Commodore Amiga
Interactive Flowchart Big-Box Amiga (A2000 / A4000)
A2000 Rev 6.2 & A4000 Rev B — Zorro II / Zorro III workstation mainboards
Complete Diagnostic Flowchart: Amiga 500/600/1200 Boot Color Code, Chip RAM & Audio/Video Isolation (Commodore Amiga 500 (Rev 3/5/6A) / A600 / A1200)
STEP 1: Check Amiga PSU Rails (+5V, +12V, -12V) & 68000 Pin 18 (/RESET)
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Measure +5V DC at MC68000 (U1) Pin 14 (VCC) and Pin 18 (/RESET) + Pin 17 (/HALT). Verify /RESET and /HALT rise cleanly from 0V to +4.8V ~500 ms after power-on.
Expected Reading: +4.85V to +5.15V DC on VCC; Pin 18 (/RESET) and Pin 17 (/HALT) steady HIGH (+4.8V).
STEP 2: Does the Screen Stop on GREEN (Chip RAM / Agnus) or Boot with Distorted Audio?
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Observe the RGB / Composite screen during boot: Dark Grey -> Light Grey -> White -> Kickstart screen. Choose YES if the screen turns GREEN (Chip RAM error) or stays Black/Dark Grey; choose NO if the system boots to Workbench/Kickstart with quiet/distorted audio or flickering video.
Expected Reading: YES = Isolate Fat Agnus (U2 PLCC-84) & Chip RAM / A501 Varta corrosion; NO = Isolate Paula audio coupling caps (C324/C334).
[ISOLATED FAULT: RES-AMIGA-RESET] Fault Isolated: 68000 Double Bus Fault (/HALT Low) or Kickstart ROM / CIA1 U7
VERDICT
The 68000 CPU is halting immediately after reset because it cannot read valid vectors from Kickstart ROM (U6) or CIA1 (U7 8520) /OVL overlay pin.
[ISOLATED FAULT: RES-AMIGA-GREEN-RAM] Fault Isolated: Green Screen — Chip RAM (U16–U19) or Fat Agnus (U2) Socket Contact
VERDICT
Kickstart's early self-test detected a failure in the lower 256KB/512KB Chip RAM or DMA address multiplexing through Fat Agnus (U2).
[ISOLATED FAULT: RES-AMIGA-AUDIO-CAPS] Fault Isolated: Leaking Audio Coupling Capacitors (C324/C334) & LF347 Op-Amp Bias
VERDICT
Tinny, quiet, or distorted left/right audio channels with a working boot screen are classic symptoms of dried-out 22µF bipolar/electrolytic audio coupling caps and -12V op-amp supply issues.
Summary
Big-Box Amigas suffer two critical threats: Varta NiCd barrel battery alkaline corrosion on both the A2000 and A4000 (near the 68000 socket / RTC chip), and severe SMD electrolytic leakage across the A4000 audio/video section and A3640 68040 CPU card.
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
A3640 CPU Card Silkscreen Polarity Trap (CE104, CE105, CE107)
On the Commodore A3640 Rev 3.0/3.1 68040 CPU board, the silkscreen polarity markings for CE104, CE105, and CE107 are REVERSED (+5V connected to the negative pad). Always connect the POSITIVE leg of the new capacitor to the +5V plane!
Cut out the Varta NiCd barrel battery immediately
Neutralise green/blue alkaline crystals around U177 (RP5C01 RTC) and U352/U350 latches with white vinegar followed by 99% IPA.
Is This Your Board?
- Amiga 2000 Rev 6.2 has 5 Zorro II slots and all through-hole axial/radial capacitors.
- Amiga 4000 Rev B uses surface-mount electrolytics across the audio/Lisa/clock sections; the A3640 68040 card has three notorious 100 uF SMD cans (CE104, CE105, CE107) printed backwards on the factory silkscreen!
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.
Amiga 4000 Rev B Mainboard
| Ref | Value | Voltage | Type | Function | Notes | Confidence |
|---|---|---|---|---|---|---|
C144 |
47 uF | 16 V | SMD | Clock buffer decoupling | Verified | |
C186 |
47 uF | 16 V | SMD | Memory controller rail | Verified | |
C303 |
22 uF | 25 V | SMD | LF347 op-amp +12V | Verified | |
C304 |
22 uF | 25 V | SMD | LF347 op-amp -12V | Verified | |
C305 |
10 uF | 25 V | SMD | Paula audio ref | Verified | |
C306 |
100 uF | 6.3 V | SMD | Paula audio filter | Verified | |
C324 |
22 uF | 25 V | SMD | Left audio coupling | Verified | |
C334 |
22 uF | 25 V | SMD | Right audio coupling | Verified | |
C407 |
10 uF | 25 V | SMD | Lisa DAC ref | Verified | |
C409 |
100 uF | 6.3 V | SMD | Video DAC decoupling | Verified | |
C811 |
470 uF | 16 V | Radial | +5V mainboard bulk | Verified | |
C812 |
470 uF | 16 V | Radial | +5V mainboard bulk | Verified |
Amiga 4000 Rev B Mainboard — shopping list
- 2 x 47 uF 16 V SMD
- 4 x 22 uF 25 V SMD
- 2 x 10 uF 25 V SMD
- 2 x 100 uF 6.3 V SMD
- 2 x 470 uF 16 V Radial
Amiga 2000 Rev 6.2 Mainboard
| Ref | Value | Voltage | Type | Function | Notes | Confidence |
|---|---|---|---|---|---|---|
C303 |
22 uF | 25 V | Radial | Audio op-amp +12V | Verified | |
C304 |
22 uF | 25 V | Radial | Audio op-amp -12V | Verified | |
C306 |
10 uF | 25 V | Radial | Audio filter | Verified | |
C307 |
470 uF | 16 V | Radial | +5V decoupling | Verified | |
C324 |
22 uF | 25 V | Radial | Left audio out | Verified | |
C334 |
22 uF | 25 V | Radial | Right audio out | Verified | |
C401 |
3300 uF | 16 V | Axial | +5V primary bulk | Verified | |
C402 |
3300 uF | 16 V | Axial | +5V secondary bulk | Verified | |
C811-C816 |
100 uF | 25 V | Radial | Zorro slot & rail decoupling (x6) | Verified |
Amiga 2000 Rev 6.2 Mainboard — shopping list
- 4 x 22 uF 25 V Radial
- 1 x 10 uF 25 V Radial
- 1 x 470 uF 16 V Radial
- 2 x 3300 uF 16 V Axial
- 1 x 100 uF 25 V Radial
Whole-Machine Shopping List
- 2 x 47 uF 16 V SMD
- 4 x 22 uF 25 V SMD
- 2 x 10 uF 25 V SMD
- 2 x 100 uF 6.3 V SMD
- 3 x 470 uF 16 V Radial
- 4 x 22 uF 25 V Radial
- 1 x 10 uF 25 V Radial
- 2 x 3300 uF 16 V Axial
- 1 x 100 uF 25 V Radial
Recap Tips
- Replace the Varta barrel battery with a CR2032 coin cell holder + Schottky blocking diode (1N5817) so the charging circuit never tries to charge the lithium cell.
Related Symptoms
- Green screen on boot (A2000/A4000) Corroded Agnus/Alice or Chip RAM address traces near the leaked RTC battery.
Sources & References
- Console5 TechWiki - Amiga 4000 A4000 Rev B and A3640 capacitor tables.