Big-Box Amiga Machine Hub
Amiga 1000, 2000, 3000 & 4000 workstation repair reference — VARTA battery corrosion & A3000/A4000 SMD recapping, Zorro II/III & Video Slot pinouts, PSU TICK signal & ATX conversion, and Super Buster / Ramsey / Amber diagnostics.
VARTA Barrel Battery Corrosion & A3000 / A4000 SMD Capacitor Leakage Red Alert
Every un-serviced Amiga 2000, Amiga 3000, and Amiga 4000 contains a soldered 3.6 V VARTA NiCd rechargeable barrel battery (BT100 / BT176) that ruptures and wicks corrosive potassium hydroxide (KOH) alkaline electrolyte along the copper tracks: on the A2000 it eats the 68000 CPU socket (U100) and Kickstart ROM socket (U500); on the A3000 it destroys the Amber flicker-fixer and Denise area; and on the A4000 it dissolves the thin SIMM RAM address multiplexers (U891 74FCT244) and Paula audio circuits! On top of that, the Amiga 4000 (and 3640 CPU card!) is covered in leaking SMD electrolytic capacitors that must be replaced immediately.
1 VARTA Neutralisation & Trace Checklist
- Snip the VARTA Battery Out Today: Cut the two/three legs with flush side-cutters — never rock the barrel back and forth or you will rip corroded pads off the PCB! (All Big-Box Amigas run 100% fine with no RTC battery installed!).
- Neutralise Alkaline KOH with Mild Acid: Scrub the green/blue crusted area using a stiff brush dipped in distilled white vinegar (5% acetic acid) or 10% citric acid solution until fizzing stops completely.
- Flush & Inspect Vias: Rinse thoroughly with deionised water followed by 99% Isopropyl Alcohol. Strip any blackened solder mask with a fibreglass pencil, tin bare copper, and buzz out every continuity line:
- A2000: Buzz out all 64 pins of the 68000 CPU (
U100) to the 86-pin CPU Slot (CN600) and Kickstart ROM (U500) (replace the corroded CPU socket!). - A4000: Buzz out the 32-bit Chip/Fast SIMM address/data lines through
U891,U892,U177(74FCT16244/74F245) and theRP5C01RTC chip!
- A2000: Buzz out all 64 pins of the 68000 CPU (
- CR2032 Coin-Cell + Blocking Diode Replacement: When fitting a non-rechargeable CR2032 holder, you MUST wire a
1N4148orBAT85Schottky diode in series (cathode stripe toward the RTC chip!) so the motherboard's charging resistor cannot pump current into the lithium coin cell!
2 Amiga 4000 & A3640 SMD Capacitor List
The Amiga 4000D (Rev B) mainboard and its A3640 (68040) CPU card use leaking SMD aluminium electrolytic cans. Replace with Panasonic / Wurth Polymer SMD caps:
| Board / Location | Value & Voltage | Qty | Critical Notes |
|---|---|---|---|
| A4000D Mainboard (Audio & Op-Amp) | 22 μF 25 V / 35 V(C409, C410 = BIPOLAR!) | 5× (2 Bipolar + 3 Polar) | C409 & C410 near the audio jacks are NON-POLARISED (Bipolar) 22 μF caps! |
| A4000D Mainboard (Video / Decoupling) | 47 μF 16 V | 8× | Surrounding Lisa, Alice, and DAC video output |
| A4000D Mainboard (Power / Logic) | 10 μF 25 V & 100 μF 6.3 V | 4× | Check for corroded pads under the audio op-amp (U400 LM833/TL074)! |
| A3640 (68040 Card) ( C102–C107) | 100 μF 16 V (5×) + 22 μF | 5×–6× | DANGER: Factory Silkscreen Polarity Error on A3640 Rev 3.0/3.1! See warning below! |
CRITICAL A3640 CPU CARD REVERSE-POLARITY WARNING: On Commodore's A3640 68040 CPU card, the factory silkscreen + markings for the three SMD caps C105, C106, and C107 were printed BACKWARDS (and Commodore actually soldered those three caps in backwards at the factory, causing them to leak/explode)! Always verify with a multimeter which pad connects to the GND plane and connect the POSITIVE (+) leg of C105, C106, and C107 to the +5 V pad (opposite the factory + silkscreen)!
3 Amiga 3000 Through-Hole & Daughterboard Notes
- Good news for Amiga 3000D owners: the A3000 desktop motherboard uses through-hole radial electrolytic capacitors rather than leaking SMD cans!
- However, the A3000's VARTA barrel battery sits right beside the
Amberdeinterlacer (U250),Denise(U201), and the 31.25 kHz VGA trimmer pot — battery damage here causes shimmering or dead 31 kHz VGA output! - Also check the 4-pin power Molex and Zorro riser daughterboard edge connector for heat-darkened +5 V pins.
Big-Box Model Selector & Architecture
Select your Big-Box Amiga (A1000, A2000, A3000, or A4000) to view board revisions, custom chipsets, and memory expansion architectures.
Amiga 1000 1985–1987 • Jay Miner & Team Signatures Inside Case!
