Got another amp to repair... this beautiful Yamaha 7.1ch HDMI amp is eating mains fuses for breakfast. Cost approx £27 including delivery, cheaper than my old RX-V465DAB!
Will turn on & work briefly (VFD lights up and shows "Main Zone"), but no audio, buzzing from transformer and pop goes the fuse!
Checked the outputs of the transformer and can't find any -obvious- shorts. I hook lightbulb in place of fuse & put the scope across the output of one of the taps and I can see the positive section of the wave is very stunted... the negative section looks OK. Amp just clicks on and off rapidly with lightbulb due to reduced power.
I suspect though have not yet confirmed that the bridge rectifier has one or two failed diodes internally. All O/P transistors tested OK, but since the short shows on the transformer as being asymmetric I believe that it is probably a short that is hiding behind a diode (shorted output stage would lead to both halves of wave being equally stunted.)
I'm going to try with my variac later.
Will turn on & work briefly (VFD lights up and shows "Main Zone"), but no audio, buzzing from transformer and pop goes the fuse!
Checked the outputs of the transformer and can't find any -obvious- shorts. I hook lightbulb in place of fuse & put the scope across the output of one of the taps and I can see the positive section of the wave is very stunted... the negative section looks OK. Amp just clicks on and off rapidly with lightbulb due to reduced power.
I suspect though have not yet confirmed that the bridge rectifier has one or two failed diodes internally. All O/P transistors tested OK, but since the short shows on the transformer as being asymmetric I believe that it is probably a short that is hiding behind a diode (shorted output stage would lead to both halves of wave being equally stunted.)
I'm going to try with my variac later.
Comment