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Panasonic FS-A1GT General Maintenance

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Panasonic FS-A1GT main board power supply section (Technical Guide)
Power supply corner of the FS-A1GT main board, from Panasonic's Technical Guide: CN1 from the transformer at the top left, the reservoir C9, the converter IC1 and C10 below, and the ±12 V regulators IC2 and IC3 at the right

The Panasonic FS-A1GT is an MSX turbo R computer from December 1991 with its mains transformer, power supply and 3.5-inch floppy drive inside the case.[1][2] Panasonic's Technical Guide for the machine is hosted here as the Panasonic FS-A1GT Technical Guide, and the procedures below follow it. Page numbers in the references are the guide's printed page numbers.

Mains supply

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The FS-A1GT is rated for AC 100 V ±10 %, 50/60 Hz, and draws 22 W.[3] On 220 to 240 V mains, run it from a step-down transformer with a 100 V output and a rating well above 22 W, or replace the internal transformer.

Several owners on the MSX Resource Center forum have fitted a 230 V transformer with a 12-0-12 V secondary in place of the original. The part used was an Elma TT 516007 (12-0-12 V, 1.5 A, 36 VA) from Conrad, fixed to the case with an aluminium strip, and one owner reported it on an FS-A1GT in 2020. The new mains lead has to be threaded through the original rubber cable grommet; the forum advice is to widen the grommet by hand with a screwdriver and some soap, because drilling tore the rubber for one owner.[4] The primary connections carry mains voltage. Sleeve them with heat-shrink, as the forum posters did, and make sure the grommet grips the new lead so that a pull on the cable cannot reach the joints.[4]

Opening the case

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Panasonic's order of disassembly:[5]

  1. Unplug the mains lead and all cables, and take any cartridges out.
  2. Turn the machine over and remove the five screws (A) from the bottom.
  3. Lift the top cabinet a little and unplug CN16 and CN17, then take the top cabinet off. CN16 goes to the LED board and CN17 to the switch board.[6]
  4. For the keyboard, remove its three screws (B), lift it and slide it to the left, then pull the two flexible cables out of CN11 and CN12.
  5. For the floppy drive, remove the four screws (C) and the keyboard earth spring, pull the flat cable out of CN13 and lift the drive out.
  6. For the main board, with the keyboard and drive out, remove the two screws (D) from the bottom of the case, then two screws (E), five screws (F) and three screws (G) on the board. Unplug CN1 (from the transformer) and CN15 (from the battery holder) and lift the board out.

The LED board is held by three claws (H). The operating panel comes off once the LED board is out, by pressing claws (I) and (J). The switch board under it is held by two screws (K).[5]

Keyboard

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The keyboard is a flexible membrane pattern under the keys. To replace the pattern, remove the 18 screws from the back of the keyboard and lift the pattern out; check there is no dust on it before refitting. Keys fitted with arms (the long keys) come out after the pattern is removed: unhook the arm from the back of the switch board, then pull the keytop.[5] The hard-check floppy's keyboard test blames a pattern not pushed fully into its connector, poor contact or a broken track in the pattern before the main board.[7]

Backup cells and settings

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The 32 KB SRAM and the clock are kept alive by two AA cells. Panasonic shipped the machine without the cells fitted. After fitting them, set the date and time from BASIC with SET DATE "YY/MM/DD" and SET TIME "HH:MM:SS".[8] The MSX Resource Center recommends lithium AA cells or Eneloop rechargeables and advises against alkaline cells, which leak in time.[1] Take the cells out of a machine going into storage, and check the contacts of the battery holder (E5, a holder with its own cable to CN15) for corrosion.[2][6] For cleaning up leakage see Battery Explosion, Capacitor or Corrosion Damage.

Holding ESC while the machine starts erases the settings held in the SRAM.[1] Panasonic's backup test is to set the clock, run a short BASIC loop that prints TIME, switch off, and check the time is still correct when the machine is switched on again.[9]

Floppy drive

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The drive is listed in the parts list only as the complete assembly EME213MU.[2] It is belt-driven, and the rubber belt is the usual replacement part. The MSX Resource Center gives the replacement as a rubber belt 0.3 mm thick, 58 mm in diameter and 3 mm wide.[1] A two-page guide from a Japanese website, converted to PDF by Hans Otten, shows the belt path round the motor pulley and the drawings for taking the drive apart. Its drawing of the index sensor shows a soldering iron on the sensor's leads and the instruction never to remove the sensor's fixing screw, so unsolder the leads to free the belt path and leave the screw alone.[10] For general drive cleaning see Floppy Drive Repair.

