Erratic output on Kenwood KR-A5030

[Sam Goldwasser]

This receiver seems to work fine in every respect except that the volume
knob has to be turned up to a modest value before the speakers come on. This
will occur regardless of whether the speakers are actually enabled.

After that, it will usually run at any volume until power cycled

It has been sitting unused for about 10 years but don't know if this
was a problem back then.

Any common issues with this model?

Thanks.

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..

 

[Gareth Magennis]

This receiver seems to work fine in every respect except that the volume
knob has to be turned up to a modest value before the speakers come on.
This
will occur regardless of whether the speakers are actually enabled.

After that, it will usually run at any volume until power cycled

It has been sitting unused for about 10 years but don't know if this
was a problem back then.

Any common issues with this model?

Thanks.

Often this is down to dirty speaker relay contacts. If it has output
relays. Sometimes you can pop the top off them to spray the contacts,
others are sealed and need to be replaced.

Signal relays do much the same thing by the way.

If you see any relays inside, try getting it in the state where the speakers
aren't working and then start tapping them with a stick.



Gareth.

 

[Sam Goldwasser]

Often this is down to dirty speaker relay contacts. If it has output
relays. Sometimes you can pop the top off them to spray the contacts,
others are sealed and need to be replaced.

Signal relays do much the same thing by the way.

If you see any relays inside, try getting it in the state where the speakers
aren't working and then start tapping them with a stick.

Yeah, that's what I think also. I even seem to recall this very receiver
having that problem back before dinosaurs.....

There are two relays with covers that pop off.

Thanks!

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[David Farber]

Yeah, that's what I think also. I even seem to recall this very receiver
having that problem back before dinosaurs.....

There are two relays with covers that pop off.

Thanks!

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Power it up and don't turn up the volume. Put a scope probe at either the
speaker relay input or the emitter resistors of the power transistors. Turn
the volume up slowly. If you see signal before the sound comes on then you
know it's either the relay, or speaker switch. If you see signal at the same
time the sound comes on, then you have a different problem.

I'm a little confused by your observation that the problem happens whether
or not the speakers are enabled. How can you hear anything with the speakers
disabled? Are you using headphones? Or do you mean you turn the volume up
and down with the speakers off, then turn the speakers on, and then
everything is ok?

 

[Sam Goldwasser]

Power it up and don't turn up the volume. Put a scope probe at either the
speaker relay input or the emitter resistors of the power transistors. Turn
the volume up slowly. If you see signal before the sound comes on then you
know it's either the relay, or speaker switch. If you see signal at the same
time the sound comes on, then you have a different problem.

Intend to do something like that, or just clean the relay contacts!

I'm a little confused by your observation that the problem happens whether
or not the speakers are enabled. How can you hear anything with the speakers
disabled? Are you using headphones? Or do you mean you turn the volume up
and down with the speakers off, then turn the speakers on, and then
everything is ok?

Turn on and no sound. Turn off Speaker A switch. Turn up volume and turn
back down. Turn on Speaker A and it works at low volume.

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[David Farber]

Intend to do something like that, or just clean the relay contacts!


Turn on and no sound. Turn off Speaker A switch. Turn up volume and turn
back down. Turn on Speaker A and it works at low volume.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
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I remember the Kenwood KR-4070 had the power switch piggy backed onto the
speaker selector switch. If yours has the same design, make sure the long,
skinny, metal piece that connects the rotary switches together has not
slipped out of place. That might be contributing to the problem. This is
where hooking up your oscilloscope will answer your question in a matter of
seconds.

Good luck.

 

[Wiebe Cazemier]

I remember the Kenwood KR-4070 had the power switch piggy backed onto the
speaker selector switch. If yours has the same design, make sure the long,
skinny, metal piece that connects the rotary switches together has not
slipped out of place. That might be contributing to the problem. This is
where hooking up your oscilloscope will answer your question in a matter of
seconds.

Good luck.

I have a KR4070 here, and that is probably not the problem. That pin indeed
falls out sometimes, but it just results in not being able to turn the
speakers on; or the entire amplifier for that matter.

