Atari 65XE Troubleshooting Guide
This guide covers detailed troubleshooting of the Atari 65XE 8-bit home computer. It addresses typical failure symptoms, diagnostic steps and component-level remedies for common faults affecting PAL and NTSC models. Use these procedures to restore a non-booting, unstable or otherwise faulty 65XE to reliable operation.
Preliminary & Power-up Checks
[edit | edit source]Begin with basic power and visual checks before suspecting major component failure.
- Disconnect all peripherals (cartridges, SIO, joystick, cassette).
- Remove the top cover; inspect for burnt, cracked or corroded components—especially around the power jack, voltage regulator, and mainboard edge connectors.
- Confirm the power supply outputs +5V DC (measure at the power input or across any major IC’s Vcc and GND pins).
- Inspect for leaking or bulging electrolytic capacitors, especially C56 (input filter) and C57 (regulator output).
- Check for loose or oxidised IC sockets (RAM, ROM, custom chips).
- Ensure the power switch is not intermittent or oxidised.
Power Supply & Voltage Table
[edit | edit source]| Test Point | Expected Voltage | Notes |
|---|---|---|
| Power input jack (centre) → GND | +5 V DC (±5%) | Main logic supply |
| 7805 regulator input (pin 1) | 8–12 V DC | From external PSU |
| 7805 regulator output (pin 3) | +5 V DC | Should be stable under load |
| Any IC Vcc pin | +5 V DC | Check at RAM, CPU, GTIA, ANTIC |
Common PSU faults:
- No power-on LED, no video – check PSU fuse, cable, and 7805 regulator.
- Repeated resets, random crashes – suspect dried-out capacitors or failing 7805.
- Overvoltage (>5.5 V) – can destroy RAM or custom ICs rapidly.
Display & Chime Diagnostics
[edit | edit source]The 65XE should display a blue READY prompt and beep on successful boot. If not, use the following table to narrow down the fault:
| Symptom | Likely Cause | Action |
|---|---|---|
| No video, no sound, power LED off | Dead PSU, blown fuse, bad switch | Test/replace PSU, check fuse, clean switch |
| Black screen, power LED on | RAM, CPU, ROM, or custom chip failure | See “Black Screen” flowchart below |
| Solid colour screen (no text) | ROM or RAM fault | Reseat/replace ROM, test RAM |
| Garbage characters, unstable display | RAM fault, bad socket, bus contention | Swap/test RAM, clean sockets |
| Rolling/no sync video | Bad GTIA, ANTIC, or crystal | Swap GTIA/ANTIC, check clock |
| No beep at power-on | Bad POKEY, speaker, or CPU | Test/replace POKEY, check speaker wiring |
“Black Screen” (No Boot) Flowchart
[edit | edit source]- Confirm +5 V at mainboard and ICs.
- Check for a brief beep or click at power-on (if present, CPU/ROM likely running).
- Swap/feel GTIA, ANTIC, CPU (6502C), and POKEY in turn (if socketed).
- Reseat or substitute OS ROM and BASIC ROM.
- Test RAM chips (see below).
- Inspect for shorted decoupling capacitors or burnt resistors near the power input.
Memory & ROM Faults
[edit | edit source]The 65XE uses eight 4164 DRAMs (U12–U19) and two ROMs: OS (U3) and BASIC (U4). RAM and ROM failures are among the most common causes of boot problems.
RAM Faults
[edit | edit source]| Symptom | Probable Cause | Action |
|---|---|---|
| Black screen, no beep | Lower RAM failure (U12–U15) | Replace suspected DRAM(s) |
| Garbage screen, freezes | Upper RAM failure (U16–U19) | Replace DRAM(s), check address lines |
| Random characters, “Error” on boot | Partial RAM failure | Swap/test RAM, check for hot chips |
Diagnosis:
- Touch each DRAM after 1–2 minutes – a failed chip may run hot.
- Piggy-back a known-good 4164 on each suspect chip; if boot improves, replace the underlying chip.
