Hardware Failure

Sophos AP6 420 smoke smell or burned PCB: Diagnose & Fix

Q: Where can I find the Sophos official documentation?

https://support.sophos.com/support/s/ — search the product family + feature name.

By Sai Kiran Pandrala · reviewed by Sai Kiran Pandrala, Editor Last verified: 2026-05-30

⚡ At a glance

Vendor	Sophos
Operating system	SFOS (Sophos Firewall OS)
Category	Hardware Failure
Skill level	Intermediate to advanced
DIY-able?	Yes with CLI access; some scenarios need Sophos Support + RMA.

When a Sophos AP6 420 starts misbehaving, the temptation is to reboot and hope. Resist it. Capture `system version (CLI)` and `system diagnostics show device-info` first; that 30-second buffer is the difference between a real root cause and another reload at 3am next week.

SFOS (Sophos Firewall OS) has a habit of logging the actual failing component into the system log seconds before the LED transitions. Tail the log while you run the diagnostic commands. you will often see the answer scroll past in real time.

Below is the exact sequence I run on customer gear. Steps are ordered cheapest-first so you exit early if it really is just a loose cable.

What this guide covers

Diagnose and recover from smoke smell or burned PCB on a Sophos AP6 420.

Step-by-step

STOP. Power off the device at the wall before touching it.
Open the chassis and identify which board / module is the source of the smell.
Photograph the visible damage (scorched capacitors, blackened ICs).
Note the device serial number and exact model for the support case.
Do not power back on, burned components fail closed and can damage adjacent boards.
Open a Sophos Support case with the photos and serial.
RMA the affected component (line card, supervisor, PSU) or the full chassis if the backplane is damaged.

CLI / commands

# Verify hardware state
system version (CLI)
system status
system diagnostics show device-info

# Collect for Sophos Support
system support-tools generate-debug-info

When to RMA

Repeated failure after re-seat and power-cycle
Visible burn, scorching, or physical damage
POST or memory diagnostic failure
Hardware crashinfo without a software workaround

Frequently asked questions

Will this work on my specific SFOS (Sophos Firewall OS) version?

The procedure reflects current SFOS (Sophos Firewall OS) behaviour. Older releases may need minor syntax adjustments: use the CLI help (? or tab-completion) to verify.

Should I open a Sophos Support case immediately?

Open one if you suspect hardware failure or the symptom persists after a maintenance-window reload. Make sure your support entitlement is active first.

Where can I find the Sophos official documentation?

https://support.sophos.com/support/s/, search the product family + feature name.

Is this procedure safe in production?

Test in a lab or maintenance window first. Capture pre-change state so you can roll back.

All Sophos fix guides → /sophos/
All vendor guides → /vendors/

Related guides worth a look while you sort this one out:

References

Sophos support portal: https://support.sophos.com
Sophos knowledge base: https://support.sophos.com/support/s/
Sophos security advisories: https://www.sophos.com/en-us/security-advisories
Open a case: https://secure2.sophos.com/en-us/support.aspx

Reference material, not professional advice. Validate against your specific SFOS (Sophos Firewall OS) version and test in a non-production environment before applying.

What changed recently?

Fault diagnosis on a Sophos device goes faster when you map the symptom to a recent change:

Did firmware update in the last 7 days?
Did the network (router, ISP, VPN) change?
Was the device moved physically?
Did paired devices (phone, hub, app) update?
Were any accessories swapped in or out?

The answer narrows the root cause to a manageable subset.

Before you start

A few things to confirm so the Sophos device fix goes cleanly:

Latest firmware downloaded if you're going to update.
Warranty + support contract status checked. opening sealed parts may void it.
Backup of current configuration (where applicable) taken.
Spare parts on hand if you anticipate replacement.
Adequate workspace, lighting, and time, rushing causes regressions.

How to confirm it's actually fixed

On a Sophos device, the test is rarely "reboot and see". Use this list:

Active reproduction: trigger the original failure path on purpose.
Indirect reproduction: do an activity that would expose the same subsystem.
Status indicator review: every LED / display / app status should be green.
24-hour soak: leave the device under normal load overnight; check the next morning.
Telemetry check: review the device or app's diagnostic log for new error entries.

Escalation guide

For a Sophos device, the right escalation depends on impact:

Cosmetic / minor: log a ticket via the Sophos app or web portal. Response 1-3 business days.
Mid-impact: phone support. Have your serial number ready.
Critical (production down, safety issue): in-person dealer / TAC visit. Bring proof of purchase.
Out of warranty: third-party repair shop with manufacturer-certified technicians.