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Windows Error 629 means the remote machine disconnected the dial-up port. In practice, the ISP’s access server or another remote Windows RAS server ended the call before the connection completed. That does not prove your modem has failed: a retired access number, account problem, PPP mismatch, noisy telephone path, or local modem configuration can all lead to the same remote disconnect. Microsoft’s definition is documented in its dial-up and VPN error-code table.
What Error 629 tells you
Error 629 is a connection-stage result, not a complete diagnosis. Your modem may dial and exchange carrier tones successfully, yet the remote server can terminate the session during PPP negotiation or authentication.
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Possible causes include an unavailable, overloaded, misconfigured, or retired access server; an incorrect number or username; a PPP or authentication mismatch; poor line quality; or modem firmware, driver, initialization, compression, or error-control incompatibility. The code itself does not identify which possibility occurred.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problems| Code | Microsoft’s meaning | First implication |
|---|---|---|
| 629 | The port was disconnected by the remote machine | Check the remote service, account, PPP negotiation, and line quality |
| 630 | The port was disconnected due to hardware failure | Investigate modem or local hardware |
| 651 | The modem or other connecting device reported an error | Check modem, driver, and cable |
| 676 | The line is busy | Wait or use another access number |
| 678 | There is no answer | Verify the number and service status |
| 679 | Carrier cannot be detected | Check the telephone path and modem |
| 691 | Access denied because the username or password is invalid on the domain | Verify account details and authorization |
| 797 | The modem was not found or was busy | Check detection, port selection, and modem state |
Use the complete Windows message, not only the number. Microsoft maintains the current code distinctions at the linked error-code page.
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Fastest checks before changing settings
- Record when it fails. Note whether the modem dialed, whether you heard a carrier handshake, and whether the call ended before or after a username/password prompt.
- Wait and redial once. Repeated calls will not fix a retired number or server outage and may trigger provider protections.
- Confirm a dial tone. Plug an ordinary telephone into the same jack and listen for severe hiss, hum, crackling, or intermittent drops.
- Verify the access number with the ISP. Confirm that it is active, supports analog modem access, is covered by your calling plan, and still permits your account.
- Try another published access number. A working second number strongly suggests a problem with the first server or route.
- Power-cycle the modem. Close the connection, disconnect power from an external modem, restart Windows, reconnect the telephone and serial/USB cables, then power the modem back on.
Check the telephone path
Dial-up needs an analog-compatible path. A dial tone alone is not proof that the service can carry modem signals. VoIP adapters, digital PBX extensions, cellular voice adapters, and managed phone systems can introduce compression, jitter, echo cancellation, or routing that breaks PPP negotiation.
- Test directly at the wall jack with a known-good telephone cable.
- Disconnect phones, fax machines, alarms, splitters, and other devices temporarily.
- On a PBX, include the required outside-line prefix (for example,
9where applicable) using the system’s dialing rules. - Test another jack or a conventional analog line if available.
- Ask the telephone provider for its documented call-waiting suppression prefix rather than assuming one universal code.
- If DSL service shares the wiring, bypass questionable filters or splitters for the test.
Verify that Windows sees the intended modem
- Open Device Manager (you can enter
devmgmt.msc). - Expand Modems and confirm the expected device appears without a warning icon.
- Open its properties and run the available diagnostic or query function. Driver versions expose different tabs, so the exact labels vary.
- Open the classic network-connections panel with
ncpa.cplwhere that applet exists, or use the Windows Settings interface on editions that redirect it. - Check that the dial-up profile selects this same modem rather than an old or disconnected device.
If a USB modem repeatedly disappears after sleep or hibernation, reconnecting it or restarting Windows may restore it. Continued disappearance indicates a driver, USB-port, power-management, or hardware issue, not merely a remote Error 629 condition. Microsoft documents a related resume problem for Error 633 at this support article.
Review or rebuild the dial-up profile
Check the existing profile
- Telephone number, area or outside-line prefix, and selected modem.
- Username format required by the provider, including any domain suffix.
- Password spelling, capitalization, and special characters.
- Single-link settings and the authentication methods required by the ISP.
- Unneeded protocols, compression, or legacy options that may interfere with negotiation.
Do not blindly enable unsecured authentication. Microsoft’s legacy guidance for authentication and multi-link negotiation concerns Error 734, not Error 629; see Microsoft’s Error 734 article. Use any weaker method only when the provider explicitly requires it, and only in a controlled legacy environment.
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Create a fresh connection
- Leave the old profile intact for reference or remove it if it is clearly obsolete.
