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Sony HB-F700 General Maintenance

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Sony HB-F700S inside
Inside an HB-F700S: transformer and power supply board at the left, the video board with the V9938 at the right, the drive at the front right

The Sony HB-F700 is a desk-top MSX2 from 1986 with a separate keyboard, a built-in 3.5-inch drive and a linear power supply inside the case, running from 220 V or 240 V mains.[1] Sony's service manual for the HB-F700P, F700S, F700F and F700D is hosted here as the Sony HB-F700 Service Manual, and the procedures below follow it. The repair reports cited are from owners on the MSX Resource Center forum.

Mains safety

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  • The transformer primary, the fuse F901 (T630 mA), the line filter coil L901 and the power switch S901 all carry mains voltage. Unplug the machine before taking the cover off. The manual marks the fuse, the switch, the transformer and the mains lead as safety-critical parts, to be replaced only with the part numbers it lists.[2][3][4]
  • The front switch is labelled ON/STANDBY. It is a push switch in the transformer primary, listed as the AC power switch S901.[5][2][3] Unplug the mains lead anyway before working inside.
  • The HB-F700P is rated at 220 V AC, 50/60 Hz, and the HB-F700B at 240 V AC, 50/60 Hz, both drawing 42 W.[1]

Opening the case

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The manual begins with "remove the case" and does not show the case screws, so note where each screw comes from as you take them out. Once the cover is off, the parts come away in this order:[6]

  1. Cartridge holder: remove its two BVTT 3 × 8 mm screws and lift the holder out, then the EX-119 board behind it.
  2. DUS board, the video board on top of the chassis: remove its BVTT 3 × 6 mm screws and lift it off.
  3. Front panel: remove the BVTT 3 × 6 mm screws and the connector cover, then the front panel assembly.
  4. Main board: turn the machine over, loosen the BVTT 3 × 6 mm screws holding the bottom plate and take the plate off. Remove the BVTT 3 × 6 mm screws holding the main board.
  5. Floppy drive: remove its BVTT 3 × 6 mm screw, pull up the connectors and lift the drive unit out.

Owners describe the video board as fragile. One advises checking the solder joints round the video RAM, because the board is not epoxy glass and breaks easily.[7] Support it while it is out.

Keyboard

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The keyboard is a separate unit on a cable to the front KEYBOARD socket.[5] On an HB-F700D stored for about 25 years, the space bar, X, M, CTRL, the cursor keys and sometimes 3 worked only when pressed very hard. These keys are not on one row or column of the matrix, which pointed away from the wiring. The keyboard was full of dirt. Brushing the board with a soft brush and cleaning each conductive track and each key's conductive dome cured it, without any liquid.[8]

Cartridge slots

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Insert and remove cartridges only with the power off. An experienced member of the MSX Resource Center warns that the HB-F700's video processor "doesn't like" a cartridge being plugged in while the machine is on.[9] Clean the cartridge's edge contacts before blaming a slot.

Backup battery

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The clock and its settings are kept by a rechargeable Ni-Cd cell, BT1, listed as type GB50H (Sony part 1-528-171-11).[3] An HB-F700F owner describes his as a sealed Ni-Cd battery, 50 mAh, 2.4 V, and found it had started to leak.[9]

  1. Inspect BT1 every time the case is open. Look for white or green crust on the cell and on the board round it.
  2. If it has leaked, remove it and clean the tracks underneath. Follow Battery Explosion, Capacitor or Corrosion Damage for the cleaning.
  3. Replace it with a rechargeable Ni-Cd cell of the same type as the original. One member advises mounting the new cell in a holder, so that a later leak stays in the holder and off the board.[9]

Members disagree on whether a dead or missing battery can stop the machine starting. One reports an MSX that would not boot with a bad battery; another says a missing battery should not stop it booting unless the clock's power circuit itself is damaged.[9]

Floppy drive

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The drive is a double-sided 3.5-inch unit, formatted to 720 KB, turning at 300 rpm.[1] Do not take a disk out, or switch to standby, while the IN USE lamp is lit.[5] For cleaning and general drive work see Floppy Drive Repair.

repairBas (Bas Kornalijnslijper) lists the HB-F700P, D, F and S among the machines that use the same double-sided drive as the Philips NMS 8250 and the Sony HB-F500 and HB-F900. His preventive modification, for drives that still work, stiffens the eject mechanism so that it does not spring back while a disk is being withdrawn, which can catch the head on the disk's shutter. The change is to remove a small white plastic part and cut away its small nub with a knife, as his photographs show.[10]

If the original drive has to be replaced, one owner reports that a Mitsumi D359T5 worked in an HB-F700. A PC drive must provide the READY signal: without it, a converted drive in an HB-F700 froze the machine on booting into BASIC until a formatted disk was inserted.[11]

