Beovision MX 4000

23rd June 2013

All was not well in the line output stage of this set, the width was lacking and the set would revert to standby mode after a short period of operation. 3R13 (5.6k) on the tube base panel was found to be burned out and an attempt to operate the horizontal shift switch lead to arcing from inside the switch body. Of a few components which can be responsible for this fault, 4L4 (10mH) was found to have shorted turns, as indicated by a drastically reduced resistance of 3 ohms (around 40 ohms is the correct figure) and 4C105 (560nF) had a bulge in its side. Replacing 4C105, 4L4 and 3R13, as well as cleaning the switch, restored the width and allowed the set to operate normally. The failure of 4C105 probably instigated the fault, a 470nF capacitor was used in this position in some sets. Diodes 3D17 and 3D18 could also be damaged, depending on the position of the horizontal shift switch. [Beovision MX 4000]