- Create a new dial-up connection and select the detected modem.
- Enter the provider’s current number and exact credentials.
- Test the new profile before making further changes.
Use conservative modem compatibility tests
If the ISP or modem manufacturer supports it, temporarily test a lower connection speed, alternate hardware-flow-control setting, disabled compression, or disabled error control. These are diagnostic changes, not universal fixes. Use only an initialization string supplied for the exact modem model; random AT commands can stop the modem from dialing or reduce reliability.
Find the failing component with controlled substitutions
| Test | What it helps isolate |
|---|---|
| Same modem, different access number | One remote server or telephone route |
| Different modem, same line and number | The original modem or its driver |
| Same modem on another computer | Windows profile, driver, or serial/USB configuration |
| Same number from another telephone line | Your local line, PBX, VoIP adapter, or wiring |
| Different cable or wall jack | Physical telephone-path faults |
A substitution is most useful when you change one variable at a time. A successful alternate modem, line, or number is stronger evidence than repeatedly dialing the original setup.
When to contact the ISP or telephone provider
Contact the ISP when several local tests pass but the remote server still disconnects. Give support the access number, dates and times, whether carrier tone was heard, the modem make and model, Windows edition, tested alternatives, and any modem or Windows event-log entries.
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Ask whether the number is active, the account is enabled for dial-up, the server supports your authentication and PPP settings, and there is an outage, capacity problem, billing restriction, or changed username format. Contact the telephone provider if the line has no dial tone, audible noise, call-waiting interruptions, or an incompatible PBX/VoIP path.
When replacement hardware is justified
Replace the modem only after checking the number, line, profile, and drivers. Hardware becomes the leading suspect when Windows cannot detect it after port and driver checks, diagnostics fail, another modem works on the same computer and line, or you receive hardware-oriented codes such as 630, 651, or 666.
For a replacement, look for a documented external serial or USB modem, explicit support for your Windows edition, V.90/V.92 compatibility where the provider supports it, model-specific initialization documentation, and a return policy. Avoid fax-only devices and unbranded adapters without drivers. A new modem cannot fix an inactive ISP number, invalid account, incompatible phone service, or remote PPP configuration.
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Should you still buy dial-up service?
Availability is regional and can change. NetZero’s official page showed Basic Dial-Up at $11.95 per month and Accelerated Dial-Up at $16.95 per month when checked on August 16, 2026; first-month-free promotions, telephone toll charges, restrictions, availability limits, and paid support charges may apply. NetZero says an active home phone line or landline is required: netzero.net/dialup/. Its acceleration applies to certain web text and graphics, not every file transfer: NetZero’s explanation.
Juno’s official page displayed Unlimited Dial-Up at $15.95 per month with a first-month-free offer when checked; confirm local access numbers, restrictions, and phone charges before subscribing: juno.com/?tab=planspricing. EarthLink’s current page emphasizes fiber, wireless 5G/4G LTE, satellite, and other broadband categories rather than a current dial-up plan: earthlink.net/internet/.
For industrial, alarm, point-of-sale, or monitoring equipment, moving to cellular or IP service may require equipment, security, and contract changes; it is not automatically a drop-in replacement.
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What not to do
- Do not replace the modem immediately merely because Error 629 appeared.
- Do not disable every security setting or enable unsecured passwords without provider direction.
- Do not apply an AT command copied from a different modem model.
- Do not repair TCP/IP bindings as the first response; Microsoft associates that procedure with Error 720, documented at this support page.
- Do not assume a 56 Kbps connection; negotiated speed depends on the modem, line, network, server, and restrictions.
Frequently Asked Questions
Is Error 629 proof that my modem is bad?
No. Microsoft defines it as a remote-machine disconnect. A modem, driver, line, profile, or authentication problem can still cause the server to abandon the call, so test those variables before replacing hardware.
Can a VoIP line work with dial-up?
Sometimes, but a dial tone is not enough. Compression, jitter, echo cancellation, and modem handling can prevent PPP negotiation. A conventional analog line is the most useful comparison test.
Should I reinstall TCP/IP for Error 629?
Not as a first step. Microsoft documents TCP/IP binding repair for Error 720, a different error. Start with the access number, line, modem detection, credentials, and profile.
Why does another access number work?
That isolates the original number’s server, route, capacity, or configuration as the likely problem. Continue using the working number and report the failed one to the ISP.
What should I tell ISP support?
Provide Error 629, the number dialed, attempt times, whether carrier tone occurred, tested numbers or lines, modem model, Windows edition, credentials/profile changes, and any modem or event-log details.
Quick Recap
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