-A1WX power supply circuit (figure 8)
Power unit of the FS-A1WX, which shares its board with the FS-A1FX: transformer T1, the MC34063 converter IC7 with Q11 for +5 V, and the 78L12 and 79L12 for ±12 V

No Panasonic fault-finding guide for the Panasonic FS-A1FX has been found. It shares its main board, DFUP0250ZAU1a, with the Panasonic FS-A1WX, so the FS-A1WX circuit diagrams and BABAX's traced schematic and parts list apply to it, and its power supply is the same design as the Panasonic FS-A1GT's.[1][2] The FS-A1GT's troubleshooting guide has Panasonic's own test figures for that design. For opening the case and the drive belt see the Panasonic FS-A1FX General Maintenance guide.

Things that are not faults

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  • The built-in menu software starts at every power-on. Switch it off with the switch on the front panel, or hold DEL during start-up until the machine beeps.[3]
  • Fire buttons that repeat on their own come from the Ren-Sha Turbo auto-fire. Turn its slider on the front panel down to off.[3][4]
  • CALL MUSIC does not work and there is no FM sound. The FS-A1FX was sold without MSX-MUSIC; the FM sound chip, its parts and its ROM are not fitted.[3][5]
  • Some menu options ask for the utility disk in drive A.[3]
  • A clock that loses the time usually means flat backup cells (two AA, R6P).[6]

Fault table

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FS-A1FX faults and where to look
Symptom Check first Notes
Nothing at all Mains (100 V), the transformer, then the +5 V converter See Dead or unreliable machine.[7]
Starts only sometimes, or switches itself off Lifted tracks in the power supply area, cracked joints on the VDP and other thinly soldered joints A full recap did not cure this on niga2's machine; repairing the tracks and resoldering did.[8]
No picture, or no colour The video encoder IC1 (CXA1145) and the VDP's joints See Picture faults.
Cartridges that need ±12 V fail, or sound is missing ±12 V: transformer pin 4, D7 and D6, C36 and C35, the 78L12 and 79L12 See ±12 V rails.
Disk does not turn, or read errors The drive belt, then the heads See Floppy drive faults.
Memory errors after an upgrade attempt Torn tracks in the RAM area See Memory area.

Dead or unreliable machine

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The +5 V supply is an MC34063 switching regulator (IC7) driving a PNP transistor, Q11. The transformer's two 12 V windings are rectified by D1 and D2 into the reservoir capacitors C57 and C34; the converter's output passes through the inductor L5 to C53, the +5 V (Vcc2) node, and then through L6 and C70 to the main +5 V rail. The feedback divider R99 and R101 is taken from the Vcc2 node, before L6.[9][1] The silkscreen designators round the supply on a photographed FS-A1FX board (R99, R101, C59, D7, Q8, Q9, IC10) match the FS-A1WX drawing.[10] Unlike the FS-A1GT, neither the FS-A1WX drawing nor BABAX's parts list shows a crowbar thyristor on the +5 V output.[9][1]

With the case open, the transformer's primary, the mains lead and the power switch are live whenever the machine is plugged in. Unplug it between measurements on the primary side.

Transformer

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The transformer connects to the board through a four-pin connector. On an FS-A1WX, 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.[11] Unplug the connector, apply mains, and measure each winding on the AC range. If no winding gives any output, the primary circuit is open; most transformers of this kind have a thermal fuse buried in the windings, which opens if the transformer overheats.[12] A replacement must match the original's voltages: an FS-A1FX board run from a 24-0-24 V transformer worked, but its switching transistor ran too hot.[11]

