Editing Atari 130XE Troubleshooting Guide (section)

== Preliminary & Power-up Checks ==

Begin with basic power and visual checks before suspecting major component failure.

# '''Disconnect all peripherals''' (cartridges, SIO devices, joysticks, cassette).
# Remove the top cover (five screws underneath); inspect for burnt, cracked or corroded components — especially around the power jack, voltage regulator, bridge rectifier, and mainboard edge connectors.
# Confirm the '''power supply outputs correct voltage''' (see table below).
# Inspect for leaking or bulging electrolytic capacitors, especially the main filter capacitor near the power input.
# Check for loose or oxidised IC sockets (ANTIC, FREDDIE, ROM if socketed).
# Ensure the power switch is not intermittent or oxidised — clean with contact cleaner if necessary.

=== Power Supply & Voltage Table ===

The 130XE uses an external PSU providing approximately 9V AC, which is rectified and regulated onboard.

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:90%; text-align:center;"
! Test Point !! Expected Voltage !! Tolerance !! Notes
|-
| PSU barrel plug output || ~9V AC || 8–11V AC || Measure with multimeter set to AC
|-
| After bridge rectifier (before regulator) || ~12V DC || 10–14V DC || Unregulated, pulsating DC
|-
| 7805 regulator input (pin 1) || ~12V DC || 10–14V DC || Must be >7V for regulation
|-
| 7805 regulator output (pin 3) || +5.00V DC || 4.85–5.15V DC || Main logic supply — critical
|-
| CPU (6502C) pin 8 (Vcc) || +5.00V DC || 4.85–5.15V DC || Verify supply reaches CPU
|-
| ANTIC pin 20 (Vcc) || +5.00V DC || 4.85–5.15V DC || Video DMA processor supply
|-
| GTIA pin 24 (Vcc) || +5.00V DC || 4.85–5.15V DC || Video output chip supply
|-
| POKEY pin 24 (Vcc) || +5.00V DC || 4.85–5.15V DC || Audio/IO chip supply
|-
| DRAM pin 8 (Vcc) — all chips || +5.00V DC || 4.85–5.15V DC || RAM supply — overvoltage kills RAM quickly
|-
| FREDDIE pin 20 (Vcc) || +5.00V DC || 4.85–5.15V DC || Memory controller supply
|}

'''Common PSU faults:'''
* '''No power-on LED, no video''' — check PSU fuse (if present), cable, bridge rectifier, and 7805 regulator.
* '''Repeated resets, random crashes''' — suspect dried-out filter capacitors or failing 7805.
* '''Overvoltage (>5.25V at logic rail)''' — replace regulator immediately; overvoltage destroys DRAM and custom ICs rapidly.
* '''Excessive ripple (>100 mV p-p on +5V rail)''' — recap main filter capacitor (2200 µF) and regulator output cap.