Supply rails

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The PS-133 board has three linear regulators fed from the transformer. Measure the input and output of each against ground with the machine running:[2]

HB-F700 regulators (service manual, page 40)
Rail Regulator Input (marked on the schematic) Output
+5 V IC902, SI3052V (pin 3 in, pin 1 ground, pin 2 out) 9.3 V 5 V
+12 V IC901, SI3122V (pin 3 in, pin 1 ground, pin 2 out) 18.2 V 12 V
−12 V IC903, NJM79L12A (pin 2 in, pin 3 ground, pin 1 out) 19.1, on the negative side −12 V
+9 V (video board) IC307, NJM78M09A about 12 V about 9 V

The figures for IC307 are from owners' measurements; the 9 V regulator is on the video board near the RGB socket.[7][8] Sony's notes say its voltages were read with a 50 kΩ/V meter under no-signal conditions and will vary between machines.[4] A rail that is missing at the regulator output but present at its input points to the regulator; a low input points to the transformer, the rectifiers or the reservoir capacitor. The Sony HB-F700 Troubleshooting Guide goes through each case.

Electrolytic capacitors

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The largest electrolytics are the supply reservoirs: C909 (22000 µF 16 V) for +5 V, C905 (10000 µF 25 V) for +12 V and C912 (470 µF 35 V) for −12 V.[2] The video board has a row of five large electrolytics behind the rear sockets.[12] One owner recapped the whole top board and his machine stayed dead, so do not expect a recap to cure every fault.[9] The full list from Sony's parts list is in the Sony HB-F700 Capacitor Replacement Guide.

Adjustments

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Sony's adjustments need a frequency counter and an oscilloscope. Leave the presets alone unless a symptom points to one of them.[13]

HB-F700 adjustments (service manual, pages 25 and 26)
Adjustment Where to measure Specification Adjust
CPU clock IC301 pin 8, DUS-135 board 3,579,540 to 3,579,549 Hz CV301
Timer (clock chip) TP4, PU-53 board, with a 100 kΩ pull-up from TP4 to +5 V and the test program running 15.9999 to 16.0001 Hz CV1
RGB level, red CN309 pin 6, DUS-135 board, white screen 0.7 ± 0.02 V RV302
RGB level, green CN309 pin 7 0.7 ± 0.02 V RV303
RGB level, blue CN309 pin 8 0.7 ± 0.02 V RV301
Floppy controller VCO TP3, PU-53 board, TP1 grounded, three minutes after switch-on 250 ± 1 kHz RV2
Read pulse width TP2, PU-53 board, TP1 grounded 0.5 µs ± 10 ns RV1

For the RGB adjustment, connect an RGB monitor or terminate pins 6, 7 and 8 of CN309 in 75 ohms. Remove the jumper from TP1 after the floppy controller adjustments. The manual's test program is headed "for HB-F5/F500" and drives the clock chip through I/O ports B4h and B5h. These three lines from it set and cancel the 16 Hz test output on TP4:[13] 

200 OUT &HB4,14:OUT &HB5,0
210 OUT &HB4,15:OUT &HB5,8:'Timer Clock adj.(set)
240 OUT &HB5,12:'Timer Clock adj.(reset)
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References

