RetroWiki

This is the workhorse of the series. While the A1000 introduced the world to Amiga and the A500 was the gamer edition the Amiga 2000 was expandable, high performance, high price, and had the chops for the new field of video production.

• A2000 Motherboard Revisions

Chips

• Agnus
  • the name Agnus is derived from 'Address GeNerator UnitS' since it houses all address registers and controls memory access of the custom chips
  • manages all RAM intereactions
  • blitter - a sub component is responsible for
  • copper - a sub component is a co-processor for
• Buster
  • is the DMA arbitrary controller
• Denise
  • the name Denise is a contrived contraction of Display ENabler
• Gary
  • system address decoder
• Paula
  • the name Paula is contrived contraction of Ports, Audio, UART and Logic, and coincidentally the chip designer's girlfriend

Size

While not exact, these should be close enough for most .

• motherboard
  • 360mm deep x 414mm wide x 25mm high, overall or
  • 14 3/8“ deep x 16 1/2” wide x 1“ high, overall
  • depth is from the front db9 shroud to the back of the db23 shroud(s)
  • the highest component is the keyboard connector
  • the bottom mobo RF shielding flexes so the height is close but not always exact
  • slot cut-out, by the rear slots
    • 15mm deep x 150mm wide or
    • 5/8” deep x 5 15/16“ wide

Next we have some odd collected data. To me, the important info is Part Number. The Rough Date is literally that. I look at most of the custom chips and pull the date code off of them. I then add a month or two (production of chips + shipping + build time) to get the Rough Date.

• Floppy Disk Drives (FDD)
• Hard Disk Drives(HDD)

• Recap
• Power notes for all Amigas

• Blank screen, things to check
  • check Agnus is seated correctly, re-seat if necessary
  • swap KS ROM
  • swap in CIA chips, swap one at a time
  • no instant red means that the KS ROM is being read OK and the checksum has passed
• Yellow indicates
  • memory issue so remove any memory expansions if present
  • yellow/green can sometimes be cured by re-seating Agnus
• Gray screen
  • most likely chip RAM
• Red screen

CIA 8520 common failure symptoms are:

• dead or flakey floppy drive. DF0:???, icons for nonexistent drives showing up, motor always on, head step problems, etc.
• dead or flakey parallel port
• no mouse/joystick fire buttons. (left mouse=fire)
• TOD clock not advancing, or only advances a few seconds and resets.
• CLI works okay, but double-clicking on WB icons hangs WB.
• keyboard problems about 30% of the time. Usually it's a bad 6570 micro in the keyboard.
• data errors on the floppy or serial ports are not necessarily 8520 failures. The data from these devices goes to Paula, and in owning and tinkering with Amigas since 1986, I've never seen a bad Paula.
• joystick or mouse directional failure is NOT 8520 related. This is a common misconception. Probably the fuse that looks like a resistor
• CIA at U8 is responsible for the floppy select, motor enable and head step functions
• CIA at U7 is for disk change, track 0 selection, the ready signal and write protect
• C64's 6526 and Amiga 8250 are basically compatible and swappable - one difference is 4 byte BCD time of day counter being replaced with (much more useful) 3 byte binary counter

Real Time Clock not working

• you set the DATE then try to SAVE it only to have a 'Can't find battery-backed up clock'
  • 1> DATE 07-May-2023
  • 1> SETCLOCK SAVE

• convert A2000 OCS to ECS
  • do it? nah, a fun project but little reward
  • replace Agnus with a FAT(1MB) or FATTER(2MB) version
    • an Agnus 8372B (found in A3000s)
    • an Agnus 8375 + adapter (there are a few pinouts different from 8372)
    • for gaming you only need a 1MB Agnus, there are not many games built for ECS
    • for video production you need a 2MB Agnus
  • Super-Denise (ECS) 8373 R4
    • a drop in replacement
• 68010
  • do it? yup, it's easy, non-destructive, and you get a mini boost
  • the 68010 has extra instructions programmed into the CPU
  • it does some fancier calculations, for instance compression
  • just pull the 68000 and install the 68010
  • testing will show a 5-10% improvement in performance, it so minimal that you may not see the change
  • there are rumors that some programs which require a 68020 will run on a 68010, this goes back to the extra instructions in the 68010 CPU
  • there may be problems with some games which can be solved by a software patch (decigel), the patch has to be loaded first
• NTSC/PAL switch
  • do it? yup, it's easy, non-destructive, and allows some bitchin PAL demos
  • there is a solder blob (some may have a jumper) on J102, which is grounded
  • desolder that, and solder two wires to an on/off switch
  • you can drilled a hole in one of the slot covers, install a small switch, then it's a reach-around to enable the NTSC/PAL mode
  • if you have a Gotek drive in place, install the switch there, I like a bunch of switches and blinky lights on things