QRX-949a clicking in and out of protection when turned up

jberger

AK Subscriber
Subscriber
I was testing out a QRX-949a yesterday (boy, did it sound nice).

However, when I got above approximately 1/2 watt of output, the unit started clicking in and out of operation rapidly; I'm assuming that it's the protection circuits. Turning down the volume stopped the clicking and returned to functioning.

The events occurred even if the speakers (Andrew Jones Pioneer's) were disconnected, or if 8 ohm 100w resistors were in place, and occurs whether the receiver has the back power connector set to 2 channel or 4 channel mode.

Suggestions on where to look next? I have not yet checked bias or DC offset.
 
try with no load .
try with no inputs .
try with shorted inputs .

not necessarily in that order .. 2 or more can be tried at the same time .

before trying anything deoxit all controls .
 
Same problem with no load, as long as there is signal.
No input signal, and it's fine all the way up.
Have not tried shorted inputs, but problem also shows up with tuner as source.
Adjusting the gain of the input source (signal generator or phone) recreates the problem, as long as the master volume is high enough.
Power meters show this happening under 1 watt.
Problem occurs on both channels simultaneously, and is accompanied by a relay clicking. Minimal delay clicking back on by lowering the volume and the sound returns.
Flaky relay? DC offset and bias? Power supply?
 
Checking dc and bias is a good start.
The QX-949a makes extensive use of small blue Sanyo caps. Over time they start to behave less and less as capacitor, but more as a resistor. It is wise (or should I say necessary) to replace these. They are probably the source of your problem.
 
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