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  1. ↑ 1.0 1.1 1.2 Sony, Service Manual HB-F700P/F700S/F700F/F700D, pages 1 and 2, "Specifications". See Sony HB-F700 Service Manual. Z80A at 3.58 MHz; ROM 64 KB; RAM 256 KB; VRAM 128 KB; V9938; 90-key KBD-12P keyboard; composite video on the 6-pin DIN socket 1 V p-p black and white; RGB 0 to 0.7 V into 75 ohms on an 8-pin DIN; 3.5-inch double-sided drive, 720 KB formatted, 300 rpm; 220 V AC 50/60 Hz (HB-F700P), 240 V AC 50/60 Hz (HB-F700B); 42 W for the main unit; resetting automatic at power-on or manual, "memory contents are not maintained".
  2. ↑ 2.0 2.1 2.2 2.3 Sony, Service Manual HB-F700P/F700S/F700F/F700D, page 40, schematic diagram, PS-133 board. See Sony HB-F700 Service Manual and File:Sony HB-F700 PS-133 power supply schematic.png. Transformer T901; primary through the power switch, fuse F901 and line coil L901, with C911 and C915 (0.022 µF 250 V) and C906 (2200 pF 400 V). +5 V: bridge D904 (D5FB20F), reservoir C909 22000 µF 16 V, regulator IC902 SI3052V (input pin 3, 9.3 V marked; ground pin 1; output pin 2, 5 V), output capacitor C904 100 µF 10 V, C902 0.33 µF. +12 V: D901 and D903 (U05G), reservoir C905 10000 µF 25 V, IC901 SI3122V (input pin 3, 18.2 V marked; ground pin 1; output pin 2, 12 V), C903 100 µF 16 V, C901 0.33 µF. −12 V: D902 (10E2N), reservoir C912 470 µF 35 V, IC903 NJM79L12A (input pin 2, 19.1 marked; ground pin 3; output pin 1, −12), C907 100 µF 16 V, C908 0.33 µF. Power LED D905 (TLG124A) on the LE-50 board.
  3. ↑ 3.0 3.1 3.2 Sony, Service Manual HB-F700P/F700S/F700F/F700D, pages 76 to 80, section 8, "Electrical Parts List". See Sony HB-F700 Service Manual. Boards PU-53 (PR-53 on the F and S models), DUS-135, CN-149, CN-150, CN-151, PS-133, LE-50 and EX-119; BT1 1-528-171-11, battery, storage, Ni-Cd (GB50H); IC307 NJM78M09A; IC901 SI3122V; IC902 SI3052V; IC903 NJM79L12A; F901 fuse T630 mA (1-532-284-11, marked as safety-critical); S901 push switch (AC power); T901 power transformer 1-448-626-11.
  4. ↑ 4.0 4.1 Sony, Service Manual HB-F700P/F700S/F700F/F700D, page 59, notes to the schematic diagrams. See Sony HB-F700 Service Manual. Capacitor values in µF unless marked; voltages are DC with respect to ground, taken under no-signal conditions with a 50 kΩ/V meter, and vary with production tolerances; parts marked with the shaded warning symbol are critical for safety and must be replaced with the part number specified.
  5. ↑ 5.0 5.1 5.2 Sony, Service Manual HB-F700P/F700S/F700F/F700D, pages 3 and 4, "Location and Function of Parts". See Sony HB-F700 Service Manual. Front: ON/STANDBY switch and indicator, cartridge slots 1 and 2, disk eject button, RESET button (resets the computer; "the internal memory will then be erased"), controller connectors A and B, keyboard connector, IN USE lamp (do not remove the disk or switch to standby while it is lit). Rear: TAPE (8-pin DIN), AUDIO/VIDEO output (6-pin DIN; "Video signals from this connector are black-and-white"), RGB (8-pin DIN, for a colour monitor with a 21-pin RGB input), ground terminal, PRINTER (14-pin), EXT DRIVE (34-pin, for a second drive such as the Sony HBD-30W).
  6. ↑ Sony, Service Manual HB-F700P/F700S/F700F/F700D, pages 21 and 22, section 4, "Disassembly". See Sony HB-F700 Service Manual. Starting from "remove the case": cartridge holder (two BVTT 3 × 8 screws, the holder, then the EX-119 board); DUS board (BVTT 3 × 6 screws, then the board); front panel (BVTT 3 × 6 screws, the connector cover, then the front panel assembly); main board (loosen the BVTT 3 × 6 screws, remove the bottom plate, then the BVTT 3 × 6 screws and the main board); floppy drive unit (BVTT 3 × 6 screw, pull up the connectors, lift the unit out). Pages 23 and 24 cover the drive motor and head block.
  7. ↑ 7.0 7.1 Sony HB-F700S with problems, March 2016—link(accessed 2026-10-21) Thread by Pablibiris about an HB-F700S with no picture. RetroTechie, 13 March 2016: IC307 (78M09) near the RGB connector should have about 12 V on its input pin, ground on the middle pin and about 9 V on its output, which feeds the R, G, B and sync output circuits; if the 9 V fails, RGB and A/V output are lost. Pablibiris, 14 March 2016: two boards, an upper one with the RGB and tape connections and a lower motherboard; replacing IC307 brought the picture back, after which graphics were corrupted and the boot screen reported 64 KB of VRAM. Wierzbowsky, 15 March 2016: most MSX2 machines have 128 KB of VRAM, so a 64 KB report points to the VRAM chips or their connection to the VDP; trace CAS0 and CAS1 from the VDP to the pairs of VRAM chips. Pablibiris, 15 March 2016: photographs of a strange cursor and garbled characters and graphics; the TESTRAM program passed the RAM but restarted the machine during the VRAM test; changing all the memory did not help; fitting a complete replacement video board did, and he suggests the VDP may have been broken. Jipe, 15 March 2016: check the solder joints on the VRAM; the board in the HB-700 breaks easily because it is not epoxy.
