Panasonic JR-300 Troubleshooting Guide
No fault on a National JR-300 has been reported in print, and Matsushita's service manual is not available online.[1] The machine starts in an unusual way: there is no BASIC in ROM for JR-300 mode, and a selector switch on the rear decides where the system is loaded from.[2]
Things that are not faults
[edit | edit source]- At power-on in JR-300 mode the machine does not show BASIC. The IPL ROM loads a system program from the device chosen on the rear selector switch, and JR-ZBASIC 1.0 comes on side A of the supplied tape.[2] With the switch set to cassette, press PLAY on the recorder; when loading finishes the screen shows "MATSUSHITA JR-300" and "JR-ZBASIC 1.0".[2]
- In automatic mode the machine tries the main floppy unit, the sub floppy unit, the ROM card and the cassette in that order, so a machine with no floppy unit or ROM card goes on to the cassette. In menu mode it shows a screen for choosing the start-up mode.[2]
- In JR-200 mode the machine starts JR-200 BASIC 5.0 from ROM, or JR-200 Disk BASIC from the JR-DA01 system disk in the sub floppy unit. It starts at the JR-200's speed; a POKE switches it to a mode about 1.33 times faster.[2]
- There is no composite or RF output. The only video output is digital RGB.[2]
- The TV control socket does nothing with any set but National's TH15-M300.[2]
Before you start
[edit | edit source]- Record the selector switch setting, then check it against the start-up mode you want.[3][2]
- Run the machine from 100 V. The plate reads AC 100 V, 50/60 Hz, 28 W.[3]
- Use a display with a digital RGB input, or a converter. The supplied RGB lead fits the TH15-M300 and National's TX-12M2 and TX-12H2 colour displays.[2]
Symptoms
[edit | edit source]| Symptom | Check first | Then |
|---|---|---|
| Nothing at all, no lights | Mains lead and supply | The power supply in the main unit |
| No picture | RGB lead and display; selector switch setting | The video section on the main board |
| BASIC tape will not load | Selector switch set to cassette, and the cassette speed on the switch matching the recording (600 or 2400 baud) | Recorder heads and levels; the tape itself |
| No sound | Front volume knob | Speaker and audio output |
| Clock loses the time when the machine is off | Clock backup battery | The board round the battery for leakage |
| Keys dead | Keyboard cable and plugs | The keyboard's MN1542 controller |
Loading the system from tape
[edit | edit source]JR-ZBASIC is on side A of the supplied tape twice, first at 2400 baud and then at 600 baud, and the demonstration program is on side B in the same order. The cassette speed is set on the rear selector switch.[2][3] If the 2400 baud copy will not load, set the switch to 600 baud and try the second copy. Clean and demagnetise the recorder's heads first, and make a modern recording of the tape before repeated use.
Power
[edit | edit source]The power supply is inside the main unit and runs from 100 V mains.[3] No circuit or voltages for it have been published. With the case open and the mains disconnected, look for bulging or leaking electrolytic capacitors and for heat damage; then, with care, measure the supply's outputs where they reach the main board. See the Panasonic JR-300 Capacitor Replacement Guide.
Clock battery
[edit | edit source]The clock chip has battery backup.[4] A clock that resets whenever the machine is switched off points to a flat battery. Replace it, and check the board round it for leakage; see Battery Explosion, Capacitor or Corrosion Damage.
Related pages
[edit | edit source]- Panasonic JR-300
- Panasonic JR-300 General Maintenance
- Panasonic JR-300 Capacitor Replacement Guide
- Capacitor Failure Symptoms
References
[edit | edit source]- ↑ Matsushita JR series, Wikipedia—link(accessed 2026-10-01) Section JR-300: delivered mainly to schools, with very few sold to the public.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 松下電器(ナショナル)の幻のパソコン・JR-300, 20 October 2024—link(accessed 2026-10-21) In Japanese. Notes from a JR-300 and its operating manual exhibited by the shop BEEP in Akihabara on 13 October 2024: no BASIC in ROM for JR-300 mode, JR-ZBASIC loaded from the supplied tape (side A at 2400 then 600 baud, demonstration on side B); start-up modes set by the rear DIP switch (main floppy, sub floppy, ROM card, cassette, JR-200 mode, an automatic mode trying them in that order, and a menu mode); cassette 600 or 2400 baud selected on the same switch; digital RGB the only video output; TV control socket for the TH15-M300 only; front volume knob for the speaker and audio output; battery-backed clock chip; three expansion connectors on the board for the floppy interface board and the kanji ROM card; joystick ports on the back of the keyboard; MN1542 in the keyboard.
- ↑ 3.0 3.1 3.2 3.3 3.4 Rear panel of the unit exhibited in 2024, photographed by tokieng (File:National JR-300 rear panel.jpg): rating plate "パーソナルコンピュータ 本体 MODEL JR-300 AC 100V 50/60Hz 28W 松下通信工業株式会社", serial 43100132; the mains lead marked "AC 100V" leaving at the right; the selector switch (切替スイッチ) at the lower left with a legend "SGD SW" for switches 1 to 6 and the cassette speeds 2400 and 600 baud; floppy disk openings above; screws along the top edge of the rear panel.
- ↑ 4.0 4.1 JR series スペック一覧, arch.jpn.org—link(accessed 2026-10-01) Catalogue specifications of the JR-300 from National's catalogue current at October 1983, including the battery-backed clock.
