Re: Using a variac when testing always wise?
I used to find my Variac useful for old style transistor audio stuff. Saved blowing the new transistors if I failed to notice a blown resistor in the quiescent current setting circuit for example.
There was a Sony Trinitron TV which has an odd device in the PSU and line output stages (Silicon Controlled Switch?). When these blew, they took other stuff with them. There was a Sony bulletin on testing after repairs to ensure you’d caught all the faulty bits by powering the line oscillator from a DC supply (19V?), and slowly bringing the rest of the set, including the line output stage, on a Variac whilst watching various nodes with a ‘scope. From memory, on first applying power, the line oscillator supply set off towards full mains, and was only controlled when the oscillator started up and turned off the SCS. Shows the issues which might occur if powering an SMPS from a Variac.
Stuart
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