  8. ↑ 8.0 8.1 on repairing a Sony HB-F700 to checkout FD50, 13 October 2025—link(accessed 2026-10-21) Post by Pat about an HB-F700D after about 25 years in storage: no video or sound on two cables; the drive light came on at switch-on and reset and the Caps Lock light could be toggled; the supply lines from the power supply to the main board were normal; on the video board, which sits on top, the 9 V regulator IC307 had 12 V on its input and almost nothing on its output, and measured 2.5 or 4.5 kΩ from output to ground with the power off; replaced with an LM7809, after which the MSX logo appeared. Several keys (space, X, M, CTRL, the cursor keys and sometimes 3) were unreliable and are not on one row or column of the matrix; the keyboard was full of dirt, and brushing the board and cleaning each conductive track and key dome cured it without any fluid. Links repairBas's video "No RGB and Video Signal on a Sony HB-F700P/D MSX 2 Computer".
  9. ↑ 9.0 9.1 9.2 9.3 9.4 Diagnostic on dead Sony HB-F700F, 2015–2017—link(accessed 2026-10-21) Thread by Louthrax about an HB-F700F that showed nothing and gave no Caps Lock response. gdx, 1 March 2015: failed electrolytics are often swollen on top, replace any that is even slightly concave; old solder joints age badly, resolder them with flux; "The VDP of HB-700 doesn't like" a cartridge inserted with the power on. RetroTechie, 2 March 2015: no Caps Lock response usually means the CPU gets no clock (a dead VDP can cause that) or something stops the Z80, ROM or RAM; test with a known good RAM cartridge and a cartridge that plays sound at power-on, with a speaker on the audio output. l_oliveira, 3 March 2015: check power, then clocks, then the tracks, then the VDP, ROM, RAM and CPU; a VRAM fault spoils the picture but does not stop the machine starting. Louthrax, 28 October 2016: the top board had been recapped without effect; the backup battery had started to leak and was removed and the tracks cleaned; he describes it as a sealed Ni-Cd battery, 50 mAh, 2.4 V. sd_snatcher, 28 October and 6 November 2016: a battery fault stopped an NMS 8245 booting; the main ROM is IC5, a 32 KB 28-pin part that can be socketed and replaced with an MSX1 BIOS for a test. l_oliveira, 6 November 2016: a dead battery will not stop the machine booting unless the clock's power circuit is faulty. Eugeny_Brychkov, 6 November 2016: with a multimeter, measure the voltage on the CPU's pin 26 (reset) and pin 6 (clock) with the machine switched on. gdx, 8 November 2016: a turbo R would not boot with drained batteries; replace a rechargeable cell with the same type (Ni-Cd) and fit it in a holder rather than soldering to it. Louthrax, 15 June 2017: all motherboard capacitors changed and the board still dead; it was passed to another member for repair.
  10. ↑ 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.
  11. ↑ 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.
  12. ↑ File:Sony HB-F700S inside.jpg, photograph of an HB-F700S with the top cover off, uploaded to the MSX Resource Center wiki by Gdx on 15 April 2016. Read from it: the transformer at the front left; the power supply board behind it with a fuse, a D5FB20 bridge and a large reservoir capacitor, under a heatsink along the back panel; the upper board with the V9938, a row of five large electrolytic capacitors behind the rear DIN sockets, resistors R352 to R355 and three blue presets in front of them, and a relay at the back right.
  13. ↑ 13.0 13.1 Sony, Service Manual HB-F700P/F700S/F700F/F700D, pages 25 and 26, section 5, "Adjustments". See Sony HB-F700 Service Manual. BASIC adjusting program headed "CHECK PROGRAM for HB-F5/F500": W key, white screen for the RGB level adjustment; S key sets the timer clock output (lines 200 and 210: OUT &HB4,14:OUT &HB5,0 and OUT &HB4,15:OUT &HB5,8); R key cancels it (line 240: OUT &HB5,12). Connect a KX-14CP1 monitor to CN309 or terminate pins 6, 7 and 8 of CN309 in 75 ohms. CPU clock: IC301 pin 8 on the DUS-135 board, 3,579,540 to 3,579,549 Hz, adjust CV301. Timer clock: 100 kΩ pull-up from TP4 to +5 V, TP4 on the PU-53 board, 15.9999 to 16.0001 Hz, adjust CV1. RGB levels: 0.7 ± 0.02 V from sync level to colour level at CN309 pin 6 (red, RV302), pin 7 (green, RV303) and pin 8 (blue, RV301). Floppy controller, three minutes after switch-on with TP1 grounded by a jumper: VCO frequency 250 ± 1 kHz at TP3, adjust RV2; read pulse width 0.5 µs ± 10 ns at TP2, adjust RV1; remove the jumper afterwards.


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