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Sony HB-F900 Capacitor Replacement Guide

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Sony HB-F900 main board
HB-F900 main board. Its electrolytics are few; most of the machine's small electrolytics are on the DSP board

No capacitor list or schematic for the Sony HB-F900 has been published, and the values cannot be read in the photographs of its boards that are available.[1][2] The notes below cover what is known about its capacitors and how to record your own board.

What is known

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  • The power supply sits at the back left of the case, with its transformer, heatsinks and a large reservoir capacitor.[3]
  • The DSP board along the back right, which handles the HBI-F900 interface and the video and audio outputs, carries many small electrolytics.[4][3]
  • The main board has only a few electrolytics, with a GS Ni-Cd backup cell (50 mAh, 2.4 V) at the left.[1]
  • The supply board's capacitors are numbered in a C100 series: an owner recapping it in June 2026 could not read the value of C112 and asked for it on the MSX Resource Center forum, without a reply.[5]
  • Alexandre Souza of Tabajara Labs, who has repaired the HB-F900, says its power supply does not normally need recapping.[6]

Sony's European Sony HB-F700 uses the same chipset and has a published capacitor list, in the Sony HB-F700 Capacitor Replacement Guide. The HB-F700 runs from 220 V and has one drive, so its list is no substitute for reading the HB-F900's own boards.[7]

Which to replace first

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General advice on the MSX Resource Center forum is to treat the main power supply's capacitors as worth replacing whatever their condition, to judge audio and video capacitors by the output, and to leave small decoupling capacitors unless there is a reason.[8] On the HB-F900 that means:

  1. The reservoir and output capacitors of the power supply, if any show leakage, bulging or a rail is low or noisy.
  2. The DSP board's capacitors, if the composite, RGB or audio output is poor.
  3. The rest only if they show leakage or bulging.

Recording the board

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  1. Unplug the machine and open it; see the Sony HB-F900 General Maintenance guide.
  2. Photograph each board from above, then each electrolytic close up so the printing on the sleeve can be read.
  3. For each capacitor, write down the designator, capacitance, voltage, diameter and height, and which way the stripe faces.
  4. Order replacements of the same capacitance and at least the same voltage, in a size that fits.
Template for the HB-F900's capacitor list
Ref Value Voltage Diameter × height Board Notes

Procedure

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  1. Replace one capacitor at a time, with the stripe on the same side as the original.[8]
  2. The main board can be worked on from underneath with the bottom panel off; removing it completely means unsoldering a coaxial cable.[6]
  3. Inspect the Ni-Cd backup cell while the boards are exposed, and remove it if it has leaked.[9]
  4. Clean any electrolyte off the board and check the tracks round it.

After the recap

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Check that the machine starts to the MSX logo and BASIC, that both drives read a disk, and that the picture and sound are clean. If the start-up screen is the wrong colour, reset the stored settings as described in the Sony HB-F900 Troubleshooting Guide.[10]

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References

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  1. ↑ 1.0 1.1 File:Sony HB-F900 main board.jpg, photograph of the main board of a black HB-F900, uploaded to the MSX Resource Center wiki by Gdx on 20 March 2016. Read from it: Yamaha V9938, Sharp LH0080 Z80, WD2793A-PL floppy controller, and at the left a GS sealed Ni-Cd battery labelled 50 mAh, 2.4 V (Japan Storage Battery Co.). The values of the electrolytic capacitors cannot be read in the photograph.
  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.
  3. ↑ 3.0 3.1 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.
  4. ↑ HB-F900, USB Secret Base (up-c)—link(accessed 2026-10-21) In Japanese. Specification list (Z80A at 3.57 MHz, 256 KB RAM, 128 KB VRAM with the V9938, JIS level 1 kanji ROM, MSX-JE not fitted, PSG equivalent to the AY-3-8910, two 3.5-inch 2DD drives, two cartridge slots, MSX-BASIC 2.0 and Disk BASIC 1.0) and annotated photographs. Front panel: power switch, power lamp, slot 1, reset switch, drives A and B, volume slider, joystick ports A and B, keyboard connector. Rear panel: RF channel switch, RF output, video output, audio output, RGB output, HBI-F900 interface connector, slot 2, earth terminal, printer connector, data recorder interface, AC outlet (AC 100 V), mains lead. Inside: the power supply section, the speaker, the DSP board (interface to the HBI-F900 and video and audio output), the main board and drives A and B.
  5. ↑ Sony HB-F900 Power Supply Capacitor, 8 June 2026—link(accessed 2026-10-21) Post by MikeB: replacing the capacitors in an HB-F900 power supply, he could not read the value of C112 and asked for its capacitance and voltage. No reply when retrieved.
  6. ↑ 6.0 6.1 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.
  7. ↑ 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.
  8. ↑ 8.0 8.1 Recap recommendations, June 2018—link(accessed 2026-10-21) Reply by RetroTechie, 23 June 2018: in an MSX, electrolytics used for supply bypassing can often be removed without the machine stopping, those in the audio and video circuits show their condition in the output, and those in the main power supply are worth replacing whatever their condition; use the service manual's parts list where there is one, compare it with the board, and replace one capacitor at a time.
  9. ↑ Diagnostic on dead Sony HB-F700F, 2015–2017—link(accessed 2026-10-21) gdx, 8 November 2016: replace a rechargeable backup cell with the same type (Ni-Cd) and fit it in a holder rather than soldering to it, so a later leak stays in the holder; l_oliveira, 6 November 2016: a dead battery will not stop an MSX booting unless the clock's power circuit is faulty; sd_snatcher, 28 October 2016: a battery fault stopped an NMS 8245 booting.
  10. ↑ 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.


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