The original 1985 "Lorraine" Amiga features an elevated monitor stand with an under-slung garage for the mechanical Mitsumi keyboard, an 86-pin side expansion edge connector, and a unique 256 KB Writable Control Store (WCS) daughterboard! Instead of having Kickstart in mask ROM, an un-modified A1000 boots from a tiny 8 KB bootstrap ROM ($F80000) that prompts you to insert a Kickstart 1.1/1.2/1.3 floppy disk, loads the 256 KB Kickstart image into the WCS daughterboard RAM ($FC0000–$FFFFFF), and write-protects the WCS until the next cold power-off!
Key ICs & Architecture
- CPU: Motorola MC68000P8 @ 7.16 MHz (NTSC) / 7.09 MHz (PAL)
- Agnus (48-Pin DIP!): MOS 8361 (NTSC) or 8367 (PAL) — thin 48-pin DIP Agnus addressing 512 KB max Chip RAM (
256KBon mainboard +256KBfront cartoon-box RAM module) - Denise: MOS 8362R5 / R6 (OCS, no EHB Halfbrite on very early US 8362R5!)
- Paula: MOS 8364R4 (4-ch 8-bit DMA audio, floppy & serial/pot controller)
- CIAs: 2× MOS 8520A (DIP-40)
- WCS Piggyback Daughterboard (NTSC vs Late PAL): Early NTSC A1000s carry the 256 KB WCS RAM on a vertical piggyback daughterboard (
PN 327213); late European PAL A1000s integrate the WCS RAM onto the mainboard without a daughterboard!
Amiga 1000 Quirks & Kickstart ROM Conversion
| Quirk / Upgrade | Important Bench Details |
|---|---|
Reversed External Floppy DB23 Power Pins? No — PARALLEL PORT (DB25) Gender & Pinout Trap! |
WARNING: On the Amiga 1000 ONLY, the rear Parallel Port is a DB25 MALE (same gender as standard Amiga Serial!) AND carries +5 V on Pin 23 and −5 V / +12 V on Pins 14/25! Never plug a standard PC printer or A500 parallel cable into an A1000 without an A1000 parallel adapter! |
| RJ11 / RJ9 Coiled Keyboard Cable | Uses a 4-pin handset-style modular jack (+5V, KBCLK, KBDATA, GND). Never plug an RJ11 modem/telephone line into the keyboard port! |
| ROM Adapter (Kickstart 1.3 / 3.1 in ROM) | Using a Kickstart ROM switcher adapter in the two 28-pin bootstrap ROM sockets (U5N/U5P) with two jumpers lifted on the WCS board allows an A1000 to boot Kickstart 1.3 / 3.1 instantly without a Kickstart floppy! |
Amiga 2000 / 2000HD / 2500 1987–1991 • 5× Zorro II + CPU Slot + Video Slot + ISA
The indestructible workhorse of the Amiga range. The German-designed Rev 4.x ("A2000-A") was essentially an A1000 with Zorro slots and a separate Chip RAM card in the CPU slot, quickly replaced by Dave Haynie and Terry Fisher's West Chester Rev 4.1–4.5 and Rev 6.0–6.5 ("A2000-B") motherboard featuring 5× 100-pin Zorro II AutoConfig slots, an 86-pin Coprocessor/CPU Slot, an inline Video Slot (home of the NewTek Video Toaster!), and 4× PC XT/AT ISA slots (for Bridgeboard PC cards).
Key ICs & Board Revisions (B2000-CR)
- Rev 4.1 – 4.5: 8371 (512 KB PAL) or 8370 (NTSC) PLCC-84 Fat Agnus + 512 KB Expansion RAM on motherboard (
1MBtotal:512KB Chip + 512KB Slow RAM). - Rev 6.0 / 6.2 (Most Common): Upgraded to 8372A (
1MB ECS Agnus) configuring all 1 MB (8×414256256K×4 DIP-20) on the motherboard as unified 1 MB Chip RAM! - Rev 6.3 / 6.4 / 6.5: Factory fitted with ECS Super Denise (
8373),8375(2MB-capable Agnus pinout, wired for 1MB), and Kickstart 2.04. - Buster (
U600): MOS 5721 (PLCC-68 or DIP-48) — Zorro II bus arbiter managing DMA and bus mastery across the five 100-pin Zorro II slots. - Gary (
U102): MOS 5719 (DIP-48) — System address decoder and floppy control glue.
Amiga 2000 Bench & Upgrade Checklist
| Area | Symptom & Fix |
|---|---|
VARTA Battery (BT100) Damage Zone |
Positioned immediately behind the 68000 CPU (U100) and 86-pin CPU Accelerator Slot (CN600)! Alkaline creep turns the CPU socket pins green, eating the address traces between U100, U500 (Kickstart), and CN600. Always desolder and replace the 64-pin CPU socket if any green crust is visible! |
J300 (TICK Clock Source Jumper) |
Located near the power connector! Bridges Pins 1–2 to use the 50/60 Hz TICK clock from the A2000 PSU (Pin 14), or Pins 2–3 to use internal Vertical Sync (VSYNC) when using an ATX PSU adapter that lacks a TICK generator! |
2MB Chip RAM Upgrades (MegAChip / ACE2b) |
Plugs into the 84-pin PLCC Agnus socket (plus a Gary tap), upgrading any Rev 4.x or Rev 6.x A2000 to a full 2 MB of ECS Chip RAM! |
Amiga 3000 / 3000T 1990–1992 • 32-Bit 68030 • Zorro III • Built-in Amber Deinterlacer
Often considered Commodore's finest engineering achievement. Designed by Dave Haynie, Hedley Davis, and Greg Berlin, the Amiga 3000 introduced a full 32-bit Motorola 68030 + 68881/68882 FPU (at 16 MHz or 25 MHz), 32-bit Zorro III expansion slots on a vertical riser, onboard DMA SCSI-2 (WD33C93A + Super DMAC), and the built-in Amber (390538) scan-doubler / flicker-fixer outputting crystal-clear 31.5 kHz VGA on a rear 15-pin D-Sub alongside the 15 kHz DB23 RGB port!
