Amiga 2000 Troubleshooting Guide
Fault-finding on the Amiga 2000. Commodore's A2000 service documents are schematics and parts lists without a troubleshooting section.[1] The A2000 shares its custom chips and most of its circuit with the Amiga 500, and Commodore's A500 service manual covers both machines' start-up sequence and its system test disk.[2] Ian Perry's Amiga Troubleshooter chart (1993) gives A2000 designators for every suspect it lists.[3]
Before anything else, take out every expansion card, disconnect extra drives and peripherals, and try the machine with a known good drive.[3] Look at the area round the clock battery BT800 for corrosion; many A2000 faults start there.[4]
Start-up colours
[edit | edit source]Commodore's Kickstart 1.3 start-up sequence for the A500 and A2000:[2]
| Screen | Meaning |
|---|---|
| Dark grey | Hardware set up and screen turned on |
| Red | ROM checksum failure |
| Yellow | Spurious exception before the error handler is set up |
| Green | Memory configuration problem |
| Blue | Custom chip register check failed |
| Light grey | Software running; Workbench prompt follows |
The keyboard reports its own self-test failures by blinking Caps Lock: one blink for a ROM checksum failure, two for a RAM test failure, three for a watchdog timer failure and four for a short between row lines.[5]
Symptom chart
[edit | edit source]Perry's chart, with the A2000 positions he gives:[3]
| Symptom | Check |
|---|---|
| No power-up, black screen | A known good supply; 68000 U100 (too hot to touch means bad); Agnus U101; the oscillator (no clocks) |
| Green screen | Agnus U101; Gary U102; RAM (a chip too hot to touch is bad); the U101 socket |
| Dark grey goes to light grey but no Workbench prompt | CIA U300; Paula U200; R200 (1 Ω); Agnus U101; the 74LS32 chip select (the chart prints U301; Commodore's parts list puts a 74LS32 at U302); the U101 socket |
| Keyboard dead | CIA U300; Agnus U101; Gary U102; R914, the 1 Ω 1/2 W resistor that feeds the keyboard's 5 V |
| Mouse pointer does not move, buttons work | F1, a 4 A pico fuse (Rev. 6 and later); Denise U201; U202 (74LS157) |
| Mouse or joystick dead | U202 (74LS157); Denise U201; U107 (74F04) |
| Left mouse button and fire button dead | CIA U300 |
| Right mouse button dead | Paula U200 |
| Picture breaks up after 15 to 30 minutes | Agnus U101; Denise U201; the U101 socket |
| Locks up when an icon is double-clicked | Agnus U101; Denise U201; CIA U300; U302 (74LS32) |
| Scrambled picture, loss of composite sync | Agnus U101; U205 (74HCT244) |
| Red, green or blue missing | Denise U201; U205, U206 (74HCT244); video hybrid |
| No video at all | Denise U201; video hybrid; U205, U206 |
| Modem will not transmit | U304 (1488); Paula U200; CIA U301 |
| Serial port will not receive | U305 (1489); Paula U200; CIA U301 |
| Printer not working | CIA U301; R318 (47 Ω) |
| Prints wrong characters | CIA U300 |
| Drive not recognised | CIA U301; fuses F3 and F4 (4 A pico) |
| Drive motor problems | CIA U301; Gary U102; U203 (74LS38) |
| Disk change or write protect not detected | CIA U300 |
| Read or write errors | Paula U200; 68000 U100; Agnus U101 |
| Second internal drive (DF1) not recognised | Jumper J301 must be fitted; CIA U301; U900 (74F00); U108 (74LS74) |
| Audio missing on one or both channels | Paula U200; U204 (LF347/TL084); FETs Q200, Q201; cracked joints on jacks CN204, CN205; R233, R243 (1 kΩ) |
A machine runs without −12 V, but the serial port will not work.[3]
Battery damage
[edit | edit source]Corrosion from BT800 typically shows as a clock that will not keep time and a dead or jumpy mouse pointer.[4] It spreads to the 68000 socket and the parts round it; one board had green corrosion on pins 1 to 6 of the CPU socket.[6] Remove the battery, clean the board and test the tracks in that area before suspecting chips. See the maintenance guide.
Power supply
[edit | edit source]- Expansion cards that disappear once the machine is warm have been traced to the supply.[7]
- If the clock or CIA timers misbehave after fitting a replacement supply, check jumper J300: it selects the supply's 50/60 Hz TICK or the video vertical sync as the time base, and the system will not run properly without one.[8]
- Rail ratings and supply faults are on the maintenance page.
Diagnostic software
[edit | edit source]Commodore's A500/A2000 System Test disk runs KEYTEST, SCREENTEST, a HAM picture test for Agnus and Denise faults, an animated cube, and SYSTEST, which tests the clock, the blitter, chip and fast RAM, sprites and the floppy drive. Its documented SYSTEST option strings cover "A500 with A501 or A2000" for board test, burn-in and ageing.[2]
Related pages
[edit | edit source]- Amiga 2000
- Amiga 2000 Maintenance Guide
- Amiga 2000 Capacitor Replacement Guide
- Amiga 500 Troubleshooting Guide
- Battery Explosion, Capacitor or Corrosion Damage
References
[edit | edit source]- ↑ Commodore Business Machines, System Schematics A2000, PN-314135-01, August 1990, hosted at Amiga 2000 System Schematics (314135-01). Parts list for PCB assembly #312720-01, PDF pp. 8-9.
- ↑ 2.0 2.1 2.2 Commodore Business Machines, Service Manual A500, PN-314981-04, October 1990, hosted at Amiga 500 Service Manual (314981-04). A500/A2000 system test, PDF pp. 32-33; Amiga 1.3 start-up sequence, PDF p. 33.
- ↑ 3.0 3.1 3.2 3.3 Ian Perry, Amiga Troubleshooter (1993), original chart at sacc.org; reproduced with A2000 designators as Commodore Amiga problems—link(accessed 2026-10-01)
- ↑ 4.0 4.1 RTC battery replacement—link(accessed 2026-10-01)
- ↑ Commodore-Amiga, Amiga Hardware Reference Manual, appendix G, Keyboard Interface / Power-Up Sequence—link(accessed 2026-10-01)
- ↑ Amiga 2000 battery repair—link(accessed 2026-10-01)
- ↑ [Solved][A2000] no more autoconfig cards when hot—link(accessed 2026-10-01)
- ↑ A2000 jumpers—link(accessed 2026-10-01)