A Lesson In ‘Fast Recovery’

Submitted by Member: Steve Webb

In the mid 70’s the Thorn 9000 had just appeared with it’s revolutionary new cyclops power supply where all the various supply rails were derived from the combined chopper/line timebase. Chassis was bristling with fast recovery diodes and in the faulty receiver to which I had been called, one of the supply diodes had gone ‘short circuit’.

Being a new receiver and chassis to us, I didn’t have a diode of the type required in my field kit. So resourcefulness kicked in or so I thought and I fitted a BY127. The set burst into life, but minutes later the set died again with smoke issuing forth as my newly fitted diode failed. So it was back to base for the correct fast recovery diode, which is what I should have done In the first place!.

Significantly I remembered the guy who conducted the training course for the 9000 at the training school telling us ‘The days of fitting a BY127 standard recovery diode everywhere are over’ My experience with my first Thorn 9000 fault certainly endorsed that.

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Nuvistor
Member
2 years ago

My first dealing with a failed fast recovery diode was in a BW small screen portable set, probably 12 inch screen. I think it was a Toshiba but could be wrong. The diode was OC, it was in the line timebase, I tried a 1N54xx diode, the set came to life no other problems but the diode got very hot. At least the fault had been proved so the correct diode had to be ordered along with a few for spares.

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