Custom 32-Bit Workstation Chipset
- CPU & FPU: Motorola MC68030 + MC68881 (16 MHz) or MC68882 (25 MHz) + 200-pin 32-bit CPU Fast Slot (
CN606) - Fat Gary (
390540): 32-bit system address decoder and bus controller - Ramsey (
390541-04 / -07): 32-bit Fast RAM controller supporting Static Column / Page Mode ZIP DRAMs (up to 16 MB on the motherboard!) - Super Buster (
390537/390539Rev 7, 9, or 11): Zorro III 32-bit bus arbiter (Always upgrade socketed Rev 7/9 toRev 11for Zorro III DMA stability!) - Super DMAC (
390537-02 / -04) + WD33C93A (00-08/16-08Proto): 32-bit DMA controller + SCSI host adapter - Amber (
390538) + 3× OKI MSM514221 Video Field Memories: Captures and deinterlaces 15 kHz Amiga video (including 480i/576i interlaced screens!) into rock-steady 31 kHz VGA
Amiga 3000 ZIP RAM, SuperKickstart & SCSI Quirk Guide
| Subsystem | Crucial A3000 Bench Knowledge |
|---|---|
Fast RAM ZIP Sockets (1MB×4 20-Pin ZIPs) |
The A3000 motherboard holds 32 ZIP sockets for up to 16 MB of 32-bit Fast RAM (1M×4 Page Mode 441000 or Static Column 441002 ZIPs). Because ZIP chip legs bend easily and cost a fortune today, plug in a ZIP-to-SIMM72 adapter board (or place 64–256 MB on a CPU-slot/Zorro III card!). |
| 1.4 "SuperKickstart" vs Physical 2.04/3.1/3.2 ROMs | Early A3000s shipped with Kickstart 1.4 (36.16) in ROM, which loads a .kickstart file from the hard drive into MMU-protected Fast RAM ($07F80000). Upgrading the two 40-pin ROM sockets (U180/U181 depending on J180/J181 tower/ROM timing jumpers!) to physical Kickstart 3.1.4 / 3.2.2 EPROMs boots instantly! |
WD33C93A SCSI " AMD Bug " (00-04 vs 00-08) |
Early AMD-manufactured AM33C93A SCSI chips hang on certain synchronous SCSI transfers and modern ZuluSCSI/BlueSCSI setups. Upgrade the 40-pin DIP socket (U208) to a Western Digital WD33C93A-PL 00-08 (or 14MHz clock mod)! |
Amiga 4000 / 4000CR / 4000T 1992–1996 • 68040 / 68EC030 • AGA 24-Bit Chipset • 72-Pin SIMMs
Commodore's flagship AGA (Advanced Graphics Architecture) workstation. Combines the 24-bit Lisa / Alice AGA chipset (256 simultaneous colours from a 16.8-million palette + 31 kHz DblPAL/Multiscan modes) with 72-pin SIMM sockets (for 2 MB Chip RAM + up to 16 MB motherboard Fast RAM), built-in 40-pin 3.5″ Buffered IDE, a 200-pin CPU card slot (holding the A3640 68040, A3630, or CyberStorm / BFG9060 68060), and 4× Zorro III slots + inline Video Slot on a horizontal riser card.
Key ICs & Board Revisions (A4000-B vs A4000-CR)
- Alice (
391010PLCC-84): AGA 2 MB Chip RAM DMA controller - Lisa (
391227QFP-84): AGA 24-bit video sprite & bitplane generator - Paula (
8364PLCC-52): Audio, floppy & UART controller - Fat Gary (
390540) & Ramsey (390541-07): 32-bit bus & SIMM Fast RAM controllers - Super Buster (
390539-11Rev 11): Zorro III arbiter (soldered QFP on Rev B; socketed PLCC-84 on some boards) - Bridgette (
391380QFP-100): Integrated bus buffer replacing eleven discrete 74F245 transceiver chips on the A3000! - A4000D Rev B (Most Common): Uses plug-in CPU card (
A3640/A3630), 5× 72-pin SIMMs (1× Chip + 4× Fast), and VARTA barrel battery (BT176). - A4000CR (Cost-Reduced Rev D): Soldered 25 MHz
68EC030+ soldered 2 MB Chip RAM right on the mainboard, and factory lithium coin cell instead of VARTA barrel!