- Use a RAM test cartridge (e.g. Atari Diagnostics, SALT) for precise identification.
ROM Faults
[edit | edit source]| Symptom | Probable Cause | Action |
|---|---|---|
| Blue screen, no READY prompt | BASIC ROM failure (U4) | Replace BASIC ROM |
| No display, no beep | OS ROM failure (U3) | Replace OS ROM |
| Boots cartridge but not to BASIC | BASIC ROM bad | Replace BASIC ROM |
Note: Cartridges override internal ROMs; if a cartridge boots but normal BASIC does not, the fault is in the OS or BASIC ROM.
Connector & Socket Issues
[edit | edit source]Many 65XE faults are due to poor connections, especially after years of use.
- Reseat all socketed ICs (RAM, ROM, custom chips).
- Clean edge connectors (cartridge, SIO, joystick) with isopropyl alcohol.
- Inspect for cracked solder joints at the power jack, SIO, and joystick ports.
- Check for broken traces near the keyboard connector and cartridge slot.
- Test continuity from each port pin to its corresponding PCB pad.
Component-level Tests
[edit | edit source]Clock & Reset Signals
[edit | edit source]- Confirm system clock (1.79 MHz NTSC / 1.77 MHz PAL) at pin 39 of the 6502C CPU.
- RESET line (CPU pin 40) should pulse low at power-on, then remain high (+5 V).
- If no clock, suspect the crystal (Y1), GTIA, or ANTIC.
- If RESET stuck low, check C50, R114, and associated reset circuitry.
Voltage Test Points
[edit | edit source]| Location | Expected Voltage | Notes |
|---|---|---|
| 6502C Vcc (pin 8) | +5 V DC | Main CPU supply |
| GTIA Vcc (pin 24) | +5 V DC | Video logic |
| DRAM Vcc (pin 8) | +5 V DC | All RAM chips |
Audio & I/O Failures
[edit | edit source]The POKEY chip (U7) generates sound and handles keyboard, serial, and paddle input.
| Symptom | Likely Cause | Action |
|---|---|---|
| No sound, but boots | Bad POKEY, speaker, or amp | Replace POKEY, test speaker |
| Keyboard unresponsive | Bad POKEY, keyboard membrane, or connector | Test/replace keyboard, check POKEY |
| Joystick port not working | Bad solder joint, trace break, or POKEY | Reflow joints, continuity test, replace POKEY |
| SIO (disk/tape) not detected | SIO connector, POKEY, or 74LS logic | Clean connector, check U5/U6 (logic) |
- Test the speaker by applying 1.5 V briefly; if it clicks, the speaker is good.
- For keyboard faults, test continuity from the keyboard connector to the POKEY IC.
Cartridge & Peripheral Failures
[edit | edit source]- If the system boots with a cartridge but not without, suspect the BASIC or OS ROM.
- If no cartridge boots, check the cartridge slot for bent pins or cracked solder joints.
- SIO (serial) failures often trace to U5/U6 (74LS logic), POKEY, or the SIO connector itself.
- Cassette motor control issues may be due to Q1 (transistor) or associated driver circuitry.
Error & Code Tables
[edit | edit source]The 65XE does not display detailed error codes, but certain patterns are diagnostic:
| Symptom/Pattern | Interpretation |
|---|---|
| Black screen, no beep | Major RAM, ROM, or CPU failure |
| Blue screen, no READY | BASIC ROM or RAM fault |
| Boots with cartridge only | Internal ROM failure |
| Beep but no display | Video (GTIA/ANTIC) failure |
Final Notes
[edit | edit source]- Always start with power and visual checks.
- Use a known-good power supply and test cartridges for diagnosis.
- Statistically, most common failures: RAM → ROM → POKEY → GTIA/ANTIC → CPU.
- Fit sockets when replacing chips for future serviceability.
- Avoid prolonged operation with a faulty PSU—overvoltage quickly destroys custom ICs.