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Casio PV-7 General Maintenance

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Casio PV-7 main board
PV-7 main board: single-sided, with many factory jumper wires

The Casio PV-7 is a small MSX1 computer that runs from an external adapter. Casio's service documentation for it has not been published. The notes below use Casio's instruction manual (Casio PV-7 Instruction Manual), the MSX Resource Center wiki, photographs of the board and repairs and modifications reported by owners.

Power

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  • The PV-7 is rated at 10 V DC, 8 W, and takes its power from the AC adaptor AD-4810 or from the KB-7 expansion box.[1]
  • The AD-4810 takes 100 V AC, 50/60 Hz, 16 VA, and gives unregulated 10 V DC at up to 800 mA, centre negative.[2] Casio's manual says to plug it into a 100 V household outlet and that the PV-7 cannot be used abroad.[3] On 230 V mains, use a step-down transformer or a replacement adapter.
  • A replacement adapter needs to give about 10 V DC with the centre negative and at least 800 mA. Check the polarity of its plug with a meter before connecting it.
  • With the KB-7 fitted, the adaptor is not needed: the KB-7 has its own supply and powers the PV-7.[4][2]
  • Switch off before connecting or disconnecting anything.[5]
  • On the board, +5 V comes from a 7805 regulator on an aluminium heatsink.[6]

Measuring the supply

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Measure +5 V at the cartridge slot, between pin 45 or 47 and ground on pin 41 or 43.[7] Pins 48 and 50, the ±12 V pins on other MSX machines, are not connected on the PV-7, so they read nothing.[2][7]

The cartridge slot

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Cartridges that need ±12 V or the Sound IN pin do not work properly in the PV-7's own slot. The KB-7 expansion box connects Sound IN on its slots.[2] One owner made an FM-PAC work by fitting a small dual-output ±12 V DC-DC boost module fed from the board's 5 V, wiring its outputs to slot pins 48 and 50, and linking pin 49 (Sound IN) to the sound chip.[8]

RAM

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The PV-7 has 8 KB of RAM. Casio's own upgrades were the OR-208 (to 16 KB), the KB-7 (to 16 KB) and the KB-7 with an OR-216 (to 32 KB).[9] Owners have replaced the 8 KB µPD4168 with a 32 KB HM62256 static RAM: 16 KB works without cutting any tracks, while 32 KB needs extra wires for address and slot-select signals and a few track cuts.[10]

Television connection

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The PV-7's RF output goes through Casio's switch box SB-1, which must be set to COMPUTER. The RF channel switch is on the underside: set it to L for television channel 1 and H for channel 2. A television with a video input can take the composite output directly.[11][12]

Cassette

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The cassette socket is not a standard MSX one; a standard recorder needs the FA-32 or FA-33 interface.[2] If a tape will not load, Casio's chart checks the lead, the recorder's volume and, on a radio-cassette recorder, that its selector is set to tape.[11]

Opening the case

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No disassembly procedure has been published. The main board is single-sided, with many jumper wires on the component side; take care not to pull or nick them while the board is out.[13]

  1. Unplug the adapter or the KB-7, the television lead, the joysticks and the cassette interface, and remove any cartridge.
  2. Turn the machine over on a soft surface and photograph the underside, so each screw can go back where it came from.
  3. Remove the screws that hold the case together and lift the top half a little at a time.
  4. Photograph the keyboard connection and any wires between the halves before unplugging them.

Capacitors

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Advice on the MSX Resource Center forum is to replace the main supply's capacitors whatever their condition, to judge the audio and video capacitors by the picture and sound, and to leave the small decoupling capacitors unless there is a reason to change them.[14] What is known of the PV-7's capacitors is in the Casio PV-7 Capacitor Replacement Guide.

