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Sony HB-101 Troubleshooting Guide

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Sony HB-101P HB-201P power supply circuit (service manual)
HB-101P and HB-201P power supply: FU-29 fuse and switch board, transformer T901, rectifiers and reservoirs on the PU-34 board, the RE-23 5 V regulator board and the ±12 V regulators (Sony service manual, page 5-23)

Fault-finding on the Sony HB-101 starts with the internal mains supply and its three rails, then the video and memory chips. Component references are from Sony's service manual for the European HB-101P and HB-201P.[1] The Japanese HB-101 is built on a different board, the PU-28, so its reference numbers do not match these.[2]

Warning: mains voltage is present inside the case on the FU-29 board, the power switch and the transformer. Unplug the mains cable before opening the machine.

Quick reference

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Symptoms, causes and actions
Symptom Probable cause Action
Dead, power indicator dark Mains fuse F901, voltage selector (type 1), power switch S901, transformer thermal fuse See No power
Indicator lit, no picture +5 V missing or low, video chip IC14, video RAM, PAL encoder, RF modulator Check +5 V, then No picture
Machine stops responding, lamp on the PAUSE button lit PAUSE pressed Press PAUSE again
Personal Databank appears instead of BASIC Normal behaviour Hold CTRL, SHIFT, CODE and GRAPH at switch-on
Will not start properly just after being switched off Power switched back on too quickly Wait a moment and switch on again
Sound cartridges or disk interface dead, BASIC fine +12 V or −12 V missing See Missing ±12 V

[3][4][5]

No power

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  1. Unplug the machine. On an HB-101P type 1, check that the voltage selector matches the mains.[4]
  2. Open the case (General Maintenance) and check F901 on the FU-29 board. The AE version uses T400mA and the E version T160mA.[3]
  3. With F901 intact, check continuity through the power switch S901 and the transformer primary from the mains plug. The transformer has a thermal fuse in series with its primary, drawn inside the transformer.[3]
  4. Plug in and switch on. Measure across C30 or C31, the 4700 µF reservoirs on the PU-34 board. No voltage here with the primary good points to the secondary wiring at CN13 or to D1 and D2.
  5. If C30 has voltage but +5 V is missing at C903 on the RE-23 board, check the cable at CN14 and the SI-3052V regulator, IC101. Disconnect the RE-23 output and check the main board's +5 V line for a short to ground with the power off.

Before fitting a new F901, check the rectifiers D1 to D4 and the reservoir capacitors C30 to C33 for a short.

No picture

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The HB-101P's video chip is IC14, a TMS9129NL, which drives a separate PAL encoder module and the RF modulator.[6][7]

  1. Check +5 V at pin 33 of IC14 (ground pin 12).
  2. Try both the RF output and the composite video on the 6-pin DIN socket. A picture on one but not the other places the fault in the encoder or modulator.
  3. Check the CPU clock at pin 6 of IC6. Sony sets it with VC1 to 3.562500 MHz ±10 Hz.[8]
  4. Check the supply pins of the RAM chips (pin 9 +5 V, pin 18 ground).

A Japanese HB-101 described on the MSX Resource Center forum in 2025 showed garbled characters and sprites, then a dark screen with noise after it had been left running overnight. Moving the loose board changed the picture between white and noisy black. Wierzbowsky advised checking the supply voltage at every RAM chip, saying that a black screen most often means bad RAM. The thread records no fix.[9] On a board that changes behaviour when flexed, look for cracked solder joints and broken tracks before replacing chips.

Personal Databank and software

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The Personal Databank ROM takes slot 3. The MSX Resource Center notes that it has to be removed before some software, such as the Nextor disk system, will work. Unlike on the Sony HB-55, fitting a disk drive does not disable the Databank, and an HBI-55 data cartridge no longer disables the disk drive.[5] To reach BASIC, hold CTRL, SHIFT, CODE and GRAPH at switch-on and type SCREEN 0; CALL HITBIT goes back to the Databank.[10]

The firmware ROM, IC8, is a mask ROM selected by jumper JW1 on its MASK side. The other position, EP, is for an EPROM.[11] If IC8 has been replaced with an EPROM and the Databank does not start, check JW1.

