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Sony HB-75 General Maintenance

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Sony HB-75P inside
An HB-75P with the upper cabinet off. The transformer is at the rear left and the power board sits over the shield at the rear.

Routine work on the Sony HB-75 series follows Sony's service manual for the European HB-55P, HB-75P and HB-75B. The Japanese HB-75 runs on 100 V and has a different rear panel, and the manual does not cover it.[1][2]

Safety

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The HB-75P and HB-75B take mains directly: 220 V or 240 V into a fuse board, the power switch and a transformer inside the case.[1][3] Unplug the machine before opening it. Sony marks the 4700 pF, 400 V ceramic capacitor across the power switch (C9 on the fuse board) as critical to safety; replace it only with the same type.[4][5] The transformer has a thermal fuse in its primary winding; if the transformer has overheated, check the primary for continuity.[3]

Opening the case

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From Sony's service manual:[5]

  1. Unplug the mains lead.
  2. Remove the three screws in the lower cabinet.
  3. Lift the upper cabinet enough to unplug CN11 (13-pin) and CN12 (9-pin) from the main board and CN2 (2-pin) from the power board.
  4. Release the three hooks and lift the upper cabinet away.

To take out the main board, remove the four screws holding the heat sink, the three main board screws and the two screws in the blind plate, then unplug CN10 (8-pin), which carries the supply rails from the power board.[5][3]

On the HB-75P and HB-75B the function and cursor keytops are not locked into the keyboard. Before handling the keyboard on its own, take it out and tape those keys in place so that they do not fall out.[5]

Power supply

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The supply is linear. The transformer feeds a bridge rectifier and reservoir capacitor for +5 V, two diodes and a reservoir for +12 V, and two more diodes and a reservoir for −12 V. The +5 V regulator (SI-3052V) and +12 V regulator (SI-3122V) are on two small boards of their own, each with a 47 µF output capacitor and a 0.33 µF film capacitor; the −12 V regulator (NJM79L12A) is on the power board.[3][4] The rails reach the main board through CN10 and can be checked at any cartridge slot: +5 V on pins 45 and 47, +12 V on pin 48 and −12 V on pin 50, against pin 41.[3][6]

The electrolytics on the two regulator boards have burst on at least one HB-75P, and the MSX Resource Center lists the model for failure-prone capacitors on small separate boards.[7][8] Check those boards whenever the case is open. Values and replacement are in the Sony HB-75 Capacitor Replacement Guide.

Adjustments

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The manual's alignment covers the PAL encoder and, on the HB-75P and HB-75B, the RGB outputs. Make them in order, and only when a fault calls for it:[9]

Alignment (HB-75P and HB-75B)
Adjustment Test point Specification Control
VCO phase TP1, junction of R37 and R38 7.0 V ±0.1 V VC1
Subcarrier frequency TP2, junction of C28 and C47 4.433618 MHz ±10 Hz VC2
Video output level TP3, pin 2 of CN1 on the power board, into 75 Ω 1 V ±0.1 V p-p VR4
Blue level TP4, pin 3 of CN3 (RGB) 0.7 V ±0.1 V p-p VR1
Red level TP5, pin 15 of CN3 0.7 V ±0.1 V p-p VR2
Green level TP6, pin 11 of CN3 0.7 V ±0.1 V p-p VR3

For the level adjustments, run COLOR 15,15 from BASIC so that the screen is white, and load only the output being measured.[9]

Connectors

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Cracked solder joints on the SCART, DIN and joystick connectors cause flickering video and crackling sound when a lead is moved. Reflow them.[8]

Checklist

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  1. Open the case and look at both regulator boards and the reservoir capacitors for bulging or leakage.
  2. Measure the three rails at a cartridge slot.
  3. Test both cartridge slots, both joystick ports and every key.
  4. Check the composite, RGB and RF outputs with a white screen.

For faults see the Sony HB-75 Troubleshooting Guide.

