Technology of Q 2500 colour TV set

Technology of Q 2500 colour TV setOn start-up C 479/22 µF is very quicklycharged up by R 471/22 k. For C 489/22 µFcharging occurs more slowly via R 477/10 kand R 4476/33 k. This means that in thecharging phase pin 9 is more positive withrespect to pin 10. On shut down C 489 dischargesrapidly via D 474 (which releases R476) and R 477. Pin 9 is again more positivewith respect to pin 10 and mute is implementedagain internally.TDA 7296 can be considered to be an operationalamplifier. It is controlled by its noninvertinginput pin 3. The amplification is calculatedfrom the negative feedback combinationR 478/473.This results inR 478 22 kV = 1 + --------- = 1 + -------- = 33R 473 0.68 kThe amplified signal is felt on pin 14 and forthe left channel is fed to the loudspeakers viaL 479.The R 479/C 471 combination is necessary foran internal bootstrap. In addition, the outputphase is equipped with an overload and temperatureprotection circuit.The two output stages are supplied with voltagesymmetrically. It is taken from the transformerat zero potential and rectified andsmoothed by D 686/687 and C 687. With thehelp of the R/C combination 466 and 468 it issplit into +/- 18 V (see also power supply).This measure achieves a halving of the peakcurrent by the rectifier diodes D 686/687 and ahigher undistorted output performance, especiallyfor low frequencies.An output stage without any electrolytic capacitorscontributes to this.Document Q 2500 43 © Loewe ProCollege