Missing ±12 V

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The 16 V winding of the transformer feeds D3 and C32 for +12 V and D4 and C33 for −12 V. The regulators are IC48 (µPC78L12) and IC49 (NJM79L12A), with C36 and C37 on their outputs.[3]

  1. Measure across C32 and C33. No voltage on either points to the 16 V winding or its connection at CN13.
  2. With input voltage present, measure across C36 (+12 V) and C37 (−12 V).
  3. On IC49 the input is pin 2 and the output pin 3, with ground on pin 1.[6]

Test points

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Supply pins on the PU-34 board (Sony service manual, page 5-16)
IC Type +5 V pin Ground pin
IC6 LH0080A or µPD780C-1 CPU 11 29
IC8 Personal Databank ROM 28 14
IC9 MSM38256-78RS MSX-BASIC ROM 28 14
IC14 TMS9129NL video chip 33 12
IC20 to IC23, IC46, IC47 TMS4416-15NL dynamic RAM (µPD41254C-15 at IC22 and IC23 on the HB-201P) 9 18
IC26 YM-2149 PSG 40 1
IC30 µPD8255AC-5 PPI 26 7

[6]

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References

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  1. ↑ Sony, HB-101P/201P Service Manual (File:Sony HB-101P HB-201P Service Manual.pdf). Hosted with a description at Sony HB-101P and HB-201P Service Manual.
  2. ↑ File:Sony HB-101 (Japanese) main board.jpg, photograph uploaded to the MSX Resource Center wiki by Gdx on 16 November 2015: board marked PU-28 and 1-614-830-12, with 100-series reference numbers.
  3. ↑ 3.0 3.1 3.2 3.3 Sony, HB-101P/201P service manual (File:Sony HB-101P HB-201P Service Manual.pdf), power supply schematic on page 5-23: CN901, F901 (T400mA AE, T160mA E), S901, C901, T901 and its thermal fuse, S902 voltage change switch (E version); CN13 (AC 8 V, AC 8 V, GND, AC 16 V, GND) and CN14 (+5 V IN, DC OUT, GND) on the PU-34 board; D1 and D2 (S2V20) to C30 and C31 (4700 µF 16 V); RE-23 board with IC101 (SI-3052V), C902 (0.33 µF) and C903 (47 µF); D3 (10E-2), C32 (330 µF 35 V), C34 and IC48 (µPC78L12) for +12 V with C36 (47 µF 16 V); D4, C33, C35 and IC49 (NJM79L12A) for −12 V with C37.
  4. ↑ 4.0 4.1 Sony, HB-101P/201P service manual (File:Sony HB-101P HB-201P Service Manual.pdf), page 1-3, location and function of parts and controls: power switch and indicator, caution to wait a moment before switching on again, reset button, pause button and its lamp, voltage selector.
  5. ↑ 5.0 5.1 Sony HB-101, MSX Resource Center wiki—link(accessed 2026-10-21) Personal Databank and how to skip it; the PAUSE button halts the CPU; the firmware has to be removed to use some other software such as Nextor.
  6. ↑ 6.0 6.1 6.2 Sony, HB-101P/201P service manual (File:Sony HB-101P HB-201P Service Manual.pdf), IC supply table on page 5-16: IC6 LH0080A or µPD780C-1 (+5 V pin 11, ground 29); IC8 and IC9 ROMs (+5 V pin 28, ground 14); IC14 TMS9129NL (+5 V pin 33, ground 12); IC20 to IC23, IC46 and IC47 TMS4416-15NL or µPD41254C-15 (+5 V pin 9, ground 18); IC26 YM-2149 (+5 V pin 40, ground 1); IC30 µPD8255AC-5 (+5 V pin 26, ground 7); IC31 µPC311C (+5 V pin 8, ground 1); IC48 µPC78L12 (+12 V pin 2, ground 3); IC49 NJM79L12A (ground 1, −12 V pin 3).
  7. ↑ Sony, HB-101P/201P service manual (File:Sony HB-101P HB-201P Service Manual.pdf), electrical parts list on page 7-7: PAL encoder 1-464-507-11 and RF modulators 1-464-384-11 (HB-101P E) and 1-464-490-11 MDG-UE3602 (HB-101P and HB-201P AE).
  8. ↑ Sony, HB-101P/201P service manual (File:Sony HB-101P HB-201P Service Manual.pdf), alignment, page 6-1: counter on pin 6 (φ) of IC6, adjust VC1 for 3.562500 MHz ±10 Hz.
  9. ↑ Sony HB-101 Video Issues / Black Screen, MSX Resource Center forum, 9 May 2025 to 5 May 2026—link(accessed 2026-10-21) ScrewyClassic: Japanese HB-101 with garbled video, then a faint black screen with noise; white screen in some positions of the loose board; TMS9118NL warm; reflow made no difference. Wierzbowsky: in most cases a black screen means bad RAM; check all voltages on the RAM chips. No resolution recorded.
  10. ↑ Sony HB-101, MSX Resource Center wiki—link(accessed 2026-10-21) Personal Databank options; CTRL-SHIFT-CODE-GRAPH at boot; CALL HITBIT.
  11. ↑ Sony, HB-101P/201P service manual (File:Sony HB-101P HB-201P Service Manual.pdf), section 2-2, page 2-2: firmware ROM IC8 (MSM38128A-F6RS HB-101P, TMM23128P-8712 HB-201P), jumper JW1 MASK/EP set to MASK.


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