The drive connects to CN13 through a 24-way flat cable with a 1.25 mm pitch. The MSX Resource Center gives the original as a Sumitomo AWM 2896 cable 100 mm long and AWM 20624 as an alternative.[1][6] The hard-check floppy's write-protect test checks the WP line from CN13 to the controller IC26, and blames IC26's soldering, CN13's soldering or a broken track if it fails.[7]

Supply checks

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Panasonic's figures for a working supply:[11]

FS-A1GT supply readings (Technical Guide, page 14)
Rail Where to measure Correct reading
+5 V Collector of Q1 (output of the DC/DC converter) 4.75 to 5.25 V
+12 V IC2 input (pin 1) and output (pin 3) About +21 V in; 10.8 to 13.2 V out
−12 V IC3 input and output (pin 3) About −22 V in; −10.8 to −13.2 V out

The guide gives the −12 V regulator's input as pin 1 of IC3. On the circuit diagram and on the board's silkscreen, IC3 (AN7912T) has ground on pin 1 and the input on pin 2, so measure the input on pin 2.[11][12]

The cartridge slots carry the same rails and are easier to reach with the case closed: pins 45 and 47 for +5 V, 48 for +12 V and 50 for −12 V, with pins 41 and 43 as ground. The MSX standard allows a cartridge up to 300 mA from +5 V, and 50 mA from each 12 V rail for all slots together.[13] The forum thread above began with an FS-A1GT whose transformer overheated while it powered a cartridge expander, so give expanders their own supply.[4]

Capacitors

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The parts list gives every electrolytic on the main board as a Panasonic aluminium part (ECEA series, with a larger ECOS part for C9); the surface-mount capacitors are ceramic chips. The power supply's reservoirs are the ones to check first. The full list from the parts list is in the Panasonic FS-A1GT Capacitor Replacement Guide.[6] For what failing capacitors look like, see Capacitor Failure Symptoms.

Video and audio connections

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Composite video and audio come out of the 8-pin DIN RGB socket, through the cable supplied with the machine; there are no separate composite or RF sockets.[1][14] The S-video socket gives the cleanest picture on a television. Jailbars on the RGB output and a quiet FM sound come from the design itself; both are covered in the Panasonic FS-A1GT Troubleshooting Guide.[15]