Amiga 4000 Critical Jumper & SIMM Guide
| Jumper / Socket | Setting & Hardware Notes |
|---|---|
| J100 & J104 (CPU Clock Source: INT vs EXT!) | MOST IMPORTANT JUMPERS ON THE A4000! • For an A3630 (68030) card (which has no oscillator on the card): set J100 & J104 to INT (Pins 1–2).• For an A3640 (68040), A3660, or BFG9060 (68060) card (which has its own crystal oscillator): you MUST set J100 & J104 to EXT (Pins 2–3) — otherwise the A4000 stays on a completely black screen! |
J213 (2MB vs 8MB Chip RAM Size) |
Always keep J213 set to 2M (Pins 1–2)! (8M was reserved for the unreleased AAA chipset — even if you plug a 4 MB or 8 MB 72-pin SIMM into the white Chip RAM socket, J213 must stay on 2M!). |
| J852 (4MB vs 16MB Fast RAM SIMM Size) | Set to 4M (Pins 1–2) when using 1 MB/2 MB SIMMs, or 16M (Pins 2–3) when populating up to 4× 4 MB 72-pin FPM SIMMs (60ns–80ns) for 16 MB Motherboard Fast RAM! |
Boot Screen Error Colour Matrix & Custom Silicon Diagnostics
Decoding Kickstart power-on self-test screen colours and isolating faults across Agnus/Alice, Denise/Lisa, Paula, Gary, Ramsey, and Super Buster.
Amiga Kickstart Boot Screen Colour Decoder
During cold boot, the 680x0 CPU steps through a hardware verification sequence (Dark Grey → Light Grey → White → Kickstart screen), changing the background register (COLOR00 at $DFF180) immediately if a subsystem fails:
The 16-bit/32-bit Kickstart ROM checksum failed. Check for bent pins or reversed HI/LO chips in the ROM sockets (U180/U181 on A3000; U175/U176 on A4000), or corroded battery tracks between the 68000 CPU and ROM on an A2000!
Failed to read/write the base Chip RAM ($000000–$03FFFF). On A2000/A3000: reseat the 84-pin PLCC Fat Agnus socket with a proper PLCC extractor tool! On A4000: check the white Chip RAM 72-pin SIMM socket (U212) and VARTA-corroded buffer U891 (74FCT16244)!
The 680x0 hit an unexpected Bus Error, Address Error, or Illegal Instruction before software exception handlers were set up. Common causes: faulty Zorro II/III expansion card, unseated A3640 CPU card, bad Fast RAM SIMM/ZIP, or a dirty Super Buster / Ramsey socket!
Custom chip register read/write test failed. Check that +5 V and clocks are reaching Denise/Lisa, Paula, and Agnus/Alice, and check Bridgette (U205) on the A4000.
8520) or Rev 0.4 DiagROM
Failed 8520 Complex Interface Adapter timer or interrupt check (CIA-A handles keyboard/mouse button/parallel; CIA-B handles floppy step/serial/HSYNC timers).
Dark Grey: Initial CPU hardware check started but froze (check CPU card, J100/J104 INT/EXT jumpers on A4000, or missing /OVL overlay line from CIA-A Pin 2!). White Screen (30s): Normal delay if no hard drive or floppy is connected to an A3000/A4000 IDE/SCSI header!
"Black Screen / No Boot" Big-Box Decision Tree
Power supply fan spins, but monitor shows no sync or stays black without even reaching Dark Grey.
- 1. Strip All Zorro Cards, Riser & Drives First: Unplug the Zorro II/III riser daughterboard (on A3000/A4000), remove all Zorro cards, and unplug IDE/SCSI cables. A single shorted Zorro card or hung
/BERR//DTACKline on the riser will hold the entire system black! - 2. Check Power LED Brightness Change (
Dim→Bright):- At power-on, the Power LED starts dim (or off) and switches to full brightness as soon as the CPU executes the first instructions in Kickstart ROM (toggling CIA-A
PA0/LEDand releasingPA1/OVLROM overlay!). - If the Power LED never changes brightness (and pressing CAPS LOCK 15 times makes its green LED freeze on/off after ~10 presses), the CPU is not executing Kickstart ROM at all!
- At power-on, the Power LED starts dim (or off) and switches to full brightness as soon as the CPU executes the first instructions in Kickstart ROM (toggling CIA-A
- 3. Check A4000 Jumpers
J100&J104+ SIMM SocketU891: ConfirmJ100/J104match your CPU card (INTfor A3630,EXTfor A3640/060), reseat the 200-pin Kel/Molex CPU connector, and install DiagROM in the Kickstart sockets (U175/U176) while monitoring the DB25 Serial port at 9600 baud!
Super Buster, Ramsey & Amber Fault Symptoms
Diagnosing Big-Box exclusive VLSI chips on the A3000 and A4000.
- Super Buster (
390539):- Rev 7: Supports Zorro III memory cards, but locks up immediately if any Zorro III DMA bus-master card (like an A4091 SCSI-2 or Deneb USB) is installed!
- Rev 9: Supports a single Zorro III DMA master, but has bugs with multiple cards.
- Rev 11 (
390539-11): Final bug-fixed revision. Essential upgrade for any A3000/A4000 using Zorro III cards!
