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 the `RP5C01` RTC chip!
- CR2032 Coin-Cell + Blocking Diode Replacement: When fitting a non-rechargeable CR2032 holder, you MUST wire a `1N4148` or `BAT85` Schottky 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 `Amber` deinterlacer (`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 (`256KB` on mainboard + `256KB` front 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 (`1MB` total: `512KB Chip + 512KB Slow RAM`).
- Rev 6.0 / 6.2 (Most Common): Upgraded to 8372A (`1MB ECS Agnus`) configuring all 1 MB (8× `414256` 256K×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` / `390539` Rev 7, 9, or 11): Zorro III 32-bit bus arbiter (Always upgrade socketed Rev 7/9 to `Rev 11` for Zorro III DMA stability!)
- Super DMAC (`390537-02 / -04`) + WD33C93A (`00-08` / `16-08` Proto): 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 (`391010` PLCC-84): AGA 2 MB Chip RAM DMA controller
- Lisa (`391227` QFP-84): AGA 24-bit video sprite & bitplane generator
- Paula (`8364` PLCC-52): Audio, floppy & UART controller
- Fat Gary (`390540`) & Ramsey (`390541-07`): 32-bit bus & SIMM Fast RAM controllers
- Super Buster (`390539-11` Rev 11): Zorro III arbiter (soldered QFP on Rev B; socketed PLCC-84 on some boards)
- Bridgette (`391380` QFP-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.
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`/`/DTACK` line 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` `/LED` and releasing `PA1` `/OVL` ROM 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!
- 3. Check A4000 Jumpers `J100` & `J104` + SIMM Socket `U891`: Confirm `J100/J104` match your CPU card (`INT` for A3630, `EXT` for 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 (`390541-04` vs `-07`) & Super DMAC (`-02` vs `-04`): On the A3000, `Ramsey-04` must be paired with `Super DMAC-02` (or `Ramsey-07` with `Super DMAC-04`); mixing `Ramsey-07` with an early `DMAC-02` at 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 OKI `MSM514221` field 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 DC` Pins 5–9: `GND` Pin 10: `/PWR_FAIL` (Power Good) Pin 11: `−5V DC` Pin 12: `+5V USER` Pin 13: `−12V DC` Pin 14: `+12V DC` Pin 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 (see our A500/A600/A1200 Hub for the full 23-pin SCART table), 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`/`XCLKEN` for 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–B7` from 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` / `BFG9060` fit both!).
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).
View CIA Family Pinout →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
- Recap Planner — 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
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