HP M1522nf Service Manual - Page 83

If you experience problems using the fax feature on a VoIP network, ensure that all of the product cables and settings are correct. Configuring the Fax Speed setting to Medium(V.17) or Slow(V.29) can also improve your ability to send a fax over a VoIP network. If you continue to have problems faxing, contact your VoIP provider. The fax subsystem The formatter, fax card, firmware, and software all contribute to the fax functionality. The designs of the formatter and fax card, along with parameters in the firmware, determine the majority of the regulatory requirements for telephony on the product. The fax subsystem is designed to support V.34 fax transmission, lower speeds (such as V.17 fax), and older fax machines. Fax card in the fax subsystem Two versions of the fax card are used in the HP LaserJet M1522 MFP. One is used in the North American, South American, and Asian countries/regions. The other is used primarily in European countries/regions. The fax card contains the modem chipset (DSP and CODEC) that controls the basic fax functions of tone generation and detection, along with channel control for fax transmissions. The CODEC and its associated circuitry act as the third-generation silicon DAA to achieve compliance world-wide regulatory requirements. European products must use the fax cord that is included in the product box. North American and Asian products should be compatable with any phone cord, although users who experience fax errors should try the included fax cord. Safety isolation The most important function of the fax card is the safety isolation between the high-voltage, transientprone environment of the telephone network (TNV [telephone network voltage]) and the low-voltage analog and digital circuitry of the formatter (SELV [secondary extra-low voltage]). This safety isolation provides both customer safety and product reliability in the telecom environment. Any signals that cross the isolation barrier do so magnetically. The breakdown voltage rating of barriercritical components is greater than 5 kV. Safety-protection circuitry In addition to the safety barrier, the fax card protects against over-voltage and over-current events. Telephone over-voltage events can be either differential mode or common mode. The event can be transient in nature (a lightning-induced surge or ESD) or continuous (a power line crossed with a phone line). The fax card protection circuitry provides margin against combinations of over-voltage and overcurrent events. Common mode protection is provided by the selection of high-voltage-barrier critical components (transformer and relay). The safety barrier of the fax card PCB traces and the clearance between the fax card and surrounding components also contribute to common mode protection. A voltage suppressor (a crowbar-type SIDACTOR) provides differential protection. This device becomes low impedance at approximately 300 V differential, and crowbars to a low voltage. A series thermal switch works in conjunction with the crowbar for continuous telephone line events, such as crossed power lines. ENWW Fax functions and operation (fax models only) 65