Sony HB-101 General Maintenance

Removing the HB-101P's upper cabinet and the PU-34 board (Sony service manual, page 2-1)

Routine work on the Sony HB-101 covers opening the case, removing the keyboard, checking the internal mains supply and its three output rails, and the clock adjustment in Sony's service manual. The steps and references below are from Sony's service manual for the European HB-101P and HB-201P, which share the PU-34 main board. The Japanese HB-101 has a different main board, the PU-28, which the manual does not cover; on that model use the steps as a guide only. The HB-201 guide covers the differences on that model.

Safety

Warning: the HB-101 has its mains transformer, fuse and power switch inside the case. With the cable plugged in, mains voltage is present on the FU-29 board, the power switch and the transformer primary. Unplug the mains cable before removing any screws. Sony marks these parts as critical to safety and lists exact replacements.

The HB-101P type 1 has a voltage selector for 120 V or 240 V. Check it before connecting the machine; type 2 runs on 220 V only.

Opening the case

Sony's removal procedure for the HB-101P and HB-201P:

1. Unplug the mains cable and disconnect all cartridges and cables.
2. Remove the five screws.
3. Push a flat-blade screwdriver into the slits on the right and left to release the claws.
4. Raise the front of the upper cabinet, move it in the direction of the arrow in the drawing, and release the claws at the back.
5. Pull the POWER switch out of the cabinet.
6. Lift the upper cabinet away and pull the keyboard's tape cable out of its connector.

To remove the PU-34 board:

1. Remove the two screws of the cartridge holder.
2. Remove the four screws of the upper shield plate (AE version).
3. Remove the screw of the grounding lug.
4. Disconnect CN13 and CN14, the cables from the transformer and the RE-23 regulator board.
5. Remove the three screws holding the PU-34 board and lift it out.

Removing the keyboard

1. Disconnect the LED connector.
2. Remove the six screws that hold the keyboard unit and lift it out.
3. Remove the 21 screws on the keyboard to separate it.

Cleaning

With the boards out, wash the plastic cabinet parts in warm water with a little washing-up liquid and dry them fully. Clean the cartridge slot contacts and the controller connectors with isopropyl alcohol. Sony's manual cautions against touching the controller connector pins with bare hands. Brush dust off the PU-34 board and look for leaked electrolyte around the reservoir capacitors C30 and C31 and the ±12 V parts C32, C33, C36 and C37, which the location list places in grid row A of the board drawing.

Power supply checks

The transformer's 8 V centre-tapped winding feeds D1 and D2 (S2V20) and the two 4700 µF reservoirs C30 and C31 on the PU-34 board. That unregulated supply goes out on CN14 to the RE-23 board, whose SI-3052V regulator returns +5 V to the main board. A separate 16 V winding feeds D3 and D4 (10E-2), C32 and C33, and the regulators IC48 (µPC78L12, +12 V) and IC49 (NJM79L12A, −12 V).

HB-101P and HB-201P supply rails (Sony service manual)

Rail	Regulator	Fed from	Measure across
+5 V	IC101, SI-3052V, on the RE-23 board	8 V winding, D1 and D2, C30 and C31 (4700 µF)	C903 (47 µF) on the RE-23 board
+12 V	IC48, µPC78L12	16 V winding, D3, C32 (330 µF)	C36 (47 µF)
−12 V	IC49, NJM79L12A	16 V winding, D4, C33 (330 µF)	C37 (47 µF)

Sony gives no tolerance for these rails. If +5 V is low, measure the unregulated voltage across C30 and C31 before condemning the SI-3052V. The Sony HB-101 Troubleshooting Guide goes through the faults.

The mains fuse F901 is on the FU-29 board: T400mA on the 220 V AE version and T160mA on the 120/240 V E version. Replace it only with the same rating. The transformer's thermal fuse is drawn inside the transformer.

Clock adjustment

Sony's only adjustment for this board sets the CPU clock:

1. Switch the computer on.
2. Connect a frequency counter to pin 6 (φ) of IC6, the CPU, on the PU-34 board.
3. Adjust VC1 until the counter reads 3.562500 MHz ±10 Hz.

The HB-101P's specification gives the CPU clock as 3.56250 MHz, slightly below the 3.579545 MHz of the HB-10P.

Firmware ROM jumper

The Personal Databank ROM is IC8. Sony supplies it as a mask ROM (MSM38128A-F6RS for the HB-101P, TMM23128P-8712 for the HB-201P), and the manual says to fit it at IC8 with jumper JW1 set to its MASK side. The jumper's other position is marked EP, for an EPROM.

Capacitors

The board's electrolytic capacitors are listed in the Sony HB-101 Capacitor Replacement Guide. General signs of failure are in Capacitor Failure Symptoms.

Things that are not faults

• The Personal Databank menu appears at switch-on. Hold CTRL, SHIFT, CODE and GRAPH while switching on to go straight to BASIC, then type SCREEN 0.
• The PAUSE button stops the CPU, and its lamp stays lit until it is pressed again.
• Sony's manual warns that if the power is switched on again straight after being switched off, the computer may not start correctly. Wait a moment before switching on again.

Maintenance checklist

1. On a type 1 machine, check the voltage selector.
2. Unplug the mains cable before opening the case.
3. Look for leaked electrolyte around C30 to C37 and on the RE-23 board.
4. Check +5 V across C903, +12 V across C36 and −12 V across C37.
5. Clean the cartridge slot and controller connector contacts.
6. If you have a frequency counter, check the 3.5625 MHz clock at IC6 pin 6.

Related pages

• Sony HB-101
• Sony HB-101 Troubleshooting Guide
• Sony HB-101 Capacitor Replacement Guide
• Sony HB-201 General Maintenance
• Sony HB-101P and HB-201P Service Manual
• Recommended Tools