Amiga Troubleshooting Guide
for A500/A2000

POWER UP SEQUENCE

• About 1/2 second delay
• Disable and clear all interrupts
• Dark gray screen
• If ROM bad, screen red
• Temporarily exception processing if artificial exception occurs, screen yellow
• Configure memory if bad, screen green
• Custom IC registers if bad, screen blue
• Restore screen change to light gray, then workbwench prompt

POWER UP PROBLEMS

1. No workbench prompt:
   Screen goes from dark gray to light gray but does not display Workbench prompt. Most probable causes are:
   • 8520 U7 Odd CIA (U300 A2000)
   • 8364 U3 Paula (U200 A2000)
   • EMI 1301 1 ohm resistor (R 309 Rev. 6A/7 boards; R200 A2000)
   • 8370-8372/8375 U2 Fat Agnes (U101 A2000)
   • 74LS32 U37 (chip select) , (U302 A2000)
   • U2 socket
2. No power up (black screen)
   • Substitute a known good power supply to eliminate as a possible source of the problem
   • 68000 U1 (Check for excessive heat. If it is too hot to touch, it is bad) (U100 A2000)
   • 8370-8372/8375 U2 (U101 A2000)
   • X1 Crystal (no clocks)
3. Green screen:
   • 8370-8372/8375 U2 (U101 A2000)
   • 501 or similar RAM expansion
   • 5719 U5 Gary (U102 A2000)
   • RAM on motherboard (Check for excessive heat, if it is too hot to touch, it is bad.)
   • U2 socket (U101 A2000)

A500/2000 KEYBOARD

1. If the caps lock light on the keyboard is flashing when you power up, note the number of times it flashes.
   • 1 flash 6570-036 keyboard controller
   • 2 flashes 6570-036 keyboard controller
   • 3 flashes 555/74LS123/74LS27
     The above chips are located on the keyboard. If you cannot reset the computer [control-amiga-amiga], the most probable cause is Q2. The next most likely cause, 74LS27.
2. If the keyboard is determined not to be the problem, the defect is most likely on the main PCB [A500 monter board or A2000]. The most problematic chips are:
   • U7 Odd CIA[KBdata Pin 39 - KBclock Pin 40](U300 A2000)
   • 8370 -8372/8375 (U101 A2000)
   • 5719 Gary U5 (U102 A2000)
   • R914 1 ohm 1/2 watt resistor A2000 (supplies 5 volts to keyboard)

MOUSE OR JOYSTICK PROBLEMS
A known good mouse and joystick should be used to eliminate them as the source of the problem. If it is determined that the mouse and joystick are okay, the most likely causes are:

1. Mouse does not move, left and right mouse buttons okay, joystick okay.
   • EMI 1401.5 1 ohm resistor (supplies 5 volts to mouse) A2000 Rev 6 and up F1 4 amp pico fuse
   • 8362 U4 (U201 A2000)
   • 74LS157 U15 (U202 A2000)
2. Mouse or joystick not working
   • 74LS157 U15 (U202 A2000)
   • 8362 U4 (U201 A2000)
   • 74F04 U33 (U107 A2000)
3. Left mouse button and fire button on joystick not working
   • 8520 U7 Odd CIA (U300 A2000)
4. Right mouse button not working
   • 8364 U3 Paula (U200 A2000)

VIDEO PROBLEMS

1. Screen breaks up (scrambles) after running for 15 to 30 minutes.
   
   • Probable causes are:
   • 8370-8372/8375 U2 Fat Agnes (U101 A2000)
   • 8362 U4 Denise (U201 A2000)
   • U2 Socket (U101 A2000)
2. System locks up when double clicking on icon
   • 8370/8375 U2 (U101 A2000)
   • 8362 U4 (U201 A2000)
   • 8520 U7 Odd CIA (U300 A2000)
   • 74LS32 U37 (U302 A2000)
3. Scrambled video loss of composite sync.
   • 8370-8372/8375 U2 (U101 A2000)
   • 74HC245 U41 (74HCT244 U205 A2000)
   • RP403
4. Incorrect color (loss of red, green, or blue)
   • 8362 U4 (U201 A2000)
   • 74HC245 U40-U41 (74HCT244 U205-U206 A2000)
   • Video Hybrid
5. No video (black screen)
   • R405 4.7 ohm resistor
   • R406 4.7 ohm resistor
   • 8362 U4 (U201 A2000)
   • Video Hybrid
   • 74HC245 U40-U41 (74HCT244 U205-U206 A2000)

SERIAL PORT PROBLEMS

1. Modem will not transmit. Most likely causes are:
   • 1488 U38 (transmit) (U304 A2000)
   • 8364 U3 Paula (U200 A2000)
   • 8520 U8 Even CIA (U301 A2000)
2. Modem or serial port will not receive
   • 1489 (receive) (U305 A2000)
   • 8364 U3 Paula (U200 A2000)
   • 8520 U8 Even CIA (U301 A2000)

PARELLEL PORT PROBLEMS
A known good printer should be substituted to eliminae it as the source of the problem.

1. Printer not working correctly or not working at all. The most likely causes are:
   • 8520 U8 Even CIA (U301 A2000)
   • EMI 1501 47 ohm resistor (R318 A2000)
2. Prints incorrectly
   • 8520 U7 Odd CIA (U300 A2000)

DISK DRIVE PROBLEMS
Clean the heads and check for excess dust in drive. Clean out dust and try again. This may eliminate the problem. In the following tests, a known good drive should be substituted to eliminate the drive as the source of the problem.

1. Internal/external drive not recognized. Probable causes:
   
   • 8520 U8 Even CIA (U301 A2000)
   • F4 4 amp pico fuse bad (A2000)
   • F3 4 amp pico fuse bad (A2000)
2. Motor problem
   • 8520 U8 Even CIA (U301 A2000)
   • 5719 U5 Gary (U102 A2000)
   • 74LS38 U36 (U203 A2000)
3. Not recognizing disk change
   • 8520 U7 Odd CIA (U300 A2000)
4. Write protect problems
   • 8520 U7 Odd CIA (U300 A2000)
5. Read/Write errors
   
   • 8364 Paula U3 (U200 A2000)
   • 68000 U1 (U100 A2000)
   • 8370-8372/8375 U2 (U101 A2000)
6. DF1 A2000 not recognized
   • J301 open (must have jumper installed)
   • 8520 U301
   • 74F00 U900
   • 74LS74 U108

AUDIO PROBLEMS

• Problem with left,right, or both channels
• 8364 U3 Paula (U200 A2000)
• LF347/TL084 OP-amp U14 (U204 A2000)
• Q331 or Q321 F.E.T. (Q201 (A2000)
• CN3 or CN4 (cold solder connection) (CN205-CN204 A2000)
• EMI 1303 or 1302 (R243-R233 ik ohm A2000)
• Bad connecting cable

You can also check my troubleshooting tips for more help.