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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Panasonic FS-A1GT, MSX Resource Center wiki, 14 August 2026—link(accessed 2026-10-21) Community page: released December 1991; floppy drive belt specification (rubber, 0.3 mm thick, 58 mm diameter, 3 mm wide); original 24-pin drive flat cable Sumitomo AWM 2896 80C VW-1 (100 mm, 1.25 mm pitch) and an alternative AWM 20624 80C 60V VW-1 (100 to 200 mm, 1.25 mm pitch); holding ESC during boot erases the SRAM settings; composite video comes from the RGB connector through a supplied cable; recommended backup batteries lithium or Eneloop, alkaline cells advised against because they leak.
  2. ↑ 2.0 2.1 2.2 Matsushita Electric Industrial Co., Technical Guide No. 107, FS-A1GT, February 1992, printed page 65, mechanical and structural parts list. See Panasonic FS-A1GT Technical Guide (File:Panasonic FS-A1GT Technical Guide No. 107.pdf, PDF page 58). E1 power transformer DDT5L6J01Z, E2 floppy disk drive assembly EME213MU, E3 power switch ESB70707V, E4 AC cord DFJA20ZAKH, E5 battery terminal with cable DLJC8004A01A, K7 battery cover, K15 drive reinforcing plate, K16 drive mounting bracket.
  3. ↑ Technical Guide No. 107, cover (printed page 1), specification: AC 100 V ±10 % 50/60 Hz; DC 3 V for backup from two AA dry cells; 22 W; operating conditions 10 to 35 °C and 20 to 80 % humidity without condensation. File:Panasonic FS-A1GT Technical Guide No. 107.pdf, PDF page 1.
  4. ↑ 4.0 4.1 4.2 Turbo R GT Power Supply gone?, July 2016 to February 2020—link(accessed 2026-10-21) Four pages. An FS-A1GT left running with a heavy cartridge load died with a very hot transformer; the owner found no 12 V AC from the transformer and the machine worked again with the transformer from an FS-A1ST. Replies: the board takes about 12 V AC (14 to 15 V measured) from the transformer; most transformers have a thermal fuse buried in the windings that opens when they overheat (RetroTechie); the Conrad 516007 (Elma TT, 12-0-12 V, 1.5 A, 36 VA) works in the turbo R, confirmed on a GT by luppie and by cdosrun (23 February 2020); mounting with an 80 × 20 mm aluminium plate and rubber packing; the new cable is pulled through the original grommet, widened by hand rather than drilled.
  5. ↑ 5.0 5.1 5.2 Technical Guide No. 107, printed pages 12 and 13, 分解手順 (disassembly), with photographs marking each screw group A to K. File:Panasonic FS-A1GT Technical Guide No. 107.pdf, PDF pages 12 and 13.
  6. ↑ 6.0 6.1 6.2 6.3 Technical Guide No. 107, printed pages 59 to 62, electrical parts list. File:Panasonic FS-A1GT Technical Guide No. 107.pdf, PDF pages 53 to 56. Connectors: CN1 power (3 pins), CN2 and CN3 slots 1 and 2, CN4 printer, CN5 and CN6 MIDI IN and OUT, CN7 RGB, CN8 S-video, CN9 and CN10 joystick ports, CN11 and CN12 keyboard (16 pins), CN13 floppy drive (24 pins), CN15 battery (3 pins), CN16 LED board (9 pins), CN17 switch board (6 pins), CN18 microphone jack.
  7. ↑ 7.0 7.1 Technical Guide No. 107, printed pages 17 and 27 to 32, hard-check floppy (management number DF-4): test list, procedure and the parts to suspect for each failed test. File:Panasonic FS-A1GT Technical Guide No. 107.pdf, PDF pages 17 and 27 to 32.
  8. ↑ Technical Guide No. 107, printed page 5, in-service notes, section 3 (backup RAM): the backup RAM keeps the word processor's learning dictionary and BASIC SET settings, and the cells also run the clock; two AA dry cells; not fitted at the factory; SET DATE and SET TIME formats. File:Panasonic FS-A1GT Technical Guide No. 107.pdf, PDF page 5.
  9. ↑ Technical Guide No. 107, printed page 16, pass/fail checks, section 6 (backup circuit): with the backup cells fitted, set the time, run test program 3 (10 CLS:KEY OFF / 20 GET TIME T$ / 30 LOCATE 10,10:PRINT T$ / 40 GOTO 20), switch off, run it again and check the time is shown correctly. File:Panasonic FS-A1GT Technical Guide No. 107.pdf, PDF page 16.
  10. ↑ Hans Otten (converter), TurboR: replace the belt. Floppy disk drive, 2001, 2 pages, "original from a Japanese website". TurboR: replace the belt—link(accessed 2026-10-21) Photograph of the drive with the belt position marked; drawing naming the guide pin, holder, fixing screw, index sensor, LED board, belt and motor pulley; figure 4 shows a soldering iron on the sensor leads and the note このビスは絶対に外さない事 ("never remove this screw"); figure 6 shows where the two leads are clamped and led out.
  11. ↑ 11.0 11.1 Technical Guide No. 107, printed page 14, pass/fail checks, section 1 (power circuit): +5 V is made by a DC/DC converter and +12 V and −12 V by regulators, from the secondary of transformer T1. +5 V: correct if the output at the collector of Q1 is +5 V ±0.25 V. +12 V: correct if pin 1 of IC2 is about +21 V and pin 3 is +12 ±1.2 V. −12 V: correct if pin 1 of IC3 is about −22 V and pin 3 is −12 ±1.2 V. File:Panasonic FS-A1GT Technical Guide No. 107.pdf, PDF page 14.
  12. ↑ Technical Guide No. 107, printed pages 35, 36, 41 and 42: main board layout (component side) and circuit diagram sheet 3. File:Panasonic FS-A1GT Technical Guide No. 107.pdf, PDF pages 34 and 37. The silkscreen marks IC2's pins I, G, +12 and IC3's pins G, I, −12.
  13. ↑ MSX Cartridge slot, MSX Resource Center wiki, 6 July 2026—link(accessed 2026-10-21) Pin table: 41 and 43 GND, 45 and 47 +5 V, 48 +12 V, 50 −12 V; the +5 V supply must handle up to 300 mA per slot and the ±12 V supplies up to 50 mA for all slots.
  14. ↑ Technical Guide No. 107, printed page 3, names of parts: rear panel with S-video output, RGB/video and audio output, MIDI OUT, MIDI IN, printer port, external microphone socket and slot 2. File:Panasonic FS-A1GT Technical Guide No. 107.pdf, PDF page 3.
  15. ↑ MSX hardware fixes and enhancements– FRS (sd_snatcher)—link(accessed 2026-10-21) Section 2.2: the FS-A1ST and FS-A1GT audio circuits are badly calibrated (slot sound too loud, OPLL too quiet and over-filtered, overall output weak), with replacement values for the FS-A1GT: C17 and C18 1.8 nF, R50 22 kΩ, R47 15 kΩ, R55 47 kΩ, C51 180 pF, C45 150 pF (all 0805 SMD). Section 2.3: jumpers J1 and J2 on the FS-A1GT board select composite video (default) or composite sync for the DIN RGB socket; the composite signal causes jailbars on RGB; cut J2 and bridge J1 to send CSYNC, after which composite video is taken from the S-video socket with an S-video to composite cable.



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