Re: Tektronix 2215, pulsing/chirping noise, no trace.


Most switching power supplies need a load on the output to be able to operate normally, so just as a reference by testing the pre-reg section with its output disconnected is most probably not a valid test. The full wave rectifier that you mention deals only with the mains AC input to convert it to DC for the operation of the switcher which then generates the +43V, so I doubt that the problem is there as it would rather blow the main fuse or would simply do nothing. But in any case have you checked the voltage across the (big) 75uF input capacitor? If for any reason that voltage is low or has a lot of ripple because that cap has aged and/or dried out I would think this might prevent the pre-reg from starting. On the output of the pre-reg there is only one rectifier diode that if I remember correctly is labeled CR907. Check that one as well, it might be leaky or open/shorted, and if in need of replacement has to be a high-speed fast recovery rectifier diode.

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