PHILIPS 320 CHASSIS
I’d appreciate any guidance on tackling a “no results” fault
on one of these sets. There’s no sound or raster.
This solid-state chassis uses a thyristor to produce a
stabilised 163V supply at TP15. The thyristor regulator
circuit is preceded by a bridge rectifier, and if this is in order
you should record 210V at its output. The most common
cause of the fault however is failure of the thyristor or an
associated component. If the thyristor is defective, replace it
with a BT100A/02, which is more reliable than the original
BT100A/500R. Apart from the thyristor and fuses, suspect
components include the 10S2 surge limiter resistor R4639,
the series choke L4635, and the thermal cutout R4465 if
fitted. A dry -joint on the trigger pulse coupling capacitor
C5624 is another cause of no h.t. sometimes encountered.
Once you’ve restored the h.t. supply, set it to 158V for
increased reliability – adjust with R5630. If this results in
slight lack of width, connect the link across the width choke
L2442 in the line output stage. A point to note when dealing
with these sets is that the chassis is live.