I've owned this HK730 since the late 80's it was my main unit through college but has since been relegated to a workshop system.
For the past 20+ years I've had an issue where the right channel won't produce any sound after it's been off for more than a few days. That is until I crank the volume up then it will come back on in a short static pop. Then I can turn the volume down and it works fine until I turn it off for a few days again. Years ago I discovered that I could turn off the speakers (deselect them) crank the volume for 2-3 seconds turn it back down and select the speakers again and all is fine.
I've gotten so used to it that I rarely think about it but was working on some other electronic projects and thought about it and decided to ask if anyone else had seen this before and if it's a quick fix. Years ago I looked for cold solder joints and used DeoxIT all of the switches/controls and the plugs between the boards. The only other thing I did, probably a decade ago, was to replace all of the lights with LEDs. Apart from the startup issue it sounds great and hasn't had any other symptoms.
Since it doesn't have to have a load when it's turned up I wasn't sure where to start looking.
For the past 20+ years I've had an issue where the right channel won't produce any sound after it's been off for more than a few days. That is until I crank the volume up then it will come back on in a short static pop. Then I can turn the volume down and it works fine until I turn it off for a few days again. Years ago I discovered that I could turn off the speakers (deselect them) crank the volume for 2-3 seconds turn it back down and select the speakers again and all is fine.
I've gotten so used to it that I rarely think about it but was working on some other electronic projects and thought about it and decided to ask if anyone else had seen this before and if it's a quick fix. Years ago I looked for cold solder joints and used DeoxIT all of the switches/controls and the plugs between the boards. The only other thing I did, probably a decade ago, was to replace all of the lights with LEDs. Apart from the startup issue it sounds great and hasn't had any other symptoms.
Since it doesn't have to have a load when it's turned up I wasn't sure where to start looking.
Do you have a scope? It would be the perfect tool for this problem.
Lacking a scope, you can improvise another audio amp and speaker to use as signal tracing tool. You can probably use the working channel as the signal tracer--- use a RCA cable to a line input as the probe, isolate the ground shell so that it can't cause inadvertent shorts. I'd add a 10K resistor and a 0.1uF cap in series to help protect the amp from damage.
In case it's not obvious, the idea is to catch the amp is its failed state. With a suitable test applied to the bad channel, probe along the signal path to find where the signal ceases in a divide and conquer search.
Good luck!
Lacking a scope, you can improvise another audio amp and speaker to use as signal tracing tool. You can probably use the working channel as the signal tracer--- use a RCA cable to a line input as the probe, isolate the ground shell so that it can't cause inadvertent shorts. I'd add a 10K resistor and a 0.1uF cap in series to help protect the amp from damage.
In case it's not obvious, the idea is to catch the amp is its failed state. With a suitable test applied to the bad channel, probe along the signal path to find where the signal ceases in a divide and conquer search.
Good luck!
It might be a rotten relay contact or so. In any case, whatever it may be, you will find it when you follow BSST's advice.
One of the transistors is doggy... or, a diode is failing. Usually, it is a transistor with very high gain... are there any Darlingtons in that amp??
Re diodes... usually, it is a 1N4148/1N914 signal diode that fails "just enough" to cause that behaviour... it becomes conductive when the superimposed audio signal is presented... which is what is happening in your case. Difficult to find... I used an oscilloscope to check for oscillations around these diodes.... the slightly off-the-spec ones will produce small amplitude, very fast oscillations, especially when presented with 1:1 probe capacitance. However, they will still measure okay with a diode tester !!!
Good luck.
Re diodes... usually, it is a 1N4148/1N914 signal diode that fails "just enough" to cause that behaviour... it becomes conductive when the superimposed audio signal is presented... which is what is happening in your case. Difficult to find... I used an oscilloscope to check for oscillations around these diodes.... the slightly off-the-spec ones will produce small amplitude, very fast oscillations, especially when presented with 1:1 probe capacitance. However, they will still measure okay with a diode tester !!!
Good luck.