The +5 V converter

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  1. Unplug the machine and inspect the power supply area for lifted tracks and cracked joints, which caused random shut-downs on niga2's machine.[8]
  2. Measure +5 V at a cartridge slot, on pins 45 and 47 with pins 41 and 43 as ground.[13]
  3. If it is missing or wrong, unplug the machine and lift one end of L6. This separates the main +5 V rail from the converter, while the converter keeps its feedback, which is taken before L6. Do not lift L5: the feedback would then see no output, and Souza found that on this design the output rises to the input voltage.[9][2]
  4. Power up and measure across C53. Souza accepts up to 5.2 to 5.3 V with no load.[2]
  5. If there is no output, measure the DC across C34 and C57 and at pin 6 of IC7. If the input is missing, check D1, D2 and the tracks from them; Souza's advice is to look for a burnt-out track between the rectifiers and the converter and bridge it with wire.[2][9]
  6. If the input is present, replace Q11 and IC7 first; Souza fits a 2SA1643 in all these machines. Then check R96 (0.2 Ω), R113, R114 and the Schottky diode D8 (SB540 in BABAX's list).[2][1]
  7. If the output is present but at the wrong voltage, check R99 and R101 out of circuit (see below).
  8. Refit L6 and check that +5 V holds with the machine running. Panasonic's figure for the same design on the FS-A1GT is 5 V ±0.25 V.[14]

The two documents disagree on Q11 and on the feedback resistor R99. The FS-A1WX drawing prints Q11 as "2SA598" and R99 as 3.9 kΩ; BABAX's parts list, read from a board, gives 2SA1598 and 2.09 kΩ, with R101 at 1 kΩ in both.[9][1] The MC34063 sets its output to 1.25 V × (1 + R99 ÷ R101).[15] With R101 at 1 kΩ, 3.9 kΩ would give about 6.1 V and 2.09 kΩ about 3.9 V; neither gives 5 V. On the FS-A1GT, Panasonic uses 3.09 kΩ over 1 kΩ, which gives about 5.1 V.[14] Measure the parts on your own board before replacing either.

±12 V rails

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Pin 4 of the transformer connector feeds D7 and D6, the reservoir capacitors C36 and C35 (470 µF 35 V), and the 78L12 (IC29) and 79L12 (IC28).[9][1] Measure +12 V on slot pin 48 and −12 V on pin 50.[13] Souza notes that these rails feed mainly the audio and video circuits and rarely fail.[2]

Picture faults

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The video encoder is a Sony CXA1145 (IC1) on the main board.[1][5] It is the same chip as on the HIC-1 board of the earlier Panasonic machines, so the pin checks given for it in the FS-A1MK2 guide apply: +5 V on pins 12 and 19, ground on pins 1 and 24, the 3.58 MHz clock on pin 6, sync in on pin 10 and out on pin 11, and composite video out on pin 20. Without sync on pin 10 the CXA1145 holds all its outputs at ground.[16] On the FS-A1FX board, niga2 takes the encoder's luminance output from R37 and its chroma output from C110, which makes them convenient test points.[8] If the picture breaks up or drops out when the board is flexed, reflow the VDP's joints, which niga2 found cracked.[8]

Floppy drive faults

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The belt is the usual cause of a disk that does not turn or of "Disk offline" errors. The belt is the same size as the FS-A1F's and the turbo R machines'; a belt of the wrong size gives the same symptoms as a faulty drive.[17] Replacing the belt and cleaning the heads are covered in the maintenance guide.

A PC drive can replace the original. Erik Luppes connected a Samsung SFD-321B through an adapter board carrying the 24-way ZIF socket taken from the faulty drive; only older SFD-321B revisions, which have a high-density sensor, work this way.[18]

24-way drive socket to a PC drive (Erik Luppes)
Signal 24-way pin 34-way PC drive pin
+5 V 1 Power connector
Ready 6 34
Ground 7 Power connector
Side select 9 32
Read data 11 30
Write protect 12 28
Track 00 13 26
Write gate 14 24
Write data 16 22
Step 18 20
Direction 19 18
Motor on 20 16
Drive select 0 22 10

[18] A second mechanical drive needs its own power supply: the internal supply is not strong enough for two.[19]

Memory area

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The RAM area of the board has fine tracks that tear when chips are removed carelessly. Alexandre Souza repaired an FS-A1FX board that had lost most of its RAM-area tracks to a failed upgrade: he masked the rest of the board, cleaned the solder resist back with steel wool so that the tracks could be seen, and rewired the missing connections with very thin wire, using sockets in the empty positions as anchor points.[11]

