Re: Yamaha R-50 receiver failed

Mark D. Zacharias wrote:

Jamie wrote:
<snip>

you most likely have bad Caps in the power supply..
a lot of receivers have power supplies that
sample the voltage at the main caps while they
are being charged via a resistor to allow for slow
start up to avoid inrush currents.
when the desired charge is reached, a relay will
bridge this trickle charging system to allow full power
and also start the receiver.
since your fuse was blown, it's possible (theory only) that
one of your caps or even a bridge rectifier has shorted and
is not allowing for the voltage to reach its peak, which btw
must be the reason why you didn't blow out the new fuse you put in ?
if this is the case, you should have a high wattage resistor getting
vary hot!, or maybe by this time has opened or unsoldered it self from
the board ?


Half-baked gobbledygook.

1. A shorted rectifier or main filter cap would blow the fuse every time, not just the first time.
2. The receiver in question has a DC and current detect circuit, not a simple R/C delay for the relay.
never said it was a simple RC circuit, i think i said something on the
effects of sampling the voltage?, this implies its looking for a desired
level. and many upper end units use separate source from the main bridge
and caps to operate this little circuit!. it is very possible for a
bridge or cap to have a short with the trickle charge R being on the AC
side of the transformer into the bridge. this would protect the fuse from being blown out again since the monitoring of voltage never reaches
its level via the low current charge Network that is being used.
if problems arise while in operation then it would make sense for the
fuse to be defective since the PSU would have this low current R bypassed and over current would have been seen..
defects could also lead to Audio output being shorted which i also connected to the supply during charge up. this form of protection is able
to monitor both PSU and attached devices.
so it's very common to find fuses blown during operation and not blow
after you replace them,. this generally means the PSU has not met its desired peak level of charge before the by pass contactors/electronic switch are connected.




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