The Quick Answer
HP Smart Tank 7602 fax not working? A repair tech explains the VoIP line problem almost nobody diagnoses correctly, plus 4 other real fixes.
Fax feels like it should be the simplest function on a modern all-in-one — plug in a phone line, dial, done. When the HP Smart Tank 7602's fax function isn't working, failing to send, failing to receive, or reporting a communication error every single time, there's a good chance the actual culprit isn't the printer at all.
It's the phone line itself, and specifically what kind of phone line you actually have — which is a detail almost nobody thinks to check until every other fix has failed. For troubleshooting related components, consult HP DesignJet T.
Quick-Fix Summary
Fast version:
- Confirm you have a genuine dial tone on the exact line the fax is plugged into.
- Plug directly into the wall jack — no splitters, no answering machines in line.
- Check the fax header and settings for basic misconfiguration.
- Reduce the fax speed in settings if calls keep failing partway through.
- Identify whether you're on VoIP — my uncommon tip, and often the real root cause.
Fix 1: Confirm a Genuine Dial Tone
Unplug a standard telephone from the same wall jack and phone line the printer's fax port is connected to, and listen for a clear, standard dial tone.
Why this works: fax machines communicate using audio tones sent over what's supposed to be a clean analog phone connection, and if there's no dial tone, static, or an unusual sound on the line, the fax modem inside the printer has nothing reliable to work with — this rules the actual phone line in or out before you spend time on printer settings.
Fix 2: Remove Everything Else From the Line
Plug the printer's fax cable directly into the wall jack, with no splitters, surge protectors, answering machines, or other devices sharing that same line in between.
Why this works: every additional device on a phone line adds a small amount of electrical interference or signal loss, and fax communication is considerably more sensitive to line quality than a normal voice call — a splitter or an old answering machine that causes no noticeable problem for talking on the phone can be enough to corrupt the precise tones a fax handshake depends on.
Fix 3: Check Fax Header and Basic Settings
From the printer's control panel, find the Fax Setup menu and confirm your fax header information (your fax number and business name, if applicable) is entered correctly, and that the printer isn't set to answer on a ring count or ring pattern that doesn't match your actual phone service.
Why this works: a misconfigured header rarely blocks sending or receiving outright, but incorrect ring settings absolutely can — if the printer is waiting for a specific number of rings or a distinctive ring pattern that your line doesn't actually use, incoming faxes never get picked up at all, and it looks exactly like a broken fax function from the sending party's perspective.
Fix 4: Lower the Fax Speed
In the same Fax Setup menu, look for a Fax Speed setting, and if your faxes fail partway through or timeout on longer documents, try lowering it from the default fast setting to a slower, more conservative speed.
Why this works: fax communication negotiates a speed between the two machines at the start of every call, and a noisy or lower-quality line — which describes a meaningful share of phone connections today, even ones that sound fine for voice calls — can't reliably sustain a fast negotiated speed for an extended fax transmission. Dropping the speed setting trades a slightly longer transmission time for a connection that's far more likely to complete successfully.
Fix 5: Identify Whether You're on VoIP (My Uncommon Tip)
Here's the cause that explains more "fax just doesn't work" complaints on modern all-in-ones than anything else, and it has nothing to do with the printer's settings at all.
Ask yourself honestly: is your home or office phone service actually a traditional analog landline, or is it VoIP — meaning your "phone line" is really delivered through your internet router, a cable company's digital phone service, or a bundled service that converts your voice calls to data packets?
Most phone service today, including many services still called a "home phone line," is actually VoIP under the hood, even when it works perfectly for normal conversations.
This matters enormously for fax, because fax technology was built for real analog phone lines, and VoIP is fundamentally incompatible with it in a way that has nothing to do with call quality. Fax machines communicate using precise audio tones and timing that a genuine analog copper line carries faithfully.
VoIP services compress and digitize your voice for efficient transmission over the internet — a process that works beautifully for the human ear, which tolerates small distortions in speech without noticing, but that same compression scrambles the exact tones and timing a fax handshake depends on. The call can sound completely normal to a human listener and still be functionally useless for fax, because the compression is discarding exactly the information fax needs and voice doesn't.
To check: look at your bill or service description from your provider, or check whether your phone line runs through a cable modem, internet router, or a small adapter box rather than a traditional wall-mounted phone line junction.
If you're on VoIP, standard troubleshooting won't fix this — you need either a dedicated analog phone line for fax specifically (some providers still offer this), a fax-over-IP compatible service (a specific VoIP feature, not all providers support it, and it must be enabled correctly), or an internet-based fax service that bypasses phone lines entirely and works with your printer's scan-to-email or a fax app instead.
Why this works: once you understand that VoIP and fax are two technologies solving completely different problems — one optimized for human speech over data networks, the other for precise machine-to-machine tones over analog copper — the "my fax used to work and now it doesn't" pattern makes complete sense, because it usually lines up with when a household or office switched from a traditional landline to a bundled internet/phone package. This is the single most overlooked cause of fax failures on modern printers, precisely because the phone line appears to work perfectly for everything else you use it for.
When to Call a Professional
If you've confirmed a genuine analog dial tone, isolated the line from other devices, verified fax settings, tried a slower speed, and ruled out VoIP as the underlying cause — and fax still won't send or receive reliably — contact HP support with your printer's serial number, since a failing fax modem inside the unit becomes the more likely remaining explanation. If VoIP does turn out to be the cause, that's not a printer problem HP support can fix from their end;
the conversation instead belongs with your phone or internet provider about a fax-compatible line option.