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References

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  1. ↑ 1.0 1.1 Sony, HB-55P/75P/75B Service Manual, PDF page 3 (printed pages 1-1 and 1-2), features and specifications: Z80A at 3.579545 MHz with one wait state in each M1 cycle; HB-75P/75B 64 KB RAM, HB-55P 16 KB; 48 KB ROM (MSX-BASIC 32 KB, utility program 16 KB); TMS9929ANL video; PAL composite video 1 V p-p, analogue RGB 0 to 0.7 V on the HB-75P/75B, RF on UHF channel 36; audio −5 dBs; 74 keys on the HB-75P/75B; cassette 1200/2400 baud; 14-pin printer port; two 9-pin joystick ports; two MSX cartridge slots; 220 V ±10 %, 50/60 Hz (HB-55P/75P) or 240 V ±10 %, 50/60 Hz (HB-75B); 24 W; about 405 × 67 × 245 mm and 3.5 kg. Hosted here as Sony HB-55P, HB-75P and HB-75B Service Manual.
  2. ↑ Category:Sony HB-75, MSX Resource Center wiki—link(accessed 2026-10-21) The HB-75 series: HB-75 (Japan, 100 V, one cartridge slot plus an expansion bus, RF and composite outputs, black or white, ¥69,800), HB-75AS (Australia, 240 V), HB-75B (UK, 240 V, £299), HB-75D (Germany, 220 V, QWERTZ), HB-75F (France, 220 V, AZERTY, RGB SCART only) and HB-75P (Europe, 220 V); the export models have two cartridge slots, RGB on SCART and composite video and audio on a 6-pin DIN; 1984; 64 KB RAM in slot 2, 16 KB VRAM; TMS9918ANL (HB-75) or TMS9929A (others); PSG AY-3-8910A or YM2149F; NEC D780C-1 Z80A; built-in Personal Databank; the Japanese HB-75 came with the HBI-55 data cartridge; links to Sony's HB-55P/75P/75B service manual on the MSX Archive.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Sony, HB-55P/75P/75B Service Manual, PDF pages 54 and 55 (printed 5-23 and 5-24), schematic of the fuse, LED, power, transformer, +5 V and +12 V boards: mains through fuse F401 (T160mA) and power switch S401, with C9 (4700 pF) across the switch, to transformer T401, which has a thermal fuse in its primary and taps for 220 V (AE) and 240 V (UK); +5 V from bridge D6 (RB-402), reservoir C1 (10,000 µF 16 V) and regulator IC1 (SI-3052V) on the +5 V board with C10 (0.33 µF) and C6 (47 µF 16 V), then L1 (22 µH) and C4 (47 µF 16 V); +12 V from D1 and D2 (10E-2), C2 (3300 µF 25 V) and IC2 (SI-3122V) on the +12 V board with C11 (0.33 µF) and C7 (47 µF 16 V); −12 V from D3 and D4 (10E-2), C3 (330 µF 35 V) and IC3 (NJM79L12) with C5 (0.33 µF) and C8 (47 µF 16 V); +5 V, +12 V and −12 V go to main board connector CN10; the power board also carries the RF unit and the 6-pin audio/video DIN socket. Hosted here as Sony HB-55P, HB-75P and HB-75B Service Manual.
  4. ↑ 4.0 4.1 Sony, HB-55P/75P/75B Service Manual, PDF page 76 (printed 7-14), electrical parts list for the fuse, LED, power, +5 V and +12 V boards: C1 1-125-375-11 electrolytic (block) 10,000 µF 16 V; C2 1-125-376-11 electrolytic (block) 3300 µF 25 V; C3 1-123-362-00 electrolytic 330 µF 50 V; C4, C6, C7 and C8 1-123-332-00 electrolytic 47 µF 25 V; C5, C10 and C11 1-136-171-00 film 0.33 µF 50 V; C9 1-161-953-00 ceramic 0.0047 µF 400 V (safety-critical); F401 1-532-612-00 time-lag 160 mA; D1 to D4 10E2; D6 RB402; IC1 SI-3052V; IC2 SI-3122V; IC3 NJM79L12A; L1 22 µH micro inductor; LED D1 SLP171D; RF modulator 1-464-384-11 (55P/75P) or 1-464-383-11 (75B); +5 V board 1-613-624-11; +12 V board 1-613-625-11. Hosted here as Sony HB-55P, HB-75P and HB-75B Service Manual.
