Sony HB-F900 Troubleshooting Guide
No service manual or schematic for the Sony HB-F900 is known to be available, so fault-finding relies on the faults owners have reported and on its standard MSX2 parts.[1][2] The Sony HB-F900 General Maintenance guide covers opening the case and the drives.
Quick symptom table
[edit | edit source]| Symptom | Cause found | Section |
|---|---|---|
| No cartridge recognised in either slot | Two failed SN74LS367 bus buffers | Cartridges |
| Red or coloured start-up screen; no BASIC | Settings corrupted by a low backup cell | Settings |
| "Disk Offline" from FILES | Drive fault, or a replacement drive without READY | Drives |
| No superimposed picture through the HBI-F900 | Not found | Superimpose |
Cartridges not recognised
[edit | edit source]On one HB-F900, no cartridge worked in either the front or the rear slot. The repairer found that the address, data and control lines to the slots all pass through buffer chips. With a cartridge fitted, he compared the inputs and outputs of the buffers with an oscilloscope: two signals were present on the inputs and missing on the outputs. Replacing a pair of SN74LS367 buffers, fitted in sockets, cured it.[3]
- Take the bottom panel off to reach the underside of the main board.[3]
- With the machine running, probe the input and output of each buffer channel on the slot lines with an oscilloscope or logic probe.
- Replace any buffer with activity on its input and none on its output.
Start-up screen and settings
[edit | edit source]An HB-F900 that started with a red screen and would not reach BASIC was cured by resetting its stored settings: press SHIFT+F1, type SET TITLE "" and SET SCREEN, then reset. The start-up colour is itself a setting, and SET TITLE "",1 gives the usual blue screen. The settings become corrupted when the Ni-Cd backup cell is low after a long time unused, and a red screen with "@ D" under the MSX logo was put down to a dying cell, which an experienced member advised removing.[4] See the backup battery section of the Sony HB-F900 General Maintenance guide.
Floppy drive faults
[edit | edit source]One owner's HB-F900 answered "Disk Offline" to the FILES command with its original drives.[4] Another owner's drives also stopped working, while cartridges still worked.[1]
- Clean the heads and check the drives turn; see Floppy Drive Repair. The drives have no belt.[3]
- If a replacement drive's LED stays lit, the cable is upside down.[4]
- A replacement PC drive needs the READY signal on pin 34. Without it, an MSX converted drive tested in a Sony HB-F700 worked but froze the machine when it booted into BASIC until a formatted disk was inserted, while games and MSX-DOS booted normally.[4] Bridge pins 33 and 34 to provide READY, as described in the Sony HB-F900 General Maintenance guide.
- The machine works with one drive, or none, and reports an error only when the missing drive is used.[4]
- If disks catch as they come out, see repairBas's eject modification in the maintenance guide.[5]
HBI-F900 superimpose fault
[edit | edit source]One owner reports an HB-F900 and HBI-F900 pair in which the HB-F900 could change the HBI-F900's settings from BASIC and its own picture reached the HBI-F900's video output, but video from the HBI-F900's input did not come through for superimposing. No cause was found and no schematic was offered.[1] Check the 50-pin Centronics cable, which is wired pin to pin, before suspecting either unit.[3]
No power
[edit | edit source]The power supply sits at the back left of the case with its transformer and a large reservoir capacitor.[6] No schematic of it has been published, so trace it from the board: check the mains lead and any fuse first, then the transformer secondaries and the regulator outputs. The HB-F900 is built for 100 V; check that it has been run from a suitable step-down transformer.[7]
Related pages
[edit | edit source]- Sony HB-F900
- Sony HB-F900 General Maintenance
- Sony HB-F900 Capacitor Replacement Guide
- Sony HB-F700 Troubleshooting Guide
- Capacitor Failure Symptoms
References
[edit | edit source]- ↑ 1.0 1.1 1.2 HB-F900 + HBI-F900 troubleshooting, May 2024—link(accessed 2026-10-21) Post by drone, 11 May 2024: an HB-F900 with an HBI-F900; cartridges work but the drives do not; the HB-F900 can change HBI-F900 settings from BASIC, but video from the HBI-F900 input does not come through for superimposing; he asks for any service documents or schematics, including Japanese ones, and none are posted.
- ↑ Sony HB-F900, MSX Resource Center wiki, 7 May 2026—link(accessed 2026-10-21) Community page: an MSX2 for the Japanese professional market that can superimpose its picture on a video signal (genlock) through a video interface connector on the back and a DSP board; used with the HBI-F900 AV Creator; black (B) or cream (W); separate KBD-13 or KBD-13(B) keyboard of HB-F500 design; supplied with a DIN-8 to RGB21 cable, MOS-1 mouse and the Wordship word processor on two disks; 1986; ¥148,000; 256 KB of RAM in slot 3-1; 128 KB VRAM; Yamaha V9938; PSG in the Yamaha S1985 MSX-Engine; two 720 KB 3.5-inch drives, internal speaker, reset button, JIS level 1 kanji ROM; Z80A from Sharp (LH0080A) or NEC (μPD780C); Western Digital WD2793A-PL floppy controller; an 8 KB "Video Utility" ROM with SonyVideo1 BASIC; connections: analogue sound and composite video, RGB (8-pin DIN), keyboard, video interface for the HBI-F900, data recorder, Centronics printer port, two general purpose ports, two cartridge slots, AC power socket and AC plug.