- Ramsey (
390541-04vs-07) & Super DMAC (-02vs-04): On the A3000,Ramsey-04must be paired withSuper DMAC-02(orRamsey-07withSuper DMAC-04); mixingRamsey-07with an earlyDMAC-02at 25 MHz causes SCSI DMA corruption unless a clock delay fix is applied! - Amber (
390538) Flicker-Fixer (A3000 / A2320): If 15 kHz DB23 RGB works fine, but the 31 kHz VGA DB15 output has vertical jailbars or rolling lines, adjust the fine-tuning capacitor/pot next to Amber (with a plastic tool while displaying a high-res interlaced screen) and check the three OKIMSM514221field memory chips!
Power Supply Pinouts (TICK Signal & ATX Conversion) & DB23 RGB
Why A2000/A3000 PSUs include a 50/60 Hz TICK square wave, how to wire an ATX PSU adapter for the A4000, and DB23 RGB + A3000 VGA pinouts.
A2000, A3000 & A4000 Motherboard Power Headers 50/60Hz TICK Signal Note!
Unlike standard PC ATX supplies, original Amiga 2000 and Amiga 3000 power supplies generate a dedicated 5 V TTL 50/60 Hz square-wave TICK clock (derived from the AC mains frequency) to drive CIA-A's Time-of-Day (TOD) counter!
A2000 14-Pin Rectangular (CN400) |
A3000 15-Pin Header (CN405) |
A4000D 6-Pin Inline Molex (CN450) |
|---|---|---|
Pins 1–4: +5V DC (Red)Pins 5–8: GND (Black)Pin 9: +12V DC (Yellow)Pin 10: KEY (Empty)Pin 11: −12V DC (Brown)Pin 12: +5V USER (Fused +5V)Pin 13: −5V DC (White)Pin 14: TICK (50/60Hz TTL) |
Pins 1–4: +5V DCPins 5–9: GNDPin 10: /PWR_FAIL (Power Good)Pin 11: −5V DCPin 12: +5V USERPin 13: −12V DCPin 14: +12V DCPin 15: TICK (50/60Hz TTL) |
Pin 1: +5V DC (Red)Pin 2: +5V DC (Red)Pin 3: KEY (Empty Pin!)Pin 4: GND (Black)Pin 5: +12V DC (Yellow)Pin 6: −12V DC (Blue/White)(+Separate 2-pin PG/Power Good header!) |
Using a Modern ATX / SFX PSU Adapter on A2000 / A3000 / A4000:
• On an Amiga 2000 with an ATX adapter that doesn't generate TICK, simply move motherboard jumper J300 from Pins 1–2 to Pins 2–3 (uses internal VSYNC for the CIA clock)!
• On an Amiga 3000, make sure your ATX adapter includes a small 555 / crystal 50/60Hz TICK oscillator circuit on Pin 15 (or move jumper J350 to VSYNC)!
• On an Amiga 4000D, the motherboard already uses VSYNC internally (no TICK pin on the 6-pin PSU header!), making ATX/SFX conversion super clean.
23-Pin RGB Video (DB23M) & A3000 15-Pin VGA 15kHz RGB + 31kHz Amber
All Big-Box Amigas share the standard 23-pin D-Sub RGB VIDEO port (plus A2000/A3000/A4000 ATX TICK Power Headers, DB23 External Floppy, and DB25 Serial), while the Amiga 3000 adds a second 15-pin High-Density VGA socket (DISPLAY ENHANCER) driven by the built-in Amber flicker-fixer:
| Port / Switch | Key Pins & Bench Notes |
|---|---|
| DB23 RGB Port (All Big-Box Amigas) |
Pin 3 = Red, Pin 4 = Green, Pin 5 = Blue (0.7 V 75 Ω), Pin 10 = CSYNC, Pin 11 = HSYNC, Pin 12 = VSYNC, Pins 16–20 = GND, Pin 22 = +12V (100mA), Pin 23 = +5V (100mA). Note: Always buffer Pins 10/11/12 or use a 330–470 Ω series resistor on CSYNC to SCART Pin 20! |
A3000 Rear VGA Port & Switch (SW499) |
Standard 31.5 kHz 50/60 Hz VGA pinout (Pins 1, 2, 3 = R, G, B, Pin 13 = HSYNC, Pin 14 = VSYNC). Rear slide switch SW499 toggles the Amber scan-doubler ENABLED (31 kHz) vs BYPASSED (15 kHz pass-through). Note: Most modern LCDs need a monitor that supports 50 Hz vertical refresh at 31 kHz on PAL A3000s! |
Zorro II / Zorro III, Video Slot & CPU Fast-Slot Architecture
Key signals on the 100-pin Zorro II/III AutoConfig expansion bus, inline Video Slot, and 86-pin / 200-pin CPU Accelerator slots.
