Sony TC-WR720A Service Manual - Page 2

TC-WR720/WR720A FEATURES • The Dolby HX PRO* system which improves the linearity of a tape's high-range response during recording. • A relay function for long recording and playback. • Automatic tape type detection during playback and recording. • Auto-synchro dubbing at normal or high (double) speed. • AMS and memory play functions which provide easy access to desired selections. • An easy-to-read digital counter which shows the elapsed recording or playback time for decks A and B. * Dolby noise reduction and HX Pro headroom extension manufactured under license from Dolby Laboratories Licensing Corporation. HX Pro originated by Bang & Olufsen. "DOLBY' , the double-D symbol DO and - HX PRO- are trademarks of Dolby Laboratories Licensing Corporation. SAFETY-RELATED COMPONENT WARNING!! COMPONENTS IDENTIFIED BY MARK A OR DOTTED LINE WITH MARK A ON THE SCHEMATIC DIAGRAMS AND IN THE PARTS LIST ARE CRITICAL TO SAFE OPERATION. REPLACE THESE COMPONENTS WITH SONY PARTS WHOSE PART NUMBERS APPEAR AS SHOWN IN THIS MANUAL OR IN SUPPLEMENTS PUBLISHED BY SONY. ATTENTION AU COMPOSANT AVANT RAPPORT A LA SECURITE! LES COMPOSANTS IDENTIFIES PAR UNE MARQUE A SUR LES DIAGRAMMES SCHEMATIQUES ET LA LISTE DES PIECES SONT CRITIQUES POUR LA SECURITE DE FONCTIONNEMENT. NE REMPLACER CES COMPOSANTS QUE PAR DES PIECES SONY DONT LES NUMEROS SONT DONNES DANS CE MANUEL OU DANS LES SUPPLEMENTS PUBLIES PAR SONY. SAFETY CHECK-OUT After correcting the original service problem, perform the following safety check before releasing the set to the customer: Check the antenna terminals, metal trim, "metallized" knobs, screws, and all other exposed metal parts for AC leakage. Check leakage as described below. LEAKAGE TEST The AC leakage from any exposed metal part to earth ground and from all exposed metal parts to any exposed metal part having a return to chassis, must not exceed 0.5 mA (500 microampers). Leakage current can be measured by any one of three methods. I. A commercial leakage tester, such as the Simpson 229 or RCA WT-540A. Follow the manufacturers' instructions to use these instruments. A battery-operated AC milliammeter. The Data Precision 245 digital multimeter is suitable for this job. 3. Measuring the voltage drop across a resistor by means of a VOM or battery-operated AC voltmeter. The "limit" indication is 0.75 V, so analog meters must have an accurate lowvoltage scale. The Simpson 250 and Sanwa SH-63Trd are examples of a passive VOM that is suitable. Nearly all battery operated digital multimeters that have a 2V AC range are suitable. (See Fig. A) To Exposed Metal Parts on Set 0.15µF 1.5kf2 AC voltmeter (0.751/1 = Earth Ground Fig. A. Using an AC voltmeter to check AC leakage.