- ↑ 3.0 3.1 3.2 3.3 O MSX Sony HB-F900 que não aceitava cartuchos...– Alexandre Souza, 15 August 2018—link(accessed 2026-10-21) In Portuguese. Repair of an HB-F900 that recognised no cartridge in either the front or the rear slot. The HB-F900 and the HBI-F900 are joined by a 50-pin Centronics cable wired pin to pin, so a Centronics SCSI cable works. The bottom panel comes off to expose the underside of the main board without removing it. The main board is held by six screws plus connectors; removing it completely also means unsoldering a grey coaxial cable to the video output board, so note its connections. The drives are held by four screws at the back; the bar that supports them is commonly bent so the drives sit tilted at the front, and can be removed and straightened; the drives do not use a belt. In his experience the power supply does not normally need recapping. All address, data and control signals to the slots are buffered; with an oscilloscope he found two signals present on the inputs of the buffers and missing on the outputs, and replaced a pair of SN74LS367 chips, fitting them in sockets; he blames a faulty cartridge.
- ↑ 4.0 4.1 4.2 4.3 4.4 Instructions to repair or replace HB-F900 Floppy Drive(s)?, May 2021—link(accessed 2026-10-21) Thread by BitSquad: the HB-F900's drive answers "Disk Offline" to FILES. sdsnatcher73, 12 May 2021: a PC drive converted for MSX with the READY signal works; without it, on an HB-F700, the machine freezes when booting into BASIC until a formatted disk is inserted, while games and DOS boot normally. Manuel, 12 May 2021: Sony machines use the WD2793; if the HB-F900's drive is like the HB-G900P's, it has a standard 34-pin Shugart connector. BitSquad, 13 May 2021: the machine then started with a red screen and did not reach BASIC; Manuel: the stored settings were corrupt, cured with SHIFT+F1, SET TITLE "", SET SCREEN and a reset, which worked; Grauw: the start-up colour is a setting, SET TITLE "",1 gives the blue screen; sdsnatcher73: this happens when the backup battery is low after long disuse and the clock memory is corrupted. BitSquad, 15 May 2021: a new Mitsumi drive lit its LED continuously until the cable was turned round, then answered "Disk Offline"; Manuel: a continuously lit LED means the cable is upside down; meits: bridge pins 33 and 34 to provide READY, without touching pin 32, and one drive is enough; jltursan: on the cable, swap lines 10 and 12 and join 33 and 34 to make a PC drive into drive A with a constant READY. sdsnatcher73, 16 May 2021: a red screen with "@ D" under the logo means the backup battery is dying; remove it. Accumulator, 10 March 2023: a Mitsumi D359T5 worked in an HB-F700.
- ↑ repairBas (Bas Kornalijnslijper), Modificatie dubbelzijdige diskdrive (preventive modification for the double-sided disk drive), PDF, 2010, in Dutch, https://repairbas.file-hunter.com/docs/drives/Preventieve%20modificatie%20dubbelzijdige%20diskdrive.pdf (retrieved 2026-10-21). Lists the drive as used in the Philips NMS 8250, 8255 and 8280, Sony HB-F500P/D/F, HB-T600, HB-F700P/D/F/S, HB-F900, HB-D20W and HBD-30W, Panasonic FS-FD1 and Sanyo MPC-25. For drives that work: tighten the eject mechanism so it does not spring back by itself while a disk is being removed, so the head does not catch on the disk shutter; remove the white part shown and cut away its small nub with a knife, as in the photographs.
- ↑ USB Secret Base, "HB-F900", annotated photograph of the inside (http://usbsecretbase.michikusa.jp/hb-f900/index.html, retrieved 2026-10-21). Read from it: the power supply at the back left with its transformer, heatsinks and a large reservoir capacitor; the speaker at the front left; the DSP board along the back right, with many small electrolytics; the two drives side by side at the front, over the main board.
- ↑ Sony, HB-F900 / HBI-F900 catalogue, Japan, dated '86.10 (October 1986), Internet Archive item sonyhbf900hbif900, page 12, "HB-F900/HBI-F900の主な仕様" (main specifications), and page 3. In Japanese. HB-F900: Z-80A; ROM 192 KB (MSX2 BASIC, MSX2 Disk BASIC and kanji ROM); main RAM 256 KB; video RAM 128 KB; interfaces: two cartridge slots, video, RGB (8-pin), RF, audio, cassette tape, two joystick ports, printer, AC outlet and 50-pin video I/F; accessories include the mouse, a video cable, a plug adapter, an antenna connector and the Wordship software; main unit 355 mm wide × 325 mm deep × 76 mm high, 5.7 kg; keyboard 409 × 183 × 32 mm, 1.2 kg; power 100 V, 50/60 Hz; price ¥148,000. HBI-F900 AV Creator ¥64,800, 100 V, 27 W. Page 3 shows the front panel: power switch, cartridge slot 1, drives A and B with IN USE lamps, reset button, computer sound slider, controller ports A and B, keyboard socket.