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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 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. A hand-traced community drawing; the title block gives MAIN PWB No. DFUP0250ZAU1a for both the FS-A1FX and the FS-A1WX. Parts list: IC1 CXA1145M; IC7 MC34063P1; IC28 79L12; IC29 78L12; Q11 2SA1598; D1 and D2 GP30D; D8 SB540; R95 220 Ω; R96 0.2 Ω; R97 and R98 100 Ω; R99 2.09 kΩ; (R100) not fitted; R101 1 kΩ; R113 22 Ω; R114 68 Ω; C34 and C57 3300 µF 25 V; C35 and C36 470 µF 35 V; C53 3300 µF 10 V 105 °C; C55 1 µF 50 V; C70 470 µF 6.3 V; T1 DDT5U7J02Z-W; no thyristor is listed.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 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 supplies of the FS-A1FX, WX, WSX, ST and GT are the same design with equal or similar values, apart from the switching transistor, and the 2SA1643 suits all of them; ±12 V comes from 7812 and 7912 type regulators fed through D7 and D6 and rarely fails; +12 V feeds mainly video and audio and −12 V audio; +5 V comes from an MC34063 switching regulator; when it fails, suspect the MC34063 and the transistor first, then an open resistor or a burnt track; up to 5.2 to 5.3 V with no load is acceptable; never remove the large inductor that carries the feedback, or the output rises to the input voltage (about 22 V on the GT).
  3. ↑ 3.0 3.1 3.2 3.3 Panasonic FS-A1FX, MSX Resource Center wiki, 7 March 2026—link(accessed 2026-10-21) Community page: the firmware starts at boot and is skipped by holding DEL until a beep or with the front switch; options 3 to 5 of the menu need the utility disk in drive A; Ren-Sha Turbo gives auto-fire with its speed set by a slider; the Z80A switches between 3.58 MHz and 5.37 MHz through an I/O port; no MSX-MUSIC; drive belt rubber, 0.3 mm thick, 58 mm diameter, 3 mm wide; lithium or Eneloop backup cells recommended.
  4. ↑ File:Panasonic FS-A1FX.jpg, photograph from the MSX Resource Center wiki (uploaded by Gdx, 19 October 2022): the Ren-Sha Turbo slider on the front panel, marked from OFF to MAX, beside the built-in software switch and the reset button.
  5. ↑ 5.0 5.1 FS-A1FX & FS-A1WX– up-c, 2011 to 2013—link(accessed 2026-10-21) In Japanese. On the FS-A1FX the YM2413 and its surrounding parts are not fitted, and fitting them gives no FM sound without the ROM; the FX has one 2 Mbit ROM; the RGB encoder is a Sony A1145 (CXA1145); the floppy controller is a Toshiba TC8566AF; the CMOS gate array is an M60014-0140FP.
  6. ↑ 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; label R6P (SUM-3), 2 個.
  7. ↑ Rating label of an FS-A1FX: "電源入力 AC 100V 50/60Hz 20W". File:Panasonic FS-A1FX rating label.jpg.
  8. ↑ 8.0 8.1 8.2 8.3 FS-A1FXの改造– niga2—link(accessed 2026-10-21) In Japanese. An FS-A1FX that came with a cut mains lead and missing parts powered up only sometimes, or switched off part-way; replacing all the electrolytics did not cure it; the board had lifted tracks in the power supply area, cracked joints on the VDP and cracks in other thinly soldered joints, and after repair and resoldering it ran reliably. The CXA1145's luminance output can be taken from R37 and its chroma output from C110, with +5 V from C24 and ground from R75 and C23.
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 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. Q11 printed "2SA598"; R96 0.2 Ω; R97 and R98 100 Ω; R113 22 Ω; R114 68 Ω; C59 330 pF; D8; L5 to the +5 V (Vcc2) node with C53 (10 V 3300 µF); R99 (printed 3.9 kΩ) from that node to IC7 pin 5 with R101 (1 kΩ) to ground; R95 (330 Ω) and C54 (0.1 µF); L6 and C70 (6.3 V 470 µF) to +5 V; no crowbar thyristor is drawn.
