CP/M Luggables
Interactive Flowchart Osborne 1 & Kaypro II
Osborne 1 (OCC1) & Kaypro II (81-110) + Astec PSU — Z80A CP/M portable sewing-machine luggables
Complete Diagnostic Flowchart: Capacitive Load, ESR & Power Rail Ripple Diagnostic Tree (Universal Retro Mainboards (C64, Amiga, ZX Spectrum, Game Gear, Consoles))
STEP 1: Measure 100Hz/120Hz Peak-to-Peak AC Ripple on the +5V / +12V Bulk Filter Cap
[node-1]
Set your oscilloscope to AC Coupling, 200 mV/div, and 2.5 ms/div (20 MHz bandwidth limit ON). Probe directly across the main bulk filter capacitor (e.g. C19 2200µF / C88 1000µF on C64, or C303/C304 on Amiga) under full system load. Measure the peak-to-peak sawtooth ripple amplitude (mVpp).
Expected Reading: < 50 mVpp clean regulated rail (post-regulator) or < 350 mVpp on raw unregulated bulk DC before the 7805/7812.
STEP 2: Check Linear Regulator (7805 / 7812) Input-to-Output Dropout Margin
[node-2]
Switch oscilloscope or multimeter to DC Volts and measure Pin 1 (Input) of the 7805 (+5V) or 7812 (+12V) regulator at the bottom of the ripple trough. Verify that Input Voltage remains at least 2.0V above the regulated output (e.g. ≥7.2V into a 7805, ≥14.2V into a 7812).
Expected Reading: 7805 Input ≥ 7.2V DC; 7812 Input ≥ 14.2V DC. Below this dropout threshold, ripple punches straight through to the logic rail.
STEP 3: Check Local IC Decoupling & Audio/Video AC Coupling Capacitors
[node-3]
Probe audio output coupling caps (e.g. C91 100µF on C64 SID Pin 27, or C324/C334 22µF SMD on Amiga Paula) — compare upstream vs. downstream signal amplitude. Inspect SMD electrolytic pads (Amiga 600/1200, Game Gear, DMG-01) under magnification for fishy odor, dull grey solder corrosion, or lifted copper traces.
Expected Reading: Full audio/video swing across the coupling capacitor with zero DC leakage on the output side and clean, shiny solder pads.
[ISOLATED FAULT: RES-BULK-CAP] Fault Isolated: High-ESR Bulk Filter Capacitor (>100 mVpp Rail Ripple)
VERDICT
Excessive 100/120Hz sawtooth ripple on the DC rail confirms that the primary reservoir/filter electrolytics have dried out and lost effective capacitance.
[ISOLATED FAULT: RES-REG-DROPOUT] Fault Isolated: Linear Regulator Dropout / Bridge Rectifier Diode Open
VERDICT
The pre-regulator DC rail is sagging below the minimum 2V dropout headroom required by the 7805/7812 regulator.
[ISOLATED FAULT: RES-COUPLING-CAP] Fault Isolated: Open/Leaky Audio or Video Coupling Capacitor & Trace Corrosion
VERDICT
Signal attenuation, muffled audio, or DC offset hum across the coupling stage indicates dried-out or leaking coupling capacitors.
[ISOLATED FAULT: RES-RAILS-HEALTHY] Verification Passed: Power Rails, Ripple & Coupling Capacitors Within Spec
VERDICT
All measured DC supply rails, AC ripple levels (<50 mVpp), and coupling stages pass bench specification. If performing a preventive recap, use the verified board BOM below.
Summary
The Osborne 1 and Kaypro II both use Astec switched-mode power supplies fitted with two RIFA PME271M metallised paper X2 suppression capacitors (0.1 uF and 0.047 uF / 0.47 uF) that are guaranteed to split and erupt in smoke if powered on un-serviced.
Interactive Bench Oscilloscope — Verify Pre- & Post-Recap Waveforms
Open Full Signal Visualizer →Click any test point below to compare a healthy recapped rail or clock against high-ESR electrolytic capacitor ripple and droop:
Safety & Warnings
Replace the RIFA X2 mains filter capacitors before plugging in an Osborne 1 or Kaypro II!
