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Weird problem with vintage Kenwood KA-8100 integrated amp

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  • Kenwood
  • Audio
Last response: in Home Audio
March 16, 2005 10:21:24 PM

Archived from groups: rec.audio.tech (More info?)

I just picked up a vintage Kenwood KA-8100 integrated amp (circa late
70's) in really good condition. It has an intermittent problem where
the right channel will sometimes completely drop out, but then I am
able to get it back by turning the volume up and at some point the
right channel will kick in and be fine again. It happens very
sporadically and sometimes not do it for a day or more. Except for
this little quirk, the amp works and sounds great.

Any ideas on what might be wrong?

TIA!
Bob

More about : weird problem vintage kenwood 8100 integrated amp

Anonymous
March 16, 2005 11:09:35 PM

Archived from groups: rec.audio.tech (More info?)

In article <d1a0vk$q30$1@reader1.panix.com>,
Bob <am_dew@REMOVepanixThis.com> wrote:

>I just picked up a vintage Kenwood KA-8100 integrated amp (circa late
>70's) in really good condition. It has an intermittent problem where
>the right channel will sometimes completely drop out, but then I am
>able to get it back by turning the volume up and at some point the
>right channel will kick in and be fine again. It happens very
>sporadically and sometimes not do it for a day or more. Except for
>this little quirk, the amp works and sounds great.
>
>Any ideas on what might be wrong?

The four things I'd look for, roughly in order:

- A speaker-protection relay whose contacts have gotten dirty,
oxidized, or burned. It's not uncommon for manufacturers to use
relay which are not "self-wiping", and any crud which builds up on
the contacts, stays there. This sort of problem can be fixed by
either replacing the relay, or opening it up (if necessary) and
using a contact burnisher to clean the contact surfaces.

- An electrolytic coupling capacitor, located between two of the
amp's stages, which has dried out or leaked and has become
intermittent.

- A bad (cracked?) solder joint on the PC board, most probably at or
near one of the output transistors. Tapping on the board and
components with the eraser end of a pencil could locate the bad
joint pretty quickly.

- A bad volume control.

Shouldn't be hard to locate this problem with a signal injector and
signal tracer.

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Anonymous
March 16, 2005 11:48:58 PM

Archived from groups: rec.audio.tech (More info?)

Controls need cleaning. In this case, the pushbutton controls.

Mark Z.


"Dave Platt" <dplatt@radagast.org> wrote in message
news:113h4jv76dq5o13@corp.supernews.com...
> In article <d1a0vk$q30$1@reader1.panix.com>,
> Bob <am_dew@REMOVepanixThis.com> wrote:
>
>>I just picked up a vintage Kenwood KA-8100 integrated amp (circa late
>>70's) in really good condition. It has an intermittent problem where
>>the right channel will sometimes completely drop out, but then I am
>>able to get it back by turning the volume up and at some point the
>>right channel will kick in and be fine again. It happens very
>>sporadically and sometimes not do it for a day or more. Except for
>>this little quirk, the amp works and sounds great.
>>
>>Any ideas on what might be wrong?
>
> The four things I'd look for, roughly in order:
>
> - A speaker-protection relay whose contacts have gotten dirty,
> oxidized, or burned. It's not uncommon for manufacturers to use
> relay which are not "self-wiping", and any crud which builds up on
> the contacts, stays there. This sort of problem can be fixed by
> either replacing the relay, or opening it up (if necessary) and
> using a contact burnisher to clean the contact surfaces.
>
> - An electrolytic coupling capacitor, located between two of the
> amp's stages, which has dried out or leaked and has become
> intermittent.
>
> - A bad (cracked?) solder joint on the PC board, most probably at or
> near one of the output transistors. Tapping on the board and
> components with the eraser end of a pencil could locate the bad
> joint pretty quickly.
>
> - A bad volume control.
>
> Shouldn't be hard to locate this problem with a signal injector and
> signal tracer.
>
> --
> Dave Platt <dplatt@radagast.org> AE6EO
> Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
> I do _not_ wish to receive unsolicited commercial email, and I will
> boycott any company which has the gall to send me such ads!
Related resources
December 18, 2008 7:50:57 PM

i have had this problem with my ka 8100 since i purchased it new in 1978. it was shipped back to three different kenwwod service centers . they replaced the filter buttons which worked for a while but i soon had to resort to working the buttons untill both channels worked . kenwood claimed the problem was hard to find because it was intermitant.i have never bought another kenwood product since. a great sounding unit no doubt when it works..as last resort try some contact cleaner on the buttons and work the **** out of them.. unit off of course
Anonymous
February 25, 2009 10:49:10 PM

Got my KA8100 for free from a friend just becos of mentioned issue...

When one channel dropp'd you could do several things to get it back:
- raising volume drastically
- push filter buttons
- switch between Hz on the bass/treble ctrls
- very quickly turn off/on/off/on

In fact, almost "whatever" pushing/bending helped...

After some brainstorming... I did attack the speaker protection relay. For a start I cleaned the connectors and the problem disappeared for 1-2 months. Then I understood that the relay needed some more, so I did clean it once more but I then adjusted it somewhat so that the movement pushed a little more -case closed, it has worked perfect for a few years by now.

As an old DJ (70's - 80's) I do HATE those relays and protective circuits... too many times I lost sound in spite of working speakers and amps but non-working relays/circuits. My own equipment was modifyed from start (hardcore -no protection or unnessesary components) but I always had to carry spare power amps when dj:ing on other eqipment.