JVC HC-90 Schematics
The Victor HC-90/HC-95 schematics are a nine-page set of Victor Company of Japan service drawings and lists, in Japanese, for the JVC HC-90 and HC-95 MSX2 computers. The circuit sheets are marked "Restored by MSXPro".[1] The MSX Resource Center wiki links the same restored schematics from its HC-90 page.[2] The two parts change pages carry document number 01129B and printed page numbers 10 and 11, and the packing page is printed page 12, so the set is part of a longer Victor document.[1]
Contents
[edit | edit source]| PDF page | Title (translated) | What it holds |
|---|---|---|
| 1 | Analog main board (EA-5020A) and analog sub boards (EA-6020A, EA-6021A) circuit diagram | V9938 video chip (IC501) and four µPD41464C-12 video RAM chips, MC1377P encoder, the RGB decoder (EA-6020A), the RGB and audio amplifiers on the analog sub board (EA-6021A), the 25-pin RGB connector CN503 and the supply connector CN502 (+5 V, ground, +12 V, −12 V). Title block: VDP PC board, HC-95, CS10490, drawn in Showa 60 (1985) with changes into 1986. Every electrolytic is marked with its value. |
| 2 | Digital main board (EA-1020A) circuit diagram 1/2 | Processors (µPD780C-1 Z80 and HD64180), mode switch, YM2149 sound chip and mixer, 8255, reset circuit, cassette, printer, joystick and keyboard interfaces, system ROMs, RAM board connectors. Marked EA-1020A for the HC-90 and HC-95 and EA-1021A for the HC-90(A) and HC-95(A). |
| 3 | Digital main board (EA-1020A) circuit diagram 2/2 | Kanji ROM, 8251 and 8253 with the RS-232C drivers, RP5C01 clock with backup battery BT001, MSX slot CN008, JVC extend slot CN010, floppy and mapper connectors, supply connector CN015 from the power supply (+5 V, ground, +12 V, SD, −12 V) with its filter capacitors. |
| 4 | Fan motor board (EA-8020A) circuit and copper pattern | The fan driver run from +12 V; also on the wiki as File:Victor HC-90 fan motor board EA-8020A schematic.png. |
| 5 and 6 | Board parts list (changes) | Before and after part numbers, with prices, for the EA-1020A digital main, EA-5020A analog main, EA-6020A, EA-6021A and EA-7020A boards. Includes the processor change from LH0080A to µPD780C-1, new issues of the system ROMs, the C5573 change from a ceramic to an electrolytic capacitor and the bipolar 4.7 µF 35 V capacitor at C6708. |
| 7 | Packing diagram and packing parts list | How the computer, keyboard, accessories and manuals go into the carton. |
| 8 | How to use the FDD test program | A read and write test of drives A and B, with the preparation of a formatted disk. The program listing it refers to is not in this set. |
| 9 | Waveforms (digital, analog) | Oscilloscope traces at test points on the digital board (TP-1 and TP-2 at 0.1 µs) and the analog board (20 µs). |
What this set does not contain
[edit | edit source]- There is no circuit diagram or parts list for the power supply. Forum owners repairing dead HC-95A supplies have noted this.[3]
- There is no diagram of the floppy controller board, the RAM boards or the memory mapper board.
- There are no board layouts for the digital and analog boards, no full parts lists, no dismantling instructions and no adjustment procedures.
- The FDD test program listing (pages 5 and 6 of Victor's document) is missing.
- It is drawn for the original and (A) boards. The HC-90(B), (V) and (T) changed the analog circuit, the power supply and the floppy controller board, so their boards may differ.[1][2]
Pages that cite this document
[edit | edit source]- JVC HC-90: boards, chips and revision changes.
- JVC HC-90 General Maintenance: board connectors, supply pinouts, fan board and backup battery.
- JVC HC-90 Troubleshooting Guide: supply rails, test points, chip positions and the floppy drive test.
- JVC HC-90 Capacitor Replacement Guide: the electrolytic values for every board drawn.
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 File:Victor HC-90 HC-95 schematics and parts changes.pdf, from the Internet Archive item victorhc9095schematic, "Victor HC-90/95 Schematic (JP)", whose description says it seems to cover the original HC-90 and HC-95 and the (A) revisions.
- ↑ 2.0 2.1 Victor HC-90, MSX Resource Center wiki, 7 March 2026—link(accessed 2026-10-21) Links section: "HC-90/95 Schematics", pointing at the restored schematics PDF on msxpro.com. Versions section: the HC-90(B) has an updated floppy controller board, analog circuit and power supply; the (V) and (T) follow the (B).
- ↑ Vhd interface for victor hc90/95, July 2022—link(accessed 2026-10-21) Page 8 of 31. popolon_, 2 July 2022: the schematics linked from the MSX Resource Center wiki do not contain the power supply, but they do contain the keyboard pinout.
Download: Victor HC-90 HC-95 schematics and parts changes.pdf