Amiga 2000

Resources

Wiki
Schematics

Internals

Motherboard

Keyboard

Amiga 2000 keyboards are rare to get and become more and more pricey. The most popular failure of the keyboard is due to wearing out of the conductive coating on the bottom of rubber contacts inside the keyboard. It is possible to replace them with similar rubbers from Amiga 500 keyboard. The key mounting pods are different and can’t be interchanged.

Reassembly

Configuration

The final configuration of my Amiga 2000 that is stable:

Amiga 2000 Upgrades

Silent Fan

The original fan in the power supply is pretty noisy. Nowadays it is possible to get much more silent fans, which provide similar air flow. I replaced my fan with Noctua NF-R8 Redux 1200.

Gotek USB Floppy Emulator

The most convenient way of transferring disk images to Amiga seems to be through a Gotek USB Floppy Emulator, which uses USB pendrive for disk images storage. Gotek replaces well one of the original floppy drives, though it has a smaller front panel, so some ugly spacing around the drive remains. I haven’t found any off the shelf adapter, definitely 3D printing may be an option here.

If Gotek is to be used as a primary floppy booting device, it should go as DF0, after the connecting tape twist (at the end). The other floppy drive, DF1, should be attached before the tape twist.

DSC_0009

Eliminating Unnecessary Floppy Rotation

With silent fan installed in the power supply and Gotek USB Floppy Emulator as a primary floppy drive, the whole setup is very quiet. It becomes audible, that the second floppy motor is activated any time the other drive (Gotek) is accessed. This is because both floppies in Amiga share a single motor on signal (MTR0D). If this sound effect is annoying, we can eliminate it with a simple floppy mod.

Amiga has two signals on floppy connector to control each floppy: SELx and INUSEx. INUSEx becomes active before the data is transferred to/from floppy x and when it is active SELx controls the validity of the data on the bus. MTR0D seems to be actually = INUSE0 OR INUSE1 (logically). In order to enable the motor of drive 1 only when this drive is used, we need to remove the drive’s motor on signal from MTR0D and attach it to INUSE1. It can be done at the cable connection on the floppy board.

Dual Kickstart

It is convenient to have Kickstart 1.3 and a newer one, preferably 3.1, ready for use without the need to swap the ROM chips. If you own these Kickstart images, you can actually save them to a single larger chip and mount a switch to select between the two images.

By default, Amiga 2000 (and 500, 600) has a 512 kB (4 Mbit) ROM chip installed. This chip uses 18 address pins (A0-A17) to select 2-byte words. We can replace this chip with a larger 2 MB (16 Mbit) chip – M27C160. It has two extra pins to extend the address range: A18 and A19. Fortunately these pins are added as a new row and the rest of the pins is compatible with the smaller version. So we can insert M27C160 into Amiga ROM socket with two extra pins hanging outside the socket. A19 needs to be soldered to the ground pin and A18 will be used to select between two Kickstarts (banks) inside the ROM. We need to connect A18 through a switch that would connect it to the ground or power pin. Now, one Kickstart image needs to be written to the ROM at the address 0x0 and the other at the address 0x80000 (in bytes) or 0x40000 (in words).

Battery Upgrade

By now the original battery would be at best discharged, at worst exploded leaking and damaging the motherboard. It makes sense to install a replaceable battery installed in a cradle.

Chip Memory Upgrade

The original 1MB of Chip RAM can be extended to 2MB max. It can be done with 2MB Chip RAM Adapter board that plugs into Agnus socket and connects to Gary chip.

Fast Memory Upgrade

Amiga 2000 can address maximum of 8MB of Fast RAM. (There is an exception for the memory attached directly to the CPU on the accelerator card, where this limit does not apply, but this memory can’t be used for DMA transfers over Zorro bus). I got the best results in terms of stability from using A2052 2MB expansion board from Commodore.

There are many alternatives from many vendors. I tried one called COLSP, where you can configure up to 8 MB of extra RAM, but I found this board to be unstable when combined with A2630 accelerator and A2090 SCSI controller.

CPU Accelerator

MC68000 CPU can be upgraded with CPU accelerator cards fit into a special accelerator slot on the motherboard. A2630 is a card from Commodore that upgrades Amiga 2000 to MC68030 CPU, MC68882 FPU and up to 4MB of RAM.

