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Panasonic FS-A1WX Troubleshooting Guide

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Fault-finding on the Panasonic FS-A1WX. No Panasonic fault-finding procedure for the WX has been found. The checks below come from the circuit diagrams and BABAX's traced schematic, described on the Panasonic FS-A1WX Documentation page, and from repairs reported by owners. Dismantling and routine work are in the Panasonic FS-A1WX General Maintenance guide. The Panasonic FS-A1WSX has its own guide, which refers back to this one.

Quick reference

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Symptoms and where to start
Symptom First checks Section
Dead Transformer connector voltages, reservoir capacitors, MC34063 and Q11 No power
Switches itself off and on, or comes back when the case is tapped Solder joints in the supply, transformer connector, power switch Intermittent power
Keeps resetting Reset button stuck down Constant resets
Switching transistor runs hot Transformer voltage too high No power
Drive does not turn or will not read Belt, pulleys, sensor position Drive
Clock lost at power-off Backup cells Clock

Power supply

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Panasonic FS-A1WX power supply circuit (figure 8)
The power unit, figure 8 of the FS-A1WX circuit diagrams

The transformer's four-pin connector feeds two rectifiers: pins 1 and 3 go through D1 and D2 to the reservoir capacitors C57 and C34 (25 V, 3300 µF), which supply the +5 V converter; pin 4 goes through D7 and D6 to the ±12 V regulators. The +5 V converter is IC7 (MC34063) driving switching transistor Q11, with R96 (0.2 Ω) as the current-sense resistor, R99 (3.9 kΩ) and R101 (1 kΩ) setting the output, and C53 (10 V, 3300 µF) on the output. The power unit diagram shows no crowbar on the +5 V line.[1]

No power

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  1. Check the transformer output at the connector. DaBest measured 12 V AC on pins 1 and 3 and 17 V AC on pin 4, with pin 2 as ground.[2]
  2. Check the DC across C57 and C34, then the outputs: +5 V on C53 and C70, +12 V from IC29 (78L12), −12 V from IC28 (79L12).[1]
  3. If only +5 V is missing, suspect the converter. Alexandre Souza found the MC34063 and the switching transistor the likely causes on these Panasonic supplies, followed by an open resistor or a burnt track from the rectifiers.[3] The WX's transistor is a 2SA1598 (Q11); Souza says a 2SA1643 appears to suit all the related machines.[4][3]
  4. Too high a transformer voltage can overheat the switching transistor. Souza saw this when running a related board on a 24-0-24 V transformer.[2]

Souza's isolation procedure on the Panasonic FS-A1ST Troubleshooting Guide refers to turbo R inductor numbers (L2, L6) and the turbo R crowbar. The WX power unit numbers its inductors differently and has no crowbar, so follow figure 8 when isolating the WX converter.[1]

Intermittent power

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On an FS-A1WSX that switched off and on until the case was tapped, forum members suggested, in turn:[5]

  • broken solder joints, especially in the supply; inspect both sides of the board under magnification, starting with the AC power connector and the AC-DC section;
  • bad capacitors in the supply;
  • the internal connector to the transformer;
  • the power switch, whose internal contacts can oxidise and run hot. Reflowing the switch's solder joints did not cure that machine.

NYYRIKKI added that if the power lamp reacts to tapping, the fault is in the supply.[5]

Constant resets

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MSXcri's FS-A1WX reset itself continuously whenever its reset button stuck down, until the button was moved free.[5] The reset switch is SW202 on the switch board.[6]

Drive

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  • A drive that does not turn may have a perished belt. Belt details and the replacement procedure are in the maintenance guide.
  • Melted rubber left on the pulleys stops a new belt reading discs; clean them with isopropyl alcohol.[7]
  • If the drive still fails after a belt change, check the position of the sensor next to the belt, which is easy to refit wrongly.[7][8]
  • The floppy controller is IC2 (TC8566AF), clocked by X1 (16 MHz).[4]