Also remember that the Osborne 1 requires the dual-row jumpers on its front-panel 'VIDEO' connector to be plugged in for the internal 5-inch CRT to receive power and video!
Is This Your Board?
- Osborne 1 uses the Astec AC8151 open-frame PSU mounted behind the right-hand floppy drive.
- Kaypro II uses the 81-110 mainboard and an Astec or Boschert open-frame PSU at the rear.
Verified
Check
Verified rows are agreed by two or more independent sources. Check rows are revision-dependent or single-sourced — confirm the value against your own board before ordering.
Astec AC8151 Switched-Mode PSU (Osborne 1 & Kaypro II)
| Ref | Value | Voltage | Type | Function | Notes | Confidence |
|---|---|---|---|---|---|---|
C1 |
0.1 uF (100 nF) | 275 V AC | Class X2 Film | Mains live-neutral X2 filter | Mandatory RIFA PME271M replacement. | Verified |
C2 |
0.047 uF (47 nF) | 275 V AC | Class X2 Film | Mains secondary X2 filter | Mandatory RIFA PME271M replacement. | Verified |
C10 |
2200 uF | 16 V | Radial (Low-ESR) | +5V DC output reservoir | Verified | |
C11 |
1000 uF | 16 V | Radial (Low-ESR) | +5V DC secondary filter | Verified | |
C12 |
1000 uF | 25 V | Radial (Low-ESR) | +12V DC CRT & floppy motor rail | Verified | |
C14 |
100 uF | 25 V | Radial | -12V DC RS-232 bias rail | Verified |
Astec AC8151 Switched-Mode PSU (Osborne 1 & Kaypro II) — shopping list
- 1 x 0.1 uF (100 nF) 275 V AC Class X2 Film
- 1 x 0.047 uF (47 nF) 275 V AC Class X2 Film
- 1 x 2200 uF 16 V Radial (Low-ESR)
- 1 x 1000 uF 16 V Radial (Low-ESR)
- 1 x 1000 uF 25 V Radial (Low-ESR)
- 1 x 100 uF 25 V Radial
Osborne 1 / Kaypro II Z80A Mainboard
| Ref | Value | Voltage | Type | Function | Notes | Confidence |
|---|---|---|---|---|---|---|
C1 |
100 uF | 16 V | Axial / Radial | +5V logic entry decoupling | Verified | |
C2 |
47 uF | 25 V | Axial / Radial | +12V rail decoupling | Verified | |
C8 |
10 uF | 25 V | Radial | Z80A power-on /RESET delay | Verified |
Osborne 1 / Kaypro II Z80A Mainboard — shopping list
- 1 x 100 uF 16 V Axial / Radial
- 1 x 47 uF 25 V Axial / Radial
- 1 x 10 uF 25 V Radial
Whole-Machine Shopping List
- 1 x 0.1 uF (100 nF) 275 V AC Class X2 Film
- 1 x 0.047 uF (47 nF) 275 V AC Class X2 Film
- 1 x 2200 uF 16 V Radial (Low-ESR)
- 1 x 1000 uF 16 V Radial (Low-ESR)
- 1 x 1000 uF 25 V Radial (Low-ESR)
- 1 x 100 uF 25 V Radial
- 1 x 100 uF 16 V Axial / Radial
- 1 x 47 uF 25 V Axial / Radial
- 1 x 10 uF 25 V Radial
Recap Tips
- Inspect the dipped tantalum decoupling caps along the 4116 DRAM bank on early Kaypro II boards - a single shorted tantalum on the -5V or +12V rail will shut down the PSU.
Related Symptoms
- No raster on Osborne 1 5-inch CRT Check that the front-panel VIDEO shunt plug is inserted!
Sources & References
- Osborne 1 Technical Manual & Astec AC8151 Schematic Official Osborne Computer Corp schematics.