Erratic output on Kenwood KR-A5030

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.

I don't know about the Kenwood, but it`s a common occurance on some lower end pro audio amplifiers and usually attributable to high resistance contacts on the speaker relay.

Ron

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?

-- David Farber David Farber's Service Center L.A., CA

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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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.

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.

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.

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

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

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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:

Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.