[sdiy] The life and death of a Phonic power conditioner

Rutger Vlek rutgervlek at gmail.com
Sat Jan 28 12:30:10 CET 2017

Hi guys,

I'm having a bit of a struggle repairing my Phonic PPC9000E power conditioner. I found the service manual online (https://bmamps.com/Schematics/Phonic/Phonic_PPC_8000,_PPC_9000_Power_Distribution_Service_Manual.pdf). Originally, it's problem was that the led-bar indicating the line voltage was always maxed out. I tried calibrating it with the trimmers (SVR1 and SVR2), but all they do is affect the brightness, not the point at which the comparators switch. This led me to believe something is wrong with either the supply or the amplifier feeding the comparators. I measured too low a voltage between ground and the 15V line in the circuit (right after the regulator, over C4), so I was assuming the regulator to be broken. However... I thought, let's check if the recto before it is working correctly. I thought I'd be able to see this with my scope on the waveshape easily, and connected the scope's ground terminal to the circuits local ground (the negative side of C4) and boom! Big explosion! Fried part of my scope's ground clamp, fried C7 (even though it's rated 400V!) and made the fuse in the house switch off, as well as the ground leak detector. Big oops!

A little too late I realized the scope's ground is probably hard-wired to protective ground, rather than floating. Also... I was expecting this circuit to behave such that the local ground would adapt to any other ground applied to it. Wrong again! And finally.... why would a big (film, not elco!) cap get fried way below it's operating voltage of 400V. Or is that a DC voltage rating? And finally, why is my flu still not gone! (perhaps that explains it all...wait before repairs until you're recovered?)

If anyone has some insights that can help my slightly fuzzy flu-mind understand?


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