Items Covered This Month Teac CTM-5928TXT TV Set. Teac CT-M488 TV set Sharp VC-H93X VCR Grundig GCF404/CUC2401 TV set

Mr Astor’s TV set looked almost brand new. It was a Teac CTM-5928TXT 63cm stereo set made in 1998 but it looked as though it had come straight out of the box.

The fault was no picture. The sound was OK and by turning up the screen control on the horizontal output transformer, there was a fully scanned raster with retrace lines. But there were no On Screen Displays (OSD) and the Teletext wasn’t working on Channel 7.

The first drama was getting a circuit diagram because, with about 20 ICs to deal with, I didn’t stand a chance without it. Eventually, a photocopy of the circuit arrived and I sat down with the CRO and coffee for a spell of signal tracing. My next problem was, as usual, access to the chassis. For some unknown reason, manufacturers are convinced they can save heaps of money by reducing the lengths of the cable so that it is almost impos-sible to reach the printed circuit side of the chassis without unplugging it.

My theory is that they save on the wire to buy more screws to fix the back on – why on earth do some sets need a dozen screws to keep it on while others use just two plastic clips? Nowadays things are so bad that it sometimes takes two seconds to fix the fault and three hours to fit the back on. (Well, OK, slight exaggeration..)

Anyway, I connected the CRO and followed the video from the detector, pin 17 of IC102 TDA8305A (TP102), through the sound trap and Q109 to IC303, TA8628N. From here, I followed the video from pin 9 IC303 to pin 17 IC305, TDA4565. And from pin 12, via R351, to pin 11 of IC304, TDA3504.

I was on familiar ground now; this IC often fails in other sets and the fact that I had tracked the signal this far was very encouraging. And as I had predicted, that was as far as the signal went. It should have come out on pins 1, 19 & 20, as red, green and blue signals to the picture tube socket, but there was no signal on any one of these pins.