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Panasonic FS-A1FX Capacitor Replacement Guide

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Panasonic FS-A1FX main board DFUP0250ZAU1a
FS-A1FX main board during a recap, with the removed capacitors at the top left. The power supply's large capacitors are at the left of the board

The Panasonic FS-A1FX uses the same main board, DFUP0250ZAU1a, as the Panasonic FS-A1WX. BABAX's traced parts list for that board gives the value and rating of all 30 electrolytic capacitors, and the power supply values agree with the FS-A1WX circuit diagram.[1][2] The FS-A1FX leaves the FM sound section and the word processor parts unfitted, so some positions in the list will be empty on your board; fit capacitors only where the board has them.[3][4]

Before you start

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A recap alone may not cure an unreliable FS-A1FX. niga2 replaced every electrolytic on one that started only sometimes, with no improvement; the cause was lifted tracks in the power supply area and cracked solder joints, including on the VDP.[4] Inspect the board for both while the capacitors are out.

The transformer's primary, the mains lead and the power switch are live whenever the machine is plugged in. Unplug it before starting, and let the reservoir capacitors C34 and C57 discharge; measure across them before touching the power supply area.[2]

Power supply capacitors

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Replace these first. All are confirmed by both the FS-A1WX circuit diagram and BABAX's parts list.[2][1]

FS-A1FX power supply electrolytics
Ref Value Voltage Position in the circuit
C34 3300 µF 25 V Reservoir after rectifiers D1 and D2
C57 3300 µF 25 V Reservoir after rectifiers D1 and D2
C53 3300 µF 10 V (105 °C) Output of the +5 V converter (Vcc2 node)
C70 470 µF 6.3 V +5 V rail after L6
C35 470 µF 35 V Input of the 79L12 (−12 V)
C36 470 µF 35 V Input of the 78L12 (+12 V)
C55 1 µF 50 V Output of the 79L12

C53 is the only part in the list rated for 105 °C. It carries the switching converter's ripple current, so fit a 105 °C low-ESR capacitor there; low-ESR parts are also the usual choice for C70 after it.[1][5] A replacement with the same capacitance and a higher voltage rating can be used if it fits the space.

All electrolytics

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The full list from BABAX's parts list, grouped by value. Positions in the FM sound section are empty on the FS-A1FX.[1][3]

FS-A1WX and FS-A1FX board DFUP0250ZAU1a: electrolytic capacitors (BABAX parts list, revision 02)
Value Voltage Refs Count
3300 µF 25 V C34, C57 2
3300 µF 10 V, 105 °C C53 1
1000 µF 6.3 V C58 1
470 µF 35 V C35, C36 2
470 µF 6.3 V C2, C18, C25, C26, C27, C41, C63, C70, C71, C84, C98 11
100 µF 6.3 V C52 1
22 µF 50 V C13, C20 2
10 µF 50 V C14 1
2.2 µF 50 V C42, C43, C45, C46, C85 5
1 µF 50 V C12, C28, C55, C64 4

All are rated 85 °C except C53.[1]

Procedure

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  1. Photograph the board, then each area close up, so that the polarity of every capacitor is recorded.
  2. Work through the power supply group first, then the rest of the board. Replace one capacitor at a time, with the stripe on the same side.[6]
  3. Check each value against the printing on the part you removed. The parts list notes that some parts differ between production lots; where the part disagrees with the list, follow the part.[1]
  4. The board's tracks lift easily, especially in the power supply and memory areas. Use a temperature-controlled iron and do not lever parts out.[4][7]
  5. While the board is out, reflow any dull or cracked joints, including those on the VDP.[4]

After the recap

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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.[8] Panasonic's figure for the same supply design on the FS-A1GT is 5 V ±0.25 V.[9][10] Check the picture on composite and RGB and listen to the sound. Remaining faults are covered in the Panasonic FS-A1FX Troubleshooting Guide.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 BABAX, Panasonic MSX2+ FS-A1WX Schematic, revision 04a, 9 August 2014, with the parts list "FS-A1WX パーツリスト PARTS LIST", revision 02, 5 August 2014. File:Panasonic FS-A1WX schematic and parts list (BABAX, Rev 04a).pdf. A hand-traced community document, not a Panasonic one; the title block gives MAIN PWB No. DFUP0250ZAU1a for both the FS-A1FX and the FS-A1WX; the parts list notes that ROMs and transistors can differ between production lots. Electrolytics, all rated 85 °C except C53 (105 °C): C2 470 µF 6.3 V; C12 1 µF 50 V; C13 22 µF 50 V; C14 10 µF 50 V; C18 470 µF 6.3 V; C20 22 µF 50 V; C25, C26 and C27 470 µF 6.3 V; C28 1 µF 50 V; C34 3300 µF 25 V; C35 and C36 470 µF 35 V; C41 470 µF 6.3 V; C42, C43, C45 and C46 2.2 µF 50 V; C52 100 µF 6.3 V; C53 3300 µF 10 V; C55 1 µF 50 V; C57 3300 µF 25 V; C58 1000 µF 6.3 V; C63 470 µF 6.3 V; C64 1 µF 50 V; C70 and C71 470 µF 6.3 V; C84 470 µF 6.3 V; C85 2.2 µF 50 V; C98 470 µF 6.3 V.
  2. ↑ 2.0 2.1 2.2 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. C57 and C34 25 V 3300 µF after the rectifiers D1 and D2; C53 10 V 3300 µF at the converter's output (the +5 V Vcc2 node); C70 6.3 V 470 µF after L6 on the +5 V rail; C36 and C35 35 V 470 µF at the inputs of the 78L12 and 79L12; C55 50 V 1 µF at the 79L12's output.
  3. ↑ 3.0 3.1 FS-A1FX & FS-A1WX– up-c, 2011 to 2013—link(accessed 2026-10-21) In Japanese. On the FS-A1FX the YM2413 FM sound chip and its surrounding parts are not fitted; the FX has one 2 Mbit ROM, where the WX has four ROMs and two 8 KB SRAMs.
  4. ↑ 4.0 4.1 4.2 4.3 FS-A1FXの改造– niga2—link(accessed 2026-10-21) In Japanese. The FX uses the same board as the WX, with the FM sound parts as empty positions and only the LM324 op-amp fitted. An FX that started only sometimes, or switched itself off, was given a complete recap, which did not cure it: the board had lifted tracks in the power supply area and cracked joints on the VDP and other thinly soldered joints, and it ran reliably once they were repaired.
  5. ↑ FS-A1Fの改造 前編– niga2—link(accessed 2026-10-21) In Japanese. On the FS-A1F's switching supply, low-ESR electrolytics are recommended.
  6. ↑ Recap recommendations, June 2018—link(accessed 2026-10-21) RetroTechie, 23 June 2018: main power supply electrolytics are worth replacing whatever their condition; audio and video ones show their condition in the output; replace one capacitor at a time.
  7. ↑ FS-A1FX/WX/WSX memory area PCB repair, March 2005 onwards—link(accessed 2026-10-21) Alexandre Souza (March 2005): an FS-A1FX board whose RAM area had lost most of its tracks to a failed upgrade, rewired with very thin wire.
  8. ↑ 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.
  9. ↑ 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. See Panasonic FS-A1GT Technical Guide.
  10. ↑ 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 apart from the switching transistor.



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