  10. ↑ File:Panasonic FS-A1FX main board DFUP0250ZAU1a.jpg, photograph uploaded to the MSX Resource Center wiki by Gdx on 2 April 2016: the power supply at the left of board DFUP0250ZAU1a, with silkscreen designators R99, R101, C59, D7, IC10, Q8, Q9 and CN15 round it.
  11. ↑ 11.0 11.1 11.2 FS-A1FX/WX/WSX memory area PCB repair, March 2005 onwards—link(accessed 2026-10-21) DaBest's FS-A1WX transformer (22 March 2005): pin 1 12 V, pin 2 ground, pin 3 12 V, pin 4 17 V. Alexandre Souza (March 2005): pins 1 and 3 pass through diodes and join; pin 4 feeds the 78L12 and, through a reversed diode, the 79L12; an FS-A1FX board run from a 24-0-24 V transformer worked, but its switching transistor ran too hot; the board's RAM area had lost most of its tracks to a failed 256 KB upgrade and was rewired with very thin wire. Niles (January 2007): an FS-A1WSX supply destroyed by connecting a voltage converter the wrong way round.
  12. ↑ Turbo R GT Power Supply gone?, July 2016 to February 2020—link(accessed 2026-10-21) RetroTechie: most transformers have a thermal fuse packed inside the windings, which blows on overheating; an FS-A1GT transformer that overheated under a heavy cartridge load gave no output afterwards.
  13. ↑ 13.0 13.1 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.
  14. ↑ 14.0 14.1 Matsushita Electric Industrial Co., Technical Guide No. 107, FS-A1GT, February 1992, printed page 14: +5 V correct if the output is 5 V ±0.25 V; circuit diagram sheet 3 (printed pages 41 and 42): the feedback divider is R2 (3.09 kΩ) and R4 (1 kΩ, 1 %). See Panasonic FS-A1GT Technical Guide.
  15. ↑ MC34063A, MC33063A, NCV33063A: 1.5 A, Step-Up/Step-Down/Inverting Switching Regulators, onsemi—link(accessed 2026-10-21) Design formula: Vout = 1.25 (1 + R2/R1), with R2 from the output to pin 5 and R1 from pin 5 to ground.
  16. ↑ Panasonic FS-A1 Mk II - no video signal, May 2015 to January 2016—link(accessed 2026-10-21) CXA1145 checks (Wierzbowsky): +5 V on pins 12 and 19, ground on pins 1 and 24, the PAL/NTSC selector on pin 7, 3.58 MHz on pin 6, C-sync in on pin 10 and out on pin 11, composite out on pin 20; l_oliveira: the CXA1145's RGB clamp needs sync from the VDP and holds all its outputs at ground without it.
  17. ↑ Turbo-R Panasonic floppy drives, December 2017 to February 2021—link(accessed 2026-10-21) Original belts melted onto the pulleys; a head-cleaning disk cured "disc offline" on one drive; Josevil: the original belt is about 180 mm in circumference, the same for the FS-A1F, FS-A1FX, WX, WSX, ST and GT, and a belt of the wrong size gives the same symptoms as a broken drive; replacement belts lasted about 5 to 10 years.
  18. ↑ 18.0 18.1 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. Mapping, 24-pin ZIF to 34-pin drive: +5 V 1 to the power connector, RDY 6 to 34, GND 7 to the power connector, Side Select 9 to 32, Read Data 11 to 30, Write Protect 12 to 28, Track 00 13 to 26, Write Gate 14 to 24, Write Data 16 to 22, Step 18 to 20, Direction Select 19 to 18, Motor On 20 to 16, Drive Select 0 22 to 10; drive jumpers moved to drive select 0 and READY on pin 34; OPA jumper fitted for 720 KB; tape over the HD hole.
  19. ↑ Adding a second Drive to a FS-A1FX– Erik Luppes, 13 June 2013—link(accessed 2026-10-21) MEN1 (pin 62) and DS1 (pin 68) of the floppy controller are unconnected and can be wired to pins 16 and 10 of a second drive; 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.



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