£20 on eBay for this nice 6.1 channel Yamaha amplifier. Rated at 0.02% THD+N at 100W output; 350W maximum output power across all channels. Despite the ".1", it doesn't actually have a built in subwoofer amplifier. It does have a line-level sub output. It also uses one less far-rear speaker, so it's only got 6 surround channels.
After I saw Dave Jones' (EEVblog) video on this amp, I had a look around eBay and saw there was a plentiful supply of this amplifier or its cousins going faulty on eBay. Picked one up for £20, plus another £10 got three half-decent speakers plus a subwoofer+amp (Combined unit; I'll post pictures of it in another thread.)
The fault is that the amplifier is completely dead or will only power up intermittently. And the cause? A single poly capacitor worth about £0.50. I just blasted this cap with a little freeze spray and it fired right up complete with functioning sound on the FM tuner.
This amplifier uses a rather novel, but somewhat complex energy saving standby circuit. It uses a real mains transformer, but switches it on and off a few times a second depending on load -- a sort of proto-switching power supply. It manages 0.2W standby power by doing that, whilst satisfying audiophiles (because it doesn't use a real switching power supply.)
The poly capacitor supplies the power to a D-type flip flop which latches the transformer on for a few cycles about three times a second using a FET and bridge rectifier. It also powers an optocoupler which tells the CPU if the AC line is present. When the poly cap falls in capacitance (typical failure mode due to self-healing from mains spikes), the voltage across the optocoupler drops, the signal goes away, and the CPU switches off the amp completely (no sign of life at all -- no standby light, no clicks from the relay...)
Now, this amplifier basically only fails in 230V markets. It's perfectly reliable when used on 115V (if it is rated for 115V of course.) Try and think why it might matter...
It's a Christmas present for my dad to accompany the 50" plasma (also one I repaired.)
After I saw Dave Jones' (EEVblog) video on this amp, I had a look around eBay and saw there was a plentiful supply of this amplifier or its cousins going faulty on eBay. Picked one up for £20, plus another £10 got three half-decent speakers plus a subwoofer+amp (Combined unit; I'll post pictures of it in another thread.)
The fault is that the amplifier is completely dead or will only power up intermittently. And the cause? A single poly capacitor worth about £0.50. I just blasted this cap with a little freeze spray and it fired right up complete with functioning sound on the FM tuner.
This amplifier uses a rather novel, but somewhat complex energy saving standby circuit. It uses a real mains transformer, but switches it on and off a few times a second depending on load -- a sort of proto-switching power supply. It manages 0.2W standby power by doing that, whilst satisfying audiophiles (because it doesn't use a real switching power supply.)
The poly capacitor supplies the power to a D-type flip flop which latches the transformer on for a few cycles about three times a second using a FET and bridge rectifier. It also powers an optocoupler which tells the CPU if the AC line is present. When the poly cap falls in capacitance (typical failure mode due to self-healing from mains spikes), the voltage across the optocoupler drops, the signal goes away, and the CPU switches off the amp completely (no sign of life at all -- no standby light, no clicks from the relay...)
Now, this amplifier basically only fails in 230V markets. It's perfectly reliable when used on 115V (if it is rated for 115V of course.) Try and think why it might matter...
It's a Christmas present for my dad to accompany the 50" plasma (also one I repaired.)
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