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References

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  1. ↑ Rating label of a red PV-7 (File:Casio PV-7 rating label.jpg), uploaded to the MSX Resource Center wiki by Mars2000you on 26 June 2021: "RATING: DC 10V, 8 W; use AC ADAPTOR AD-4810 or KB-7".
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Casio PV-7—link(accessed 2026-10-21) Power adapter input must be AC 100 V, 50/60 Hz, 16 VA; it can output up to 800 mA with an unregulated voltage of DC 10 V, centre negative; adapter reference AD-4810. The KB-7 expansion unit has its own power supply. Pins Sound IN, SW1, SW2, −12 V and +12 V of the cartridge connector are not connected. The tape connector is not standard; the FA-32 or FA-33 CMT interface package is needed.
  3. ↑ Casio, PV-7 取扱説明書, printed page 6 (PDF page 8): connect to a household AC 100 V outlet; it cannot be used abroad; do not bend the cord forcibly or put heavy things on it; do not use a damaged cord; pull out by the plug; if anything abnormal happens, switch off and unplug; unplug when not used for a long time. See Casio PV-7 Instruction Manual.
  4. ↑ Casio, PV-7 取扱説明書, printed page 10 (PDF page 12): when the expansion box is connected, the power adaptor is not needed. See Casio PV-7 Instruction Manual.
  5. ↑ Casio, PV-7 取扱説明書, printed page 9 (PDF page 11): switch the power off when connecting (つなげるときは電源スイッチOFFに!).
  6. ↑ Repairing a Casio PV-7 (page 2), 11 February 2024—link(accessed 2026-10-21) lmanes: the PV-7 works after replacing the VDP; RAM upgraded to 16 KB; −12 V and +12 V lines added; next job, to replace the 7805 with a TRACO switching regulator to get rid of the aluminium heatsink.
  7. ↑ 7.0 7.1 MSX Cartridge slot, 6 July 2026—link(accessed 2026-10-21) Pin table: 41 and 43 GND; 45 and 47 +5 V; 48 +12 V; 49 SOUNDIN; 50 −12 V. The ±12 V supplies are not connected on Casio MSX machines, among others; SOUNDIN is not connected on the Casio PV-7.
  8. ↑ MSX PV-7をFMPACが使えるように改造しました, 22 April 2019—link(accessed 2026-10-21) The PV-7 has no +12 V or −12 V on the cartridge slot, so the FM-PAC's FM output could not be used. A "12V Positive & Negative Dual Output power supply DC DC Step-up Boost Converter module" was fed from 5 V on the motherboard and its ±12 V outputs wired to slot pins 48 (+12 V) and 50 (−12 V); pin 49 (SOUNDIN) was also wired to the PSG for Konami SCC games. The extra wiring fits inside the case.
  9. ↑ Casio, PV-7 取扱説明書, printed page 10 (PDF page 12): PV-7 + 8 KB RAM (OR-208) → 16 KB; PV-7 + expansion box (KB-7) → 16 KB; PV-7 + expansion box + 16 KB RAM (OR-216) → 32 KB.
  10. ↑ MSX CASIO PV-7を改造してメインメモリーを32kバイトに増量, 23 March 2019—link(accessed 2026-10-21) The board's µPD4168 8 KB XRAM was replaced with a 32 KB HM62256 SRAM; without cutting tracks the RAM can be raised to 16 KB; 32 KB needed missing signals (address bus, slot select) wired in and some track cuts.
  11. ↑ 11.0 11.1 Casio, PV-7 取扱説明書, printed page 24 (PDF page 26), troubleshooting chart. See File:Casio PV-7 manual troubleshooting.jpg.
  12. ↑ Casio, PV-7 取扱説明書, printed pages 5 and 8 (PDF pages 7 and 10): the switch box (Casio SWITCH BOX SB-1, COMPUTER and TV positions) selects between the television and the PV-7; set the television to channel 1 or 2; the channel switch is on the underside of the PV-7, L for channel 1 and H for channel 2; an AV television does not need the switch box. See Casio PV-7 Instruction Manual.
  13. ↑ Repairing a Casio PV-7, February 2024—link(accessed 2026-10-21) lmanes, 10 February 2024: opening a PV-7 for the first time, the board is full of jumper wires. st1mpy, 11 February 2024: the PV-7 PCB is single-sided with many jumper wires.
  14. ↑ Recap recommendations, June 2018—link(accessed 2026-10-21) Reply by RetroTechie, 23 June 2018: main power supply capacitors in an MSX are worth replacing whatever their condition; audio and video capacitors show their condition in the output; bypass capacitors round the board can often be removed without the machine stopping; replace one at a time to avoid mixing up values or polarity.


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