100-Pin Zorro II / Zorro III Expansion Slot AutoConfig • 16-Bit / 32-Bit
Dave Haynie's 100-pin Zorro III bus uses clever address/data multiplexing during 32-bit Zorro III cycles to fit a full 32-bit 3.2 GB address space and 32-bit data path inside the exact same 100-pin physical connector as 16-bit Zorro II — allowing 16-bit Zorro II cards and 32-bit Zorro III cards to coexist in any slot!
| Zorro Pin Group | Pin Numbers | Function & Diagnostic Notes |
|---|---|---|
| +5 V DC Supply | Pins 5, 6, 99, 100 | Regulated +5 V (max 2.0 A per slot) |
| −5 V / +12 V / −12 V | Pin 8 (−5V), Pin 20 (+12V), Pin 10 (−12V) | Auxiliary analog / serial / op-amp rails |
| Digital Grounds | Pins 1–4, 12, 22, 31, 43, 55, 67, 75, 87, 97 | Interleaved ground shield pins |
| AutoConfig Daisy-Chain | Pin 11 (/CFGOUT) & Pin 13 (/CFGIN) | CRITICAL! At boot, each Zorro card maps at $E80000 when /CFGIN is low, gets assigned its base address by expansion.library, and then asserts /CFGOUT low to configure the next slot! (Empty slots automatically bridge /CFGIN to /CFGOUT via motherboard resistor networks). |
Clocks (7M, CDAC, E) | Pin 15 (CDAC), Pin 19 (E), Pin 50 (7M) | System clocks (7.09/7.16MHz & 0.7MHz 6800-style E clock) |
| Address / Multiplexed Z3 Bus | Pins 35–42, 44–49, 57–66 (A1–A23 / AD8–AD31) | 24-bit address in Zorro II mode; multiplexed 32-bit address/data in Zorro III mode |
Data Bus (D0–D15) | Pins 68–74, 76–84 (D15–D0) | 16-bit data in Zorro II; low 16 bits (AD15–AD0) in Zorro III |
Bus Control (Super Buster) | Pin 14 (/C3), Pin 16 (/C1), Pin 17 (/OVR), Pin 25 (/BERR), Pin 89 (/AS), Pin 94 (/DTACK), Pin 96 (/DOE) | Managed by Buster (A2000) or Super Buster (A3000/A4000). A dirty Zorro riser connector on A4000 (CN600) causes instant Yellow/Black screens! |
Video Slot (Flicker-Fixer / RTG / Video Toaster) & CPU Fast Slots
- Amiga 2000 / 3000 (36-Pin) vs Amiga 4000 (36+16-Pin Extended) Video Slot:
- Positioned inline with one of the Zorro slots so a single card (like an Indivision ECS/AGA, Picasso IV, CyberVision 64/3D scandoubler, or RGBtoHDMI) can plug into the Video Slot directly!
- On the A2000 and A3000, the 36-pin Video Slot carries 12-bit digital OCS/ECS RGB (
R0–R3, G0–G3, B0–B3), analog RGB,CSYNC/HSYNC/VSYNC, pixel clock (XCLK/XCLKENfor genlocks), and Left/Right audio! - On the A4000, an extra 16-pin rear extension adds the lower 12 bits of the 24-bit AGA digital video bus (
R4–R7, G4–G7, B4–B7from Lisa) plus 28 MHz pixel clocks!
- CPU / Co-Processor Accelerator Slots:
- A2000 (86-Pin Card-Edge Slot
CN600): Accepts 68020/68030/68040/68060 + 32-bit Fast RAM + SCSI/IDE accelerators (e.g. GVP G-Force, Blizzard 2060, TF536 adapter, Pistorm2K). - A3000 & A4000 (200-Pin High-Density Kel/Molex Connector): Carries the full 32-bit 68030/68040 processor bus. Note: While electrically almost identical between A3000 and A4000, the physical card bracket height and onboard 68030 disable jumper differ (
A3640/CyberStorm MK-II/III/PPC/BFG9060fit both!).
- A2000 (86-Pin Card-Edge Slot
Custom Silicon & Kickstart ROM Reference
Interactive IC Pinout Finder cards plus Big-Box custom chip part numbers and 16-bit vs 32-bit Kickstart EPROM layouts.
Motorola 68000 – 68060
MC68000 (A1000/A2000), MC68030 (A3000/A4000CR), MC68040 (A3640), and MC68060 (accelerators).
View 68000 Pinout →MOS 8520A CIA (×2)
Even (CIA-A) & Odd (CIA-B) Complex Interface Adapters (DIP-40 on A1000/A2000/A3000; PLCC-44 on A4000).
MOS 8372A / 8375 Fat Agnus
25-channel DMA controller, Blitter, Copper, and 512KB/1MB/2MB Chip RAM address generator.
View PLCC-84 Pinout →MOS 8362 / 8373 Denise
OCS Denise & ECS Super Denise — 12-bit digital RGB output, 8 sprites, HAM6/EHB, and mouse quadrature counters.
View Pinout →MOS 8364 Paula
4-channel 8-bit DMA stereo audio, MFM floppy controller, /IPL0–2 interrupt controller, and Right Mouse Button (POT0Y).
Chip & Fast DRAM
41256 / 414256 DIP DRAMs (A1000/A2000), 1M×4 ZIPs (A3000), and 72-pin FPM SIMMs (A4000).
