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Sony HB-10 General Maintenance

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Sony HB-10P disassembly (service manual)
Opening the HB-10P: the five case screws, the upper case lifted back, the keyboard tape cable and the PU-37 board under its shield plate (Sony service manual, page 2-1)

Routine work on the Sony HB-10 MSX computer covers opening the case, removing the keyboard, checking the AC adaptor and the supply rails, and the one adjustment in Sony's service manual. The steps and part references come from Sony's service manual for the European HB-10P and HB-10B.[1] Niga, who repaired and modified a Japanese HB-10, reports that its board is the same design as the PAL board, so most of this applies to the Japanese model too.[2]

Before you start

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The computer itself runs on low voltage. Mains voltage is present only inside the AC adaptor, which holds the transformer, its fuses and the rectifier for the DC output.[3] Unplug the adaptor from the wall before opening it. Its fuses, transformer and mains cord are marked in the manual as critical to safety, to be replaced only with the parts listed.[3]

Do not plug in or pull out a cartridge with the power on. The MSX Resource Center warns that doing so can damage the machine.[4]

Opening the case

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Sony's procedure for the HB-10P and HB-10B:[5]

  1. Disconnect the adaptor and any cartridges and cables.
  2. Turn the computer over and remove the five case screws.
  3. Lift the upper case and swing it back as shown in the drawing.
  4. Pull the keyboard's tape cable out of its connector on the main board.
  5. To take the PU-37 board out, remove the screw in the bottom cabinet, the three screws holding the shield plate and the nine screws holding the board.
  6. Disconnect CN2 and remove the screw that holds IC1, the 5 V regulator.
  7. Lift the board out in the direction of the arrow in the drawing.

The RF modulator is part of the board assembly. The HB-10P and HB-10B use different modulators (MDG-UE3622 and MDG-UB3622), so a replacement PU-37 board for an HB-10B needs the HB-10B modulator fitted.[5]

sd_snatcher, writing on the MSX Resource Center forum, warns that this board has very fragile tracks. To remove a part, cut its leads, melt the solder on each pad and pull the remains out with pliers before cleaning the holes.[6]

Removing the keyboard

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  1. With the upper case off, remove the six screws that hold the keyboard unit and lift it out.
  2. Remove the 21 screws that hold the key switch unit to the keyboard frame to reach the switch film.

[5]

Cleaning

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With the board and keyboard out, the upper and lower cases can be washed in warm water with a little washing-up liquid and left to dry completely before reassembly. Clean the cartridge slot contacts and the edge of each cartridge with isopropyl alcohol. Dust the board with a soft brush and look for corrosion and leaked electrolyte in the power section, around the adaptor socket CN11, the 10,000 µF reservoir C1 and the regulators (grid squares A-13 to E-11 on Sony's board drawing).[7]

Checking the AC adaptor

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Every AC-HB1 version gives two outputs: DC 6 V at 900 mA and AC 16 V at 160 mA. The input voltage and plug depend on the market (100 V for the Japanese AC-HB1, 240 V for the AC-HB1B, 220 V for the AC-HB1D and AC-HB1P).[8] The connector is Sony's own, and the AC-HB3 cannot stand in for it.[8] Niga notes that the adaptor for Panasonic's first FS-A1 looks similar but differs in voltage and size.[2]

AC-HB1P and AC-HB1B outputs and fuses (Sony service manual)
Output Rating Made by Fuse in the adaptor
DC 6 V, 900 mA Centre-tapped winding, D1 and D2 (RU-4A), C1 (330 µF 25 V) and C2 (0.33 µF) F1 and F2, T1.25A 250 V, one in each side of the winding
AC 16 V, 160 mA Separate winding F3, T200mA 250 V

[8][3]

The transformer also has a 133 °C thermal fuse in its primary. It is drawn inside the transformer, and Sony supplies the transformer only as an assembly with its mains cord.[3] If the adaptor gives no output at all and its fuses are intact, check continuity across the pins of the mains plug. With the cord intact, an open circuit there means the primary winding or the thermal fuse in series with it is open.

If the original adaptor is missing, Niga ran his Japanese HB-10 on a 5 V USB supply wired to the board's 5 V side, and notes that the ±12 V rails feed only the cartridge slots.[2]

Supply rails on the board

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The PU-37 board makes three rails from the adaptor's two outputs.[9] Measure across the capacitors, which are easier to reach than the regulator pins.

PU-37 supply rails (HB-10P and HB-10B)
Rail Regulator Fed from Measure across
+5 V IC1, µPC7805, on a heatsink DC input through S901 to C1 (10,000 µF 25 V) C35 (470 µF) or C28 (47 µF)
+12 V IC19, µPC78L12 AC input through D2 (10E2) to C4 (220 µF 35 V) C29 (47 µF)
−12 V IC20, µPC79L12 AC input through D1 (10E2) to C3 (220 µF 35 V) C30 (47 µF)

[9]

Sony's manual gives no tolerance for the rails. If +5 V is low, measure the unregulated voltage across C1 before condemning the regulator, then look for a heavy load on the board. The Sony HB-10 Troubleshooting Guide goes through this.