  5. ↑ 5.0 5.1 5.2 5.3 Sony, HB-55P/75P/75B Service Manual, PDF pages 9 and 10 (printed 2-1 to 2-3): upper cabinet removal (three screws in the lower cabinet; unplug CN11 (13-pin) and CN12 (9-pin) on the main board and CN2 (2-pin) on the power board; release three hooks); main board removal (four heat sink screws, three main board screws, two screws in the blind plate, unplug CN10 (8-pin)); on the HB-75P/75B the function and cursor keytops are not locked in, so take the keyboard out and tape them before handling it; the BASIC ROM can be a single MSM38256-70RS mask ROM at IC42 with jumpers JW5 and JW7 to JW10 set to MASK and IC43 removed; the firmware ROM IC44 is an MSM38128A-77RS, with JW6 removed for an EPROM; parts marked with a warning triangle are safety-critical. Hosted here as Sony HB-55P, HB-75P and HB-75B Service Manual.
  6. ↑ MSX Cartridge slot, MSX Resource Center wiki—link(accessed 2026-10-21) Pin-out of the MSX cartridge slot: pins 41 and 43 ground, 45 and 47 +5 V, 48 +12 V, 50 −12 V, 49 sound input, 42 CPU clock 3.579545 MHz; +5 V must supply up to 300 mA per slot and ±12 V up to 50 mA for all slots.
  7. ↑ Photograph posted to msx.pics on 25 March 2019 (https://www.msx.pics/image/Ud0TS), linked from the MSX Resource Center's vulnerable hardware page: "These capacitors had exploded on the Sony HB-75P when I got it", showing two small regulator boards marked RE-19 (1-615-726-11) and RE-20 (1-615-727-11) with replacement electrolytics and film capacitors marked 330nK beside each regulator.
  8. ↑ 8.0 8.1 Vulnerable MSX hardware, MSX Resource Center wiki—link(accessed 2026-10-21) All MSX2 and later machines have a battery for the real-time clock; drained batteries, alkaline ones especially, leak; take removable batteries out before storage; lithium AA cells as an alternative. Lists the Sony HB-75P ("not as serious, as the problem caps are on separate small PCBs"), HB-F1II, HB-F1XD, HB-F1XDJ ("the ELNA caps are risky, the Nichicon ones are ok"), HB-F1XDmk2 and HB-F1XV among models with leaky capacitors. Fractured solder joints on DIN, RCA and DE-9 connectors cause flickering video and crackling sound; reflow them.
  9. ↑ 9.0 9.1 Sony, HB-55P/75P/75B Service Manual, PDF pages 62 and 63 (printed 6-1 and 6-2), alignment, in this order: VCO phase, TP1 (junction of R37 and R38) 7.0 V ±0.1 V, set with VC1; subcarrier frequency, TP2 (junction of C28 and C47) 4.433618 MHz ±10 Hz, set with VC2; video output level, TP3 (pin 2 of CN1 on the power board) 1 V ±0.1 V p-p into 75 Ω, set with VR4; on the HB-75P/75B only, RGB levels 0.7 V ±0.1 V p-p into 75 Ω at TP4 (blue, pin 3 of CN3, VR1), TP5 (red, pin 15 of CN3, VR2) and TP6 (green, pin 11 of CN3, VR3), with a white screen from COLOR 15,15. Hosted here as Sony HB-55P, HB-75P and HB-75B Service Manual.


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