Problems with my A2630 started when I added SCSI controller to the system and installed a total of 4MB on the accelerator. Amiga would hang frequently during disk access, which most probably was due to the issues with DMA transfers. It worked perfectly in 68000 mode though.

A closer look at the board revealed that the resistor packs RP100 to RP103 terminating the address lines were soldered incoherently – three of them would pull the lines down to the ground and one was pulling it up to VCC. Commodore used 10-pin resistor packs and it always provided ground and VCC to the marginal pins, with actual lines in between. This has an advantage that by simply reversing the resistor pack we can switch between pulling the lines up to VCC and down to the ground. The disadvantage is that there is always a dummy resistor between ground and VCC, draining unnecessary power. With 8 such resistor packs rated at 1K the current drain is about 40mA, for no reason. I installed 9-pin packs instead and pulled all address lines up to VCC. This removed the stability issues. I also installed other fixed as advices in this article, though they did not improve anything.

Video Scan Doubler

Commodore A2320 Display Enhancer can be used to eliminate the interlacing effect and connect VGA monitor with 31 kHz horizontal frequency over 15-pin VGA connector.

HDD Controller

The most popular HDD standard for A2000 is SCSI. The original Commodore A2090 SCSI controller is the oldest card, but it does not support auto booting. A successor A2090A card has a space for two auto boot EPROMs. On both A2090 and A2090A (without auto boot EPROMs) cards auto boot can be enabled with additional Combitec Autoboot-Karte. Due to difficulties with setup, awkward software and unstable booting I do not recommend using these cards.

A much better solution is Commodore A2091 controller. It has native auto boot support and a space for HDD mounted on the board. To get maximum compatibility and stability, it is absolutely essential to install the latest V7 ROM images on the EPROM chips on the A2091 card (search the Internet for a2091-7.lha to find the ROMs). My A2091 was very stable when combined with A2630 (4MB) and SCSI2SD V5 drive.

An alternative card I tried was Microbotics Hardframe controller. It has a very user friendly disk configuration software, unfortunately I could not make it work with SCSI2SD drive when combined with A2630 (4MB) – it hang on any disk access and never booted correctly.

Hard Disk Drive

The original drive my Amiga came with (as a company to the A2090A controller) was old, huge, heavy and noisy 85 MB Seagate ST-296N. First thing to remove these days from your Amiga.

A good alternative is to use one of 3.5″ Quantum Fireball SCSI drives. It has reasonable capacity (2GB) but is also quite noisy and brings the risk of failure due to its age.

The best solution is to go for a SCSI drive SD card emulator. I used SCSI2SD V5 with a great effect. Regardless of the SD card size, I limited the drive size to 3.9GB.

CD-ROM

It is possible to connect SCSI CD-ROM Drive to any of the SCSI controllers for Amiga 2000. Using CD-ROM with A2091 presents a very annoying issue – the controller will attempt to boot from it before the HDD and if there is no media in the drive, it will wait for the full timeout to happen. This delays each machine boot by about 30 seconds. This issue does not occur with other controllers I tried, but since they are unstable, I decided to remove CD-ROM drive from my setup. I don’t really have any compact disks to use with it anyway.

If you want to use SCSI CD-ROM drive in your setup, AmiCDROM software is a great add to Workbench 3.1. It seamlessly integrates CD-ROM with the OS for data transfer as well as CD audio.

Operating System

Original Workbench 1.3 that comes with Amiga 2000 is pretty useless. I think the best OS for Amiga 2000 is Workbench 3.1. It is fast, consumes little memory and covers all the functionality that Amiga 2000 can provide. There is a variety of mods and upgrades to it to make it look attractive and functional. I installed and use two of them: BetterWB and MagicWB.

I think it makes no point to install Workbench 3.9 on Amiga 2000. You will not get all the graphics features it can give due to lack of the AGA chip. It will consume a lot of memory and will be visibly slow, even with the accelerator.

Display Monitor

The way to go for Amiga 2000 is to use a CRT display. LCD flat screens don’t match the design at all and the screen looks bad on them, they miss this little blurring and emphasize all the imperfections of the display. The native resolution also will likely not match and they may give you ugly scaling effects.

The most popular Commodore monitors will support 15kHz horizontal sync frequency only. They will not work with A2320 scan doubler and high resolution.

The reasonable choice is other vendor’s multi-sync CRT monitor supporting 31kHz horizontal sync. I use Samsung SyncMaster 755DFX and it both looks well and runs well with my Amiga.

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