Sharp Hotbit HB-8000 Service Manual

The HB-8000 service manual is Epcom's service manual for the Sharp Hotbit HB-8000 MSX computer, in Portuguese, with a cover dated November 1985. The cover names the maker as Epcom Equipamentos Eletrônicos Ltda. and says the machine was produced in the Manaus free trade zone. The copy on the wiki is a 27-page scan from MSXPRO, recompressed to 200 dpi greyscale. Several pages carry the stamp of Esbrel, with an address in Rio de Janeiro.

Contents

Section	Printed page	PDF page
Cover ("Apresentação")	1	1
Circuit description ("Descrição do circuito"): overview of the HB-8000 and a block diagram of the signal paths	3	2
Block diagram with IC numbers; 01 CPU and its pin functions	4 to 5	3 to 4
02 reset circuit, 03 wait circuit, 04 bus drivers, ROM, 06 RAM, 07 dynamic RAM interface, 08 video processor	5 to 6	4 to 5
Video processor pin functions, video RAM (CI25 and CI26), 09 sound and control processor	7	6
Pin-outs of the ICs ("Esquema - Impresso - Montagem"): HM4864, AY-3-8910, LM1889, TMS9128, 74LS series, 4013, 4016, 7445, 27256, 8255A, Z80A, TMS4416	9 to 12	7 to 10
Connector pin-outs: slots J1 and J2, printer J20, cassette J35, joysticks	13	11
Main board schematic, as one reduced sheet and in two halves	–	12 to 14
Main board component layout (one sheet marked REV-2)	–	15 to 16
RF modulator schematic and board layout (the same drawing twice)	–	17 to 18
Power supply schematic and board layout (the same drawing twice)	–	19 to 20
Exploded views	–	21 to 23
Track drawing of a board marked REV-1	19	24
Adjustments ("Ajustes"): power supply, oscillator, RF, sound, phase, video and sound check	20	25
Parts list ("Código de componentes"): main board ICs, transistors, diodes, capacitors, resistors and other parts	21	26
Parts list: RF modulator board; first lines of the power supply section	22	27

The sections a repairer will use most:

• Adjustments (printed page 20): +12 V set with VR101 at pin 3 of J15; the clock set with trimmer C12 for 3.575611 MHz at pin 37 of CI27; the RF channel 3 and 4 coils L305 and L304, the sound carrier coil L307 and the burst phase control VR301; and a BASIC program that draws 16 colour bars and plays sound.
• The power supply schematic (PDF pages 19 and 20), also hosted as File:Sharp Hotbit HB-8000 power supply circuit (service manual).png.
• The block diagram (printed page 4), also hosted as File:Sharp Hotbit HB-8000 block diagram (service manual).png.
• The parts lists (printed pages 21 and 22), with Epcom part codes and the value and voltage of each capacitor on the main and RF boards.

What this manual does not contain

• Printed pages 2 and 8 are not in the scan. The parts list stops after the three power supply ICs (741C, LM723C and 7912) at the foot of printed page 22, so the power supply's transistors, diodes, capacitors and resistors are not listed. Their values can be read from the schematic.
• There is no written disassembly procedure and no fault-finding section.
• The crystal frequency differs between sections. The circuit description gives 10.726834 MHz for the video processor's crystal, and the clock adjustment's target of 3.575611 MHz is one third of that, but the parts list gives X1 as 10.738635 MHz.
• C31 is drawn on the schematic as a 4.7 µF electrolytic at the Z80 reset pin, but listed as a 1 nF ceramic. The details are in the Sharp Hotbit HB-8000 Capacitor Replacement Guide.
• The schematic labels the main RAM chips 4164, while the parts list gives HM-4864P3.

Pages that cite this document

• Sharp Hotbit HB-8000: chips, boards, connectors and specifications.
• Sharp Hotbit HB-8000 General Maintenance: power supply, clock and RF adjustments and the video and sound check.
• Sharp Hotbit HB-8000 Troubleshooting Guide: power supply, reset, RAM, video and cassette circuits.
• Sharp Hotbit HB-8000 Capacitor Replacement Guide: electrolytic lists for all three boards.

References

Download: Sharp Hotbit HB-8000 Service Manual.pdf