Jump to content

Sharp Hotbit HB-8000 Capacitor Replacement Guide

From RetroTechCollection
Sharp Hotbit HB-8000 power supply circuit (service manual)
HB-8000 power supply with C112 (4700 µF), C114 and C116 (1000 µF) and the 47 µF output capacitors C113, C115 and C117 (Epcom service manual)

The Sharp Hotbit HB-8000 has electrolytic capacitors on three boards: six on the power supply board, four on the main board and eight on the RF modulator board. Epcom's service manual lists the main board and RF board parts with values and voltages.[1] The power supply section of the parts list starts at the foot of printed page 22 with its three ICs, and the page that would list its capacitors is missing from the surviving scan, so the power supply values below are read from the schematic.[1][2]

Power supply board

[edit | edit source]
HB-8000 power supply electrolytics (from the schematic)
Ref Capacitance Voltage Position in the circuit
C112 4700 µF 25 V Reservoir after the bridge D101 to D104, for +5 V
C113 47 µF 16 V +5 V output, after fuse F102
C114 1000 µF 40 V Reservoir after D107, for the LM723 and the +12 V pass transistor T104
C115 47 µF 25 V +12 V output
C116 1000 µF 40 V Reservoir after D108, input of the 7912 (−12 V)
C117 47 µF 25 V Output of the 7912 (−12 V)

[2] The other capacitors on the board are 0.1 µF, 0.047 µF and 1 nF non-electrolytic parts. C103, across the transformer primary, is rated 400 V.[2] One owner on the MSX Resource Center forum brought a dead HB-8000's power supply back by replacing all its capacitors and its coil.[3]

Main board

[edit | edit source]
HB-8000 main board electrolytics
Ref Capacitance Voltage Epcom code Position in the circuit
C1 10 µF 50 V 4.19.0000.29-2 Sound input from pin 49 of slot J1 to the audio output stage (T3)
C2 22 µF 50 V 4.19.0000.25-6 Power-on reset timing, with the reset switch SW1 and T1
C9 10 µF 50 V 4.19.0000.29-2 Cassette output to pin 4 of J35
C42 470 µF 16 V 4.19.0000.52-2 (VCEAAU1CW477M) Not shown on the schematic pages examined

[1][4] C12 is the 6.8 to 45 pF trimmer for the clock adjustment, not an electrolytic.[1]

The schematic and the parts list disagree on C31. The schematic draws it as a 4.7 µF electrolytic on the Z80 reset pin, while the parts list gives C31 as a 1 nF (1 KpF) 500 V ceramic, VCKYPU1HB102K.[4][1] Check the part fitted to the board before ordering.

RF modulator board

[edit | edit source]
HB-8000 RF modulator electrolytics
Ref Capacitance Voltage Epcom code Type code
C301 47 µF 25 V 4.19.0000.44-3 VCEAAA1CW476M
C303 47 µF 25 V 4.19.0000.44-3 VCEAAA1CW476M
C305 1 µF 63 V 4.19.0000.47-0 VCEAAA1HW105M
C311 1 µF 63 V 4.19.0000.47-0 VCEAAA1HW105M
C323 100 µF 16 V 4.19.0000.45-2 VCEAAA1CW107M
C325 220 µF 10 V 4.19.0000.24-7 –
C326 22 µF 25 V 4.19.0000.50-4 VCEAAA1CW226M
C329 4.7 µF 63 V 4.19.0000.31-8 –

[1] The list has no C324.[1] The same forum owner repaired his machine's modulator by replacing all its capacitors.[3]

Replacement procedure

[edit | edit source]

Warning: the HB-8000 has its mains transformer, switch and fuse inside the case. Unplug the mains cable before opening it.

  1. Check the voltage selector under the case, then unplug the machine and open it. The exploded views are on PDF pages 21 to 23 of the service manual.[5]
  2. Photograph each board and note the polarity of every electrolytic.
  3. Start with the power supply: C112, C114 and C116, then C113, C115 and C117.
  4. Replace the RF modulator board's eight electrolytics, then C1, C2, C9 and C42 on the main board.
  5. Fit parts of the same capacitance and at least the same voltage.
  6. Keep the heat on each joint short. A member of the MSX Resource Center forum warns that the main board's traces and vias are fragile.[3]
  7. Before reconnecting the main board, check +5 V, +12 V and −12 V on the supply's output wires, and set +12 V with VR101 at pin 3 of J15 if needed.[6] After work on the RF board, check the RF adjustments described in General Maintenance.
[edit | edit source]

References

[edit | edit source]
  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Epcom, HB-8000 service manual (File:Sharp Hotbit HB-8000 Service Manual.pdf), parts lists ("código de componentes"): main board, printed page 21 (PDF page 26); RF modulator board, printed page 22 (PDF page 27). The lists write µF as "mF" and mark electrolytics "E" and ceramics "C". Hosted with a description at Sharp Hotbit HB-8000 Service Manual.
  2. ↑ 2.0 2.1 2.2 Epcom, HB-8000 service manual (File:Sharp Hotbit HB-8000 Service Manual.pdf), power supply schematic and layout, PDF pages 19 and 20; also File:Sharp Hotbit HB-8000 power supply circuit (service manual).png: C112 4700 µF 25 V after the bridge D101 to D104; C113 47 µF 16 V on the +5 V output after F102; C114 1000 µF 40 V after D107, feeding the LM723 and T104; C115 47 µF 25 V on the +12 V output; C116 1000 µF 40 V after D108, at the input of the 7912; C117 47 µF 25 V at the 7912 output; C103 0.1 µF 400 V across the transformer primary; C104, C106, C107, C108, C110 and C111 0.1 µF, C105 0.047 µF and C109 1 nF.
  3. ↑ 3.0 3.1 3.2 Repair of a Sharp HB-8000 Brazilian MSX computer, MSX Resource Center forum, November 2017—link(accessed 2026-10-21) Argon: power supply repaired by recapping all capacitors and replacing the coil; modulator repaired by fully recapping it. tvalenca: the main board's traces and vias are fragile and cannot take extra heat.
  4. ↑ 4.0 4.1 Epcom, HB-8000 service manual (File:Sharp Hotbit HB-8000 Service Manual.pdf), main board schematic, PDF pages 12 to 14: C1 10 µF between the SOUND IN line (pin 49 of J1) and the audio stage T3; C2 22 µF in the reset circuit with SW1, R13, D1 and T1; C9 10 µF to CMT OUT on J35; C31 drawn as an electrolytic marked 4.7 µF at the Z80 reset pin with R43.
  5. ↑ Epcom, HB-8000 service manual (File:Sharp Hotbit HB-8000 Service Manual.pdf), exploded views, PDF pages 21 to 23.
  6. ↑ Epcom, HB-8000 service manual (File:Sharp Hotbit HB-8000 Service Manual.pdf), adjustments, printed page 20 (PDF page 25): VR101 for +12 V at pin 3 of J15; C12 for 3.575611 MHz at pin 37 of CI27; RF adjustments L304, L305, L307 and VR301.



Retrieved from "https://retrotechwiki.com/index.php?title=Sharp_Hotbit_HB-8000_Capacitor_Replacement_Guide&oldid=28438"