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Panasonic FS-A1 Troubleshooting Guide

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Panasonic FS-A1 (red), rear view
Rear of a red FS-A1. The square power input for the FS-AA51 adapter is at the right

No Panasonic fault-finding guide for the Panasonic FS-A1 has been found. The checks below use the community schematic and parts list of the DFUP0110ZAP2 main board, hosted as the Panasonic FS-A1 Schematic, and the faults reported by owners. For the adapter, the backup cells and the start-up keys, see the Panasonic FS-A1 General Maintenance guide.

Things that are not faults

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  • The machine starts in the DESKPAC menu. Hold DEL during start-up, until it beeps, to go straight to BASIC.[1]
  • The PAUSE key stops the machine until it is pressed again.[1]
  • With a Sunrise CF/IDE interface fitted, holding DEL at start-up also disables its partitions. The MSX Resource Center suggests redefining the key with IDKEYSET.COM or using the interface's BIOS 2.50b, which uses STOP instead.[1]
  • Starting with ESC held ignores the settings stored with BASIC's SET commands.[2]

Fault table

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FS-A1 faults and where to look
Symptom Check first Notes
Nothing at all, power lamp dark The FS-AA51 adapter (DC 9 V and AC 18 V outputs), its plug, the power switch SW1 The adapter takes 100 V mains. Its 9 V output is rectified and smoothed inside the adapter.[3][4]
Power lamp lit, machine does not start +5 V at slot pin 45 or 47; C1, IC18 and Q3 The reset IC IC19 holds the machine in reset below about 4.0 to 4.3 V.[2]
Machine runs (sound, keyboard) but no picture The 18 V AC from the adapter, D2, D3, IC16, IC17 and their capacitors The hybrid board that produces the video needs ±12 V.[4]
Picture on RGB but not on composite or RF, or the reverse The hybrid board IC1 (BX7396WB) and the RF converter RF1 The hybrid board carries the video encoder; the RF converter is a separate module.[2]
Cartridges with FPGAs (Wondertang, Flashjack) crash or fail to start Slot contacts; C24 and C25 beside the slot Cutting C24 and C25 cures it, with no side effects reported.[1]
Clock loses the time, settings lost at power-on The two 1.5 V backup cells and their contacts See Battery Explosion, Capacitor or Corrosion Damage for leaked cells.[2]
Cassette loading fails A known good recording first, then the cassette interface on the hybrid board IC1 The hybrid board carries the cassette interface as well as the video encoder and audio amplifier.[2]

Power checks

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Measure with the machine running, 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.[5] If +5 V is missing:

  1. Unplug the adapter from the computer and measure its two outputs, rated 9 V DC and 18 V AC. A missing 9 V output points to the rectifier or the smoothing capacitor inside the adapter.[3][4]
  2. With the adapter plugged in and the machine on, measure across C1 (4700 µF, 16 V), the 9 V reservoir on the main board.[2]
  3. Check the regulator IC18 (M5236L) and the pass transistor Q3 (2SB941-Q). The output is set by R33 (13 kΩ) and R34 (4.3 kΩ); a drifted or open resistor there moves the +5 V rail.[2]
  4. Check C22 (330 µF, 6.3 V) on the +5 V output for leakage or a short.[2]

If ±12 V is missing, check the 18 V AC at the input, the diodes D2 and D3, the reservoirs C26 and C2 (470 µF, 35 V each), the regulators IC16 (78L12) and IC17 (79L12), and their output capacitors C17 and C27 (220 µF, 16 V each).[2]

Clock and reset

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The video crystal is X1 (21.47727 MHz) and the clock crystal X2 (32.768 kHz).[2] A machine that powers up with a blank screen and does not respond, with the rails correct, can be held in reset: measure the output of the reset IC IC19 (MN1280-R), which goes low when the supply drops below about 4.0 to 4.3 V.[2]

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References

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  1. ↑ 1.0 1.1 1.2 1.3 Panasonic FS-A1, MSX Resource Center wiki, 7 March 2026—link(accessed 2026-10-21) Community page: DESKPAC bypassed by holding DEL at start-up until a beep; with a CF/IDE Sunrise interface the DEL key clashes and has to be redefined with IDKEYSET.COM (or BIOS 2.50b, which uses STOP); the pause button pauses the system; the daughterboard is not a HIC-1 board; slot instability with FPGA cartridges such as Wondertang or Flashjack cured by cutting C24 and C25 next to the slot; lithium or Eneloop backup cells recommended.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 BABAX, Panasonic MSX2 FS-A1 board (PWB) Rev.02 schematic, PWB DFUP0110ZAP2, revision 01a, 14 April 2015, with parts list. Hosted as File:Panasonic FS-A1 schematic and parts list (BABAX, Rev 01a).pdf; see Panasonic FS-A1 Schematic. Page 1: input CN3 (DC 9 V 1.2 A, AC 18 V 170 mA) through SW1 and choke L4; C1 4700 µF 16 V on the 9 V input; +5 V from IC18 (M5236L) and pass transistor Q3 (2SB941-Q), R33 13 kΩ and R34 4.3 kΩ feedback, C22 330 µF 6.3 V; +12 V from IC16 (78L12) via D2 and C26 (470 µF 35 V), output C17 (220 µF 16 V); −12 V from IC17 (79L12) via D3 and C2 (470 µF 35 V), output C27 (220 µF 16 V); battery 2 × 1.5 V via D6 and D7; IC19 (MN1280-R) reset IC, output low below 4.0 to 4.3 V; X1 21.47727 MHz, X2 32.768 kHz; note on starting with ESC held. Parts list: IC1 hybrid IC BX7396WB (RGB to video encoder, cassette interface, audio amplifier), carrying a ROHM BA7230LS encoder, a 74LS123, and BA6993F and BA4558F op-amps; RF1 Mitsumi RF converter; C24 and C25 0.0047 µF ceramic.
  3. ↑ 3.0 3.1 Panasonic FS-AA51, MSX Resource Center wiki, 17 September 2025—link(accessed 2026-10-21) Input AC 100 V 50/60 Hz 23 VA; output DC 9 V 1.2 A and AC 18 V 170 mA; same as the Sony AC-HB3; not the same as the Sony AC-HB1 series or AC-HB2P.
  4. ↑ 4.0 4.1 4.2 初代 FS-A1の改造– niga2—link(accessed 2026-10-21) In Japanese. Inside the adapter the AC 18 V comes straight from the transformer and the DC 9 V is rectified and smoothed; inside the FS-A1 the AC 18 V is rectified and regulated to ±12 V, which feeds the slots and the hybrid IC that handles video and audio, so without it there is no picture.
  5. ↑ 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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