Beovision 3802 (20AX chassis)

29th August 2008

This set suffered from annoying intermittent width variations, mainly in the corners of the picture. The first suspect was of course the EW transformer 6T3 but as the new type was fitted this clearly was not the case on this occasion. The EW modulator diodes 6D4 and 6D5 were tried, along with the EW driver transistor 6TR6 but the symptoms returned after a few hours use. The line scan coil plug P13 was found to be in poor condition so the wires were removed and soldered directly to the underside of the pins, this helped but the fault was still not completely cleared. Eventually it was discovered that the plug on the frame timebase module (P19) was making poor contact at pin 8, the field scan current return path. The plastic body of the socket was melted, showing that a high resistance connection had been getting hot. As the EW circuit takes its frame drive waveform from this point this explains why the geometry was affected. Removing the plug and wiring the module in directly finally resulted in stable operation. [Beovision 3802]