Fixing Up The Sony 5-303

[compucat]

A while back my little Sony broke down and I am now just getting the bug to fix it. The picture shrank on all sides and after a while the raster faded completely. The sound and tuning are ok. At first I thought the power supply was at fault. I narrowed the trouble to the sweep board.

The 300v boost supply is absent. A quick and intersting way to confirm this is look at the channel indicator light. It is a neon bulb powered from the boost voltage supply. Mine went out with the raster. After replacing caps and checking resistors, no improvement. I proceded to measure voltages in the horizontal sweep circuits. The 12.5v B+ voltage is showing up everywhere it should but there is no voltage at the base of the horizontal output transistor. Working backward from there, I narrowed it down to the horizontal oscillator transistor. Removing it from the circuit, I discovered an open between the base and emitter. It is a 2SC140. I have a junker sweep board from which I'll snag a replacement transistor and see what happens then.

This is turning out to be an interesting troubleshooting excercise, especially since the TV was previously working. After I get it going again, I'll finish recapping the sweep board. Also, I ordered a N.O.S. picture tube for it. The original was looking a little soft when it last worked.

I'll keep posting my progress for anyone who might be interested.