Static in right channel of Kenwood KA 7002 amp with volume off.

[FrankinAZ]

I'm an old guy, but I'm new here, so please excuse me if I don't do it right the first time.

There is an annoying static crackle sound coming out of the right channel on my Kenwood KA 7002.

No static in the left channel.

The static sound is independent of the volume setting and doesn't vary with the volume setting.

The static is loud enough to be annoying yet not so loud as to drive one from the room.

The static sound is there in the right channel independent of any settings of ANY of the knobs or switches, other than when the "null balance" button is held in, in which case the static is in both the right and left channels.

I've switched speakers and the static is only coming out of the right channel.

The static comes out of the right channel on headphones.

The static occurs with any, all or no sources plugged in.

All of the switches and dials have been cleaned and cleaned and cleaned.

The static currently starts 2 - 50 minutes after the unit is powered on and the static continues for as long as the amp is left on, but several times in the past there was no static for weeks and weeks ... until it returned a week or so ago.

Other than the annoying static ... all inputs, outputs, dials, switches and speakers seem to work correctly in both channels immediately upon powering on and as long as I leave it on.

One thing I noticed is that the transistors on the right side of the amp are running 10-20+ degrees cooler than the matching transistors on other side. Not sure if that indicates anything.

I'm familiar with basic minor electronic repairs but, so far, nothing much beyond using a volt-ohm meter and a soldering iron.

I like this amp but for me it's not worth $100+ to have it professionally diagnosed and repaired.

Thanks in advance for any help or advice.

 

[petehall347]

try with the normal separate switch on the rear panel in the separate position and see if it clears up .
it might even be this switch that is the problem .try what i said first then we can move on .

 

[nj pheonix]

I'm with Pete
Likely a dirty switch or control. If not possibly some component going out of spec or a noisy transistor.

 

[petehall347]

that switch will narrow down the problem somewhat .

 

[FrankinAZ]

that switch will narrow down the problem somewhat .

OK.
I'll check it first thing tomorrow morning and post the results.
Thanks.

 

[FrankinAZ]

try with the normal separate switch on the rear panel in the separate position and see if it clears up .
it might even be this switch that is the problem .try what i said first then we can move on .

The static disappears when the switch is in the "separate" position, but returns when the switch is in the "normal" position.

 

[petehall347]

ok its somewhere in the preamp section . corrosion on a switch etc . or maybe a faulty transistor

 

[FrankinAZ]

ok its somewhere in the preamp section . corrosion on a switch etc . or maybe a faulty transistor

Well, that narrows it down a bit.
I've cleaned the heck out of the switches so I'm going to (mistakenly?) assume the problem lies elsewhere.
My "research" indicates that the KA 7002 is chock full of
2sc458 transistors which are apparently infamous for becoming "noisy and opening and causing all sorts of pink noise and crackling".
Guess it's time to learn how to remove and replace transistors !
How hard can it be ?
: )

 

[petehall347]

its not that difficult once you can use a soldering iron .
just be sure to check pin-outs as they vary between different transistors .

 

[FrankinAZ]

its not that difficult once you can use a soldering iron .
just be sure to check pin-outs as they vary between different transistors .

So ... I have to check the pinout on the transistor I'm replacing as well as the pinout on the replacement in order to position the replacement correctly or ???

 

[petehall347]

yes you got it .
if your multimeter has a transistor tester you can check it with that .

 

[FrankinAZ]

Thanks to your help, it seems I've fixed my noisy KA 7002 by replacing the transistors in the low filter and high filter boards with 2sc2240s.
I first had to learn a bit about transistors, pin outs, base, emitter, collector, solder, soldering, cleaning/prepping the solder "gun", solder sucking, wire wraps, multimeters, DeoxIT, etc. etc.
I diagnosed with a hairdryer and freeze spray, starting large and narrowing down to the specific culprit.
I'm sure y'all would've gotten a laugh watching a person with zero experience, bare minimum knowledge, shaky hands and bad eyesight tackle my first electronics repair project.
In any case this first success(?) has given me the crazy idea that I might be able to see if I can get my Scott 342 StereoMaster thrift store find up and running, but that's another thread.