BTW I find it rather strange that dirty relay contacts would cause this
behavior, most notably because after the sound has kicked in, the low volume
setting works again, and because turning up the volume with the speakers
disabled, also turns them on.

If your relay experiment fails, try locating the power amplifier section and
determine if the problem is present on the input signal, or only on the power
output.

 

[Mark D. Zacharias]

Intend to do something like that, or just clean the relay contacts!


Turn on and no sound. Turn off Speaker A switch. Turn up volume and turn
back down. Turn on Speaker A and it works at low volume.

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Just sounds like flaky relay contacts to me. Put a load on it look at a sine
wave output on a 'scope, and tap on the relay(s). Probably see one or more
of them cut out - could be solder connections there at the relay as well.

To David Farber:
This model isn't even CLOSE to the old KR-4070... that was an analog 40 w/ch
receiver from the '70s. This is a more modern surround receiver.

Mark Z.

 

[Gareth Magennis]

I have a KR4070 here, and that is probably not the problem. That pin
indeed
falls out sometimes, but it just results in not being able to turn the
speakers on; or the entire amplifier for that matter.

BTW I find it rather strange that dirty relay contacts would cause this
behavior, most notably because after the sound has kicked in, the low
volume
setting works again, and because turning up the volume with the speakers
disabled, also turns them on.

You may well find it strange, but that is in fact exactly what happens in
the real world. Last time I heard any kind of technical explanation, it
seemed to be little understood and/or quite a complex situation - often a
kind of diode junction is formed. Turning up the volume (voltage across the
junction) often seems to "punch through" the dirt and it will then behave
normally for a while. You could try Googling for technical information on
this. I did for about a minute and gave up.



Gareth.

 

[Sam Goldwasser]

I remember the Kenwood KR-4070 had the power switch piggy backed onto the
speaker selector switch. If yours has the same design, make sure the long,
skinny, metal piece that connects the rotary switches together has not
slipped out of place. That might be contributing to the problem. This is

No, here there are separate pushbuttons for Spkr A and Spkr B.

where hooking up your oscilloscope will answer your question in a matter of
seconds.

I know. I'm lazy. Also, getting to the solder side of the PCB
looks like a major disassembly.

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[Sam Goldwasser]

This is a final report on this problem.

I believe it was actually the solder connections to the PCB and not the
relay contacts themselves.

Kenwood actually provided easy acces to the bottom of the PCB. A large
square section was partially punched out with only 4 thin metal strips
holding it in place. So, cutting two on one side allowed the relevant
part of the botton plate to be swung out of the way exposing everything
but the AC line circuitry.

When duplicating the erratic behavior, gently touching one of the relay
pins would make the sound come and go. While there was no visible crack,
the relay's solder terminals are physically the stationary
contacts. So, the constant pounding over the years must have loosened
at least one of them just enough to make marginal contact with the solder
on this single-sided PCB.

I removed the relay entirely and inspected the interior. The contact points
were in perfect condition with no sign of wear or burning.

After reinstalling the relay, the receiver has been 100 percent reliable.

Thanks to all who replied.

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[gareth magennis]

This is a final report on this problem.

I believe it was actually the solder connections to the PCB and not the
relay contacts themselves.

Kenwood actually provided easy acces to the bottom of the PCB. A large
square section was partially punched out with only 4 thin metal strips
holding it in place. So, cutting two on one side allowed the relevant
part of the botton plate to be swung out of the way exposing everything
but the AC line circuitry.

When duplicating the erratic behavior, gently touching one of the relay
pins would make the sound come and go. While there was no visible crack,
the relay's solder terminals are physically the stationary
contacts. So, the constant pounding over the years must have loosened
at least one of them just enough to make marginal contact with the solder
on this single-sided PCB.

I removed the relay entirely and inspected the interior. The contact
points
were in perfect condition with no sign of wear or burning.

After reinstalling the relay, the receiver has been 100 percent reliable.

Thanks to all who replied.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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Important: Anything sent to the email address in the message header above
is
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in the
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