Clock

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If the time is lost when the machine is switched off, check the two 1.5 V backup cells (V1).[4] Figure 8 shows the backup circuit: the 3 V battery connection with D9 and D10, the reset IC10 (MN1280R), transistors Q8 and Q9, and the clock oscillator IC9 with crystal X2 (32.8 kHz).[1]

Video and sound

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The circuit pages show the video processor and its four video RAM chips (figure 4), and the FM sound, colour encoder and AV outputs (figure 6), but give no test voltages or waveforms.[9] The encoder is IC1 (CXA1145M) and the FM chip IC5 (YM2413).[4]

References

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  1. ↑ 1.0 1.1 1.2 1.3 FS-A1WX circuit diagram, figure 8, "power unit", printed page 63: AC 100 V through the double-pole power switch to transformer T1; a four-pin connector to the board (pin 2 to ground); D1 and D2 into C57 and C34 (25 V, 3300 µF each); DC/DC converter IC7 (MC34063) with switching transistor Q11 (printed "2SA598"), current-sense resistor R96 (0.2 Ω), R97 and R98 (100 Ω), R113 (22 Ω), R114 (68 Ω), timing capacitor C59 (330 pF), catch diode D8, feedback resistors R99 (3.9 kΩ) and R101 (1 kΩ), C54 (0.1 µF) and R95 (330 Ω), inductor L5 to the +5 V (Vcc2) line with C53 (10 V, 3300 µF), then L6 to +5 V with C70 (6.3 V, 470 µF); pin 4 through D7 and D6 to C36 and C35 (35 V, 470 µF) and the 78L12 (IC29, +12 V, with C56 0.1 µF) and 79L12 (IC28, −12 V, with C55 50 V 1 µF) regulators. Lower half: the clock oscillator (IC9 TC40H004P, X2 32.8 kHz), reset IC10 (MN1280R), the 3 V battery connection through D9 and D10, and the backup switching transistors Q8 and Q9. Hosted as File:Panasonic FS-A1WX circuit diagrams (pages 55 to 64).pdf. Reproduced as File:Panasonic FS-A1WX power supply circuit (figure 8).png.
  2. ↑ 2.0 2.1 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.
  3. ↑ 3.0 3.1 A fonte do MSX Turbo-R (e dos FX, WX e WSX tambem!)– Alexandre Souza, 9 July 2018—link(accessed 2026-10-21) The supplies of the Panasonic machines in the turbo R style case (FS-A1FX, WX, WSX, ST, GT) are all the same apart from the switching transistor, with components of equal or similar value, and a 2SA1643 seems to suit all of them; when the 5 V supply fails, the MC34063 and the transistor are the likely causes; if the voltage is still wrong after replacing them, check for about 22 V at MC34063 pin 6 and at the transistor's emitter, and if it is missing look for a burnt track from the rectifier diodes. The worked example is an FS-A1GT, with turbo R part numbers.
  4. ↑ 4.0 4.1 4.2 4.3 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.
  5. ↑ 5.0 5.1 5.2 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. ↑ FS-A1WX circuit diagram, figure 7, "connectors and LED switches", printed page 62: front-panel LED board with LEDs for drive, pause, caps, kana and power; switch board with the reset switch SW202, the built-in software switch SW201, the Ren-Sha speed control and the Ren-Sha LED; keyboard connectors CN10 and CN11; joystick, printer and cassette connectors. Hosted as File:Panasonic FS-A1WX circuit diagrams (pages 55 to 64).pdf.
  7. ↑ 7.0 7.1 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.
  8. ↑ 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".
  9. ↑ FS-A1WX circuit diagrams, printed pages 55 and 58 to 64: gate array pin functions; figure 3 floppy disk controller; figure 4 video processor and video RAM (four 464-type 64K × 4 DRAMs); figure 5 gate array; figure 6 FM sound, colour encoder and AV outputs; figure 7 connectors and LED switches; figure 8 power unit; figure 9 key matrix; figure 10 IC pin layouts. Pages 56 and 57 (figures 1 and 2) are not in the scan. Hosted as File:Panasonic FS-A1WX circuit diagrams (pages 55 to 64).pdf.



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