The 5 V regulator is screwed to a heatsink.[5][2] sd_snatcher recommends a good thermal compound between them.[6] Niga found the video chip runs warm and fitted a heatsink to it.[2]

Clock adjustment

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The only adjustment in the HB-10P/10B manual sets the video clock:[10]

  1. Switch the computer on.
  2. Connect a frequency counter to pin 38 of IC5, the T6950 video chip.
  3. Turn trimmer capacitor CV1 until the counter reads 22.168 MHz ±10 Hz.

The adjustment drawing shows CV1 just below IC5 on the component side.[10] Leave CV1 alone unless a frequency counter shows the clock is outside that tolerance.

Capacitors

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The board's electrolytic capacitors, with Sony's values, are listed in the Sony HB-10 Capacitor Replacement Guide. Signs of a failing capacitor are covered in Capacitor Failure Symptoms.

Things that are not faults

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  • On a Japanese 16 KB HB-10, MSX-BASIC reports 12,431 bytes free. After Niga's 64 KB upgrade it reported 28,815 bytes.[2]
  • On the 64 KB versions, the top 16 KB of RAM also appears in slot 0. This is the port A8h mirror, a design quirk described in the Sony HB-10 Troubleshooting Guide.[4]
  • The T6950 video chip in the European versions does not support some undocumented features of Texas Instruments' TMS9918 family.[4]

Maintenance checklist

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  1. Check that the adaptor is the right AC-HB1 version for the local mains voltage.[8]
  2. Measure the adaptor's DC and AC outputs, and check F1, F2 and F3 if either is missing.
  3. Open the case and look at the power section for leaking or bulging capacitors and for corrosion.
  4. Check +5 V, +12 V and −12 V across C35, C29 and C30.
  5. Clean the cartridge slot contacts and check that the keyboard tape cable is fully home.
  6. On a European machine, if you have a frequency counter, check the 22.168 MHz clock at IC5 pin 38.
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References

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  1. ↑ Sony, HB-10P/10B, AC-HB1P/HB1B Service Manual, part no. 9-975-599-01, 1985 (File:Sony HB-10P HB-10B Service Manual 9-975-599-01.pdf). Hosted with a description at Sony HB-10P and HB-10B Service Manual.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 SONY HB-10の補修と改造– Niga, にがMSX—link(accessed 2026-10-21) Repair and modification of a Japanese HB-10.
  3. ↑ 3.0 3.1 3.2 3.3 Sony, HB-10P/10B service manual (File:Sony HB-10P HB-10B Service Manual 9-975-599-01.pdf), AC adaptor schematic on page 5-17 and parts list on page 7-9: T1 with a 133 °C thermal fuse in the primary, F1 and F2 T1.25A 250 V, F3 T200mA 250 V, D1 and D2 RU-4A, C1 330 µF 25 V, C2 0.33 µF 50 V film, C3 and C4 0.022 µF 50 V ceramic; T1 is supplied only with its mains cord, 9-988-564-01 for the AC-HB1B and 9-988-550-01 for the AC-HB1P.
  4. ↑ 4.0 4.1 4.2 Sony HB-10, MSX Resource Center wiki—link(accessed 2026-10-21) Series page: models, slot maps, the port A8h RAM mirror and its fix, the 16 KB to 64 KB upgrade, the PSG resistor change, and the warning not to insert a cartridge with the power on.
  5. ↑ 5.0 5.1 5.2 5.3 Sony, HB-10P/10B service manual (File:Sony HB-10P HB-10B Service Manual 9-975-599-01.pdf), disassembly, pages 2-1 and 2-2.
  6. ↑ 6.0 6.1 Sony HB10 / HB20 Hardware issue + fix, MSX Resource Center forum, 11 March 2017 to 30 May 2020—link(accessed 2026-10-21) sd_snatcher, 9 April 2017: the board has very fragile tracks, so cut component leads and remove them pad by pad; apply good thermal paste to the 7805.
  7. ↑ Sony, HB-10P/10B service manual (File:Sony HB-10P HB-10B Service Manual 9-975-599-01.pdf), PU-37 board drawings on pages 5-8 and 5-9 and location list on page 5-10: C1 at B-13, C3 at D-12, C4 at C-12, C28 at D-13, C29 at C-11, C30 at D-12, C35 at E-11, IC19 at C-12, IC20 at D-12, inlet CN11 at A-13, CV1 at G-12, IC5 at E-12.
  8. ↑ 8.0 8.1 8.2 8.3 Sony AC-HB1, MSX Resource Center wiki—link(accessed 2026-10-21) Adaptor versions by region, proprietary connector, outputs DC 6 V 900 mA and AC 16 V 160 mA, not interchangeable with the AC-HB3.
  9. ↑ 9.0 9.1 Sony, HB-10P/10B service manual (File:Sony HB-10P HB-10B Service Manual 9-975-599-01.pdf), PU-37 schematic, page 5-12: CN11 (DC IN, AC IN, GND), S901, C1 10000 µF 25 V and IC1 µPC7805 for +5 V with C28 and C35 on the output; D2, C4 and IC19 µPC78L12 for +12 V with C29; D1, C3 and IC20 µPC79L12 for −12 V with C30.
  10. ↑ 10.0 10.1 Sony, HB-10P/10B service manual (File:Sony HB-10P HB-10B Service Manual 9-975-599-01.pdf), alignment, page 6-1: power on, frequency counter on pin 38 of IC5, adjust CV1 for 22.168 MHz ±10 Hz.


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