Osborne Vixen Capacitor Replacement Guide
Capacitor values for the Osborne Vixen, from Osborne's own lists of materials in the March 1983 Vixen engineering drawings.[1] These lists describe the 1983 design. Osborne's 1985 Theory of Operation Manual describes a later system board (revision C schematics) with a different ROM, disk controller and video arrangement, so check each position on your own board before ordering parts.[2]
Safety
[edit | edit source]The Vixen has a built-in CRT, which can hold a dangerous charge after the machine is unplugged. Read CRT Discharge Procedure before opening the case. The power supply runs from the mains; treat its capacitors as charged until you have measured them.
Main logic board
[edit | edit source]| Ref | Value | Type | Osborne part no. |
|---|---|---|---|
| C1, C2 | 47 µF 10 V | Low profile, aluminium | 7P45606-00 |
| C3, C4 | 68 µF 10 V | Low profile, aluminium | not given |
| C7 | 10 µF 10 V | Low profile, aluminium | not given |
C6 does not appear in the list. The other capacitors are ceramic: 0.01 µF 10 V ±30 % axial at C8 to C27 and C36 to C44 (29 parts, 7P46107-00), 0.1 µF 10 V ±50 % axial at C28 to C35 (8 parts, 7P46108-00), and 470 pF 25 V at C5 (7P46109-00).[1]
The schematic in the same package, drawing 1M00015 revision 2 (issued December 1982), does not match the list at every position. It agrees with the list that C1, the reset capacitor, is 47 µF, but marks C3 and C4 as 15 µF, across the +5 V and +12 V inputs, and C5 as 330 pF. It puts C2 across the −12 V input, with no value, and shows C6 as 10 µF beside the double-density hybrid. On that drawing a 10 V part at C2 or C4 would sit on a 12 V rail, so find which rail each position is on and choose the voltage rating from that.[3]
The revision C system board in the hosted Vixen schematic set (drawn July 1984) numbers its capacitors differently. C1 is the 330 pF oscillator capacitor and the reset capacitor is C8, marked .47 µF. C2 to C7 are polarised capacitors on the filtered supply inputs: C2 and C3 on +5 V logic, C4 on +5 V for the drives, C5 on +12 V for the drive, C6 on −12 V and C7 on +12 V logic. No values are printed for C2 to C7. The 1983 designators in the table above do not apply to this board.[4]
I/O board
[edit | edit source]| Ref | As listed | Osborne part no. |
|---|---|---|
| C1 | 22 µF 16 V aluminium | 7P45601-00 |
| C2 to C11 | "10UF, 25V, 30%, CER, AXIAL" (10 parts) | 7P46104-00 |
The I/O list prints C2 to C11 as 10 µF ceramics. Osborne's Osborne 1 list gives the same part number, 7P46104-00, to a 0.01 µF ±30 % 25 V axial ceramic, so the printed value may be a typing error. Read them on the board.[1][5]
Power supply and monitor
[edit | edit source]No parts list for the Vixen power supply or monitor is hosted here. The Vixen schematic set includes an Osborne drawing of an Astec switching supply with designators but no component values, and a Zenith monitor schematic (drawing 123-5657) with values; the 1983 drawing package names a Kaga monitor, so confirm which monitor your machine has before using the Zenith drawing.[6][1] Read values from the parts themselves before removing them.
Procedure
[edit | edit source]- Discharge the CRT and unplug the machine.
- Photograph each board and note the polarity of every electrolytic.
- Fit parts of the same capacitance and an equal or higher voltage rating that fit the low-profile footprint.
- Confirm each position on the board itself; the production board differs from the 1983 design.
See Capacitor Failure Symptoms and Recommended Tools.
Related pages
[edit | edit source]- Osborne Vixen
- Osborne Vixen Maintenance Guide
- Osborne Vixen Troubleshooting Guide
- Osborne Vixen Engineering Drawings Mar83
- Osborne 1 Capacitor Replacement Guide
- Osborne Executive Capacitor Replacement Guide
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 Osborne Computer Corporation, Vixen Engineering Drawings, March 1983, hosted at Osborne Vixen Engineering Drawings Mar83. Detached List of Materials, VIXEN MAINLOGIC, LM# 6M00015-01, revision 2.1, 13 March 1983 (PDF pages 12 to 15, items 045 to 050); Detached List of Materials, VIXEN I/O, LM# 6M00016-01, revision 1.1, 13 March 1983 (PDF pages 27 and 28, items 012 and 013).
- ↑ Osborne Computer Corporation, Osborne 4 Theory of Operation Manual, Revision 1.0, part no. 2F40006-01, August 1985, hosted as File:Osborne 4 Theory of Operation Manual Rev 1.0 1985.pdf. Sections 5.2 (ROM), 9.0 (1797 floppy disk controller) and 10.0 (display control).
- ↑ Osborne Computer Corporation, schematic, OCC4 system board, drawing 1M00015 revision 2, sheet 1 (oscillator, CPU and reset: C1, C5) and sheet 9 (disk controller and DC input: C2, C3, C4, C6), in the Vixen Engineering Drawings, hosted at Osborne Vixen Engineering Drawings Mar83 (PDF pages 16 and 24).
- ↑ Osborne Computer Corporation, Vixen system board schematic, revision C, drawn 31 July 1984, sheet 1 (oscillator and reset: C1, C8) and sheet 4 (DC input filtering: C2 to C7), in the Vixen schematic set hosted as File:Vixen Schematic.pdf (PDF pages 5 and 8).
- ↑ Osborne Computer Corporation, Osborne 1 Technical Manual, 1982, hosted at Osborne 1 Technical Manual. Detached List of Materials, Main Logic PCB Assembly, LM# 3A10063-06, item 056 (7P46104-00, CAP, AXL, CER, .01UF, ±30 %, 25 V).
- ↑ Osborne Computer Corporation, Vixen schematic set, 13 sheets, hosted as File:Vixen Schematic.pdf. Sheet 1, power supply (Astec, drawn 10 August 1983); sheet 2, Zenith monitor schematic 123-5657, issue A.