LOPT / FBT Tester


Posted on Oct 24, 2012

This little instrument identifies faults in horizontal output stages by doing a `ring` test, i.e. it applies pulses to the LOPT / FBT primary circuit, and counts the number of damped oscillations or `rings` produced. For each `ring` down to about 15% of the test pulse amplitude, one LED in the `bargraph` lights up... nearly all faults will greatly reduce the number of `rings` and give a very low reading.



It can be used on both monitors and TVs because it`s not frequency-sensitive, and the test signal amplitude is only 650mV- low enough not to forward-bias semiconductors in the circuit. To do a basic test, you connect the test leads between chassis




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