View DRAM Pinout →Big-Box Custom Chip Part Number Matrix
| Chip Role | A1000 / A2000 | A3000 (ECS 32-Bit) | A4000 (AGA 32-Bit) |
|---|---|---|---|
| Chip RAM DMA | 8361/8367 (A1000)8370/8371/8372A/8375 (A2000) |
8372B (2MB Agnus) ( 318069-03) |
Alice (391010-01)(2MB AGA DMA) |
| Video Display | 8362 (OCS Denise) or8373 (ECS Super Denise) |
8373 (ECS Super Denise) + Amber ( 390538) |
Lisa (391227-01)(24-bit AGA Video) |
| Audio & Floppy | 8364R4 / R7 (Paula, DIP-48) |
8364R7 (Paula, DIP-48) |
391077-01 (Paula, PLCC-52) |
| Bus & Zorro Logic | 5719 (Gary) + 5721 (Buster) |
Fat Gary + Ramsey + Super Buster + Super DMAC |
Fat Gary + Ramsey + Super Buster-11 + Bridgette |
Single-Chip (16-Bit) vs Dual-Chip (32-Bit) Kickstart EPROM Guide
When burning Kickstart 3.1 / 3.1.4 / 3.2.2 or DiagROM EPROMs, pay close attention to whether your Amiga uses a single 16-bit ROM or a pair of 32-bit HI/LO ROMs:
| Machine | ROM Sockets | Required 16-Bit EPROMs (512KB Kickstart) |
|---|---|---|
| Amiga 2000 ( U500, 16-Bit Bus) |
1× 40-Pin DIP Socket | 1× 27C400 (512 KB, 256K×16, 40-pin)!Note on Rev 4.x / early Rev 6.0 A2000s: Pin 1 and Pin 31 on the 40-pin ROM socket require the standard A500 Rev 5 Pin 1 → Pin 31 + Pin 21 → Pin 31 jumper wire (fixed on Rev 6.2+)! |
| Amiga 3000 ( U180 & U181, 32-Bit Bus) |
2× 40-Pin DIP Sockets (HI Word + LO Word) |
2× 27C400 (or 27C200 256 KB each) — 16-bit word-interleaved (U180 = Bits 16–31, U181 = Bits 0–15). Set ROM timing jumpers J180/J181 to match mask ROM vs standard 120ns EPROM pinout! |
| Amiga 4000D / 4000T ( U175 & U176, 32-Bit Bus) |
2× 40-Pin DIP Sockets ( U175 = HI, U176 = LO) |
2× 27C400 (100ns–120ns) direct drop-in! (Ensure J151 ROM speed jumper is set appropriately). |
Resources & Further Reading
Blog posts, interactive bench tools, and essential Big-Box Amiga schematics & communities.
Smiggy's Amiga Posts
Bench Tools & Machine Hubs
- IC Pinout Finder — 68000, 6526/8520, 4164 & more
- Connector Pinout Directory — DB23 RGB Video, A2000/3000/4000 ATX Power, DB23 External Floppy, DB25 Serial
- Recap & Repair Reference — capacitor replacement guide
- Ohm's Law Calculator
- Amiga Machine Hub (A500/A600/A1200)
- C64 Machine Hub — Commodore 64 reference
- C128 Machine Hub — C128, C128D & DCR reference
- SX-64 Machine Hub — Executive Portable C64 reference
- Atari ST Hub — 520ST, 1040STFM & STE reference
- Apple IIe Hub — Unenhanced, Enhanced & Platinum reference
- BBC Micro Hub — Model B, B+ & Master 128 reference
- Acorn Atom & Electron Hub — Atom & Electron reference
- ZX Spectrum Hub — 16K/48K & +2/+3 reference
- Sinclair QL Hub — 68008, Microdrive & ULA reference
- Dragon 32/64 Hub — Dragon 32 & 64 reference
- Oric-1 & Atmos Hub — Oric 6502A & ULA reference
- Amstrad CPC 464 Hub — CPC 464 & Datacorder reference
- Amstrad CPC 6128 Hub — 128K & 3″ disc reference
- MSX Machine Hub — MSX1, MSX2, MSX2+ & Turbo R reference
- Osborne 1 & Kaypro II Hub — CP/M luggable reference
- Atari 8-Bit Hub — 400/800, 800XL & 130XE reference
- VIC-20 Machine Hub — Commodore VIC-20 reference
- Commodore PET Hub — PET 2001, 4000 & 8000 reference
- Plus/4 & C16 (TED) Hub — C16, C116 & Plus/4 reference
- TRS-80 & CoCo Hub — Model I/III/4 & CoCo 1/2/3 reference
- TI-99/4A Machine Hub — 16-bit TMS9900 & PEB reference
External Big-Box Amiga Resources
- AmigaPCB.org — interactive trace-by-trace PCB explorer for A2000, A3000, A4000 & A3640!
- AmigaWiki Schematics — official Commodore A1000, A2000, A3000, and A4000 service manuals
- Big Book of Amiga Hardware (BBOAH) — Zorro II/III card settings, jumpers, and accelerator database
- English Amiga Board (EAB) — active Big-Box hardware repair and reproduction PCB community
Big-Box Amiga (A1000–A4000) — Capacitor & Recap Reference
Board revisions, electrolytic capacitor lists, voltage/farad ratings, and Through-Hole & SMD (A4000) servicing notes.
