Editing Atari 800XL Troubleshooting Guide (section)

== Preliminary & Power-up Checks ==

Begin by confirming the '''external power supply''' delivers correct voltages:
* The 800XL requires '''+5 V DC''' (regulated, centre-positive) at the power input.
* If the machine does not power up (no LED, no video, no sound):
  # Test the PSU output with a multimeter before connecting.
  # Inspect the power jack and board for cracked solder joints or corrosion.
  # Check the internal fuse (F1, 1.5 A) near the power input.
  # Examine for burnt, leaking, or bulging capacitors, especially C56 and C57 near the regulator.
  # Verify the power LED (D7) and its series resistor (R180).

{| class="wikitable styled-table"
! Symptom !! Probable Cause !! Action
|-
| No power LED, no video, no sound || Dead PSU, blown fuse, bad power jack || Test/replace PSU; check/replace fuse; reflow jack
|-
| Power LED on, but no video or sound || Faulty voltage regulator (U5, 7805), shorted IC || Test +5 V at U5 output; check for hot chips
|-
| Intermittent power loss || Cracked solder joints, dirty power switch || Re-solder joints; clean or replace switch
|}