Big-Box Amiga (A2000 / A4000) — A2000 Rev 6.2 & A4000 Rev B
Zorro II / Zorro III workstation mainboards • Mount: Through-hole (A2000) / SMD (A4000) • Difficulty: Expert
Amiga 4000 Rev B Mainboard (12 Capacitors)
| Ref | Capacitance | Voltage | Package / Type | Circuit Location & Bench Notes |
|---|---|---|---|---|
C144 |
47 uF | 16 V | SMD | |
C186 |
47 uF | 16 V | SMD | |
C303 |
22 uF | 25 V | SMD | |
C304 |
22 uF | 25 V | SMD | |
C305 |
10 uF | 25 V | SMD | |
C306 |
100 uF | 6.3 V | SMD | |
C324 |
22 uF | 25 V | SMD | |
C334 |
22 uF | 25 V | SMD | |
C407 |
10 uF | 25 V | SMD | |
C409 |
100 uF | 6.3 V | SMD | |
C811 |
470 uF | 16 V | Radial | |
C812 |
470 uF | 16 V | Radial |
Amiga 2000 Rev 6.2 Mainboard (9 Capacitors)
| Ref | Capacitance | Voltage | Package / Type | Circuit Location & Bench Notes |
|---|---|---|---|---|
C303 |
22 uF | 25 V | Radial | |
C304 |
22 uF | 25 V | Radial | |
C306 |
10 uF | 25 V | Radial | |
C307 |
470 uF | 16 V | Radial | |
C324 |
22 uF | 25 V | Radial | |
C334 |
22 uF | 25 V | Radial | |
C401 |
3300 uF | 16 V | Axial | |
C402 |
3300 uF | 16 V | Axial | |
C811-C816 |
100 uF | 25 V | Radial |
Complete Diagnostic Flowchart: Amiga 500/600/1200 Boot Color Code, Chip RAM & Audio/Video Isolation (Commodore Amiga 500 (Rev 3/5/6A) / A600 / A1200)
Big-Box Amiga (A1000–A4000) — System Bench Tools & IC Pinouts
Click any chip below to open its interactive DIP/PLCC pinout diagram, pin-by-pin signal table, and oscilloscope test waveforms.
74LS244
SN74LS244N / DM74LS244
Octal 3-state buffer/line driver — two 4-bit groups with separate active-low enables, interleaved down the package.
Open Interactive Pinout →74LS245
SN74LS245N / DM74LS245
Octal bidirectional 3-state bus transceiver — one direction pin and one active-low enable, the standard bidirectional bus driver.
Open Interactive Pinout →74LS373
SN74LS373N / DM74LS373
Octal transparent latch with 3-state outputs — level-sensitive latch enable on pin 11, the standard address latch for multiplexed buses.
Open Interactive Pinout →74LS374
SN74LS374N / DM74LS374
Octal edge-triggered D flip-flop with 3-state outputs — rising-edge clock on pin 11, the standard registered bus driver.
Open Interactive Pinout →CD4093
CD4093B / MC14093 / HEF4093
Quad 2-input NAND gate with Schmitt-trigger inputs — CMOS, follows the CD4011 pinout, the cure for slow or noisy input edges.
Open Interactive Pinout →Motorola 68000
MC68000 / MC68HC000
16/32-bit CPU at the heart of the Amiga, Atari ST, original Macintosh and Sega Mega Drive.
Open Interactive Pinout →MOS 6526 CIA
MOS 6526 / 6526A / 8521
Two 8-bit I/O ports, two timers, a time-of-day clock and a serial port — the C64 peripheral chip.
Open Interactive Pinout →MOS 8372A / 8375 Fat Agnus
MOS 8370 / 8371 / 8372A / 8375 (PLCC-84)
The central DMA, Blitter, Copper and Chip RAM controller of the Amiga 500, 2000 and 3000 — 25 DMA channels, RGA register bus, and 512KB/1MB/2MB Chip RAM addressing.
Open Interactive Pinout →MOS 8362 Denise / 8373 Super Denise
MOS 8362R8 (OCS) / 8373R4 (ECS Super Denise)
The Amiga's Display Encoder — renders 6-bitplane HAM/EHB playfields, 8 hardware sprites, 12-bit (4096-colour) RGB output, and quadrature mouse counters.
Open Interactive Pinout →MOS 8364 Paula
MOS 8364R4 / 8364R7 (DIP-48 & PLCC-52)
The unchanged sonic heart of every Amiga from the 1985 A1000 to the 1992 A4000 — 4-channel 8-bit DMA audio, MFM floppy controller, interrupt controller, UART, and proportional pots.
Open Interactive Pinout →Signal & Trace Visualizer (Scope)
Compare healthy vs. faulty CPU clocks, reset ramps, PLA strobes, and 5V PSU ripple waveforms.
Disassembler & ROM LabRetro File Utilities (Rust/Wasm)
6502/6510 disassembler with IC register links, C64 .D64 parser, and EPROM CRC32 verifier/patcher.
Logic & PinoutsConnector & Port Pinout Reference
59 interactive RGB SCART, DIN A/V, PSU polarity, joystick, floppy, and expansion bus pinouts.
Logic & PinoutsLogic & RAM Substitution Guide
Cross-reference 4116→4164 DRAM mods, 2364→27C256 EPROM adapters, and 74LS/74HCT swaps.