[TechAssist] Re: Audio..Kenwood KR-A56U..no audio output
- From: "Dave" <audioserviceclinic@xxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Fri, 7 Feb 2003 17:17:43 -0800
Sure! This procedure will be for discrete only. This is probably the most
common design now. Pretty much everyone has moved away from output ICs.
Just look at the emitter resistors for the output transistors. Most everyone
uses the dual cement resistors, about .22 ohms or close, depending on the
design. It has a three lead design with the center lead being the common
lead.
If you measure from that point to ground, at should not be more than about
20-30 milivolts. Ideally, 0 volts. Anything much more than that will trigger
the protection circuit. Past about 20 mils, that amp is considered to have
DC Offset(blown). Most of the new amps have no way to adjust this. It is
designed into the amp at this voltage. You used to be able to set the bias
and offset, but now-a-days, that is one extra part(cost) as well as one more
possible part that can change or deteriorate with age.
Now, here's the reason why you should get used to checking it there instead
of the output relay. Some manufactures, specifically, Harman Kardon, don't
use output relays. The protection circuit is completely different. DC offset
and high current/temp is sensed by a couple of transistors which change the
state of a pin on the micro. This change, signals the micro to shut down the
power control line to the power supply, which turns off the supply and
removes the offset condition, saving the load(speakers).
If you get used to checking it there, it doesn't matter whether the
protection is via relay or processor. In addition, that resistor is also the
point to measure bias on the amp, generally something you can adjust.
Getting around the protection can be difficult, but it is possible.
Dave
----- Original Message -----
From: "david stereo exchange" <stex@xxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Friday, February 07, 2003 16:52
Subject: [TechAssist] Re: Audio..Kenwood KR-A56U..no audio output
>
> Please tell me more....i am always looking for new ways to improve my
> Turn around time.!!!
> Thanks...
>
> david
> stereo exchange
> chicago, 1-773-784-0004
> http://www.turntablerepair.com/
>
>
>
> -----Original Message-----
> From: techassist-bounce@xxxxxxxxxxxxx
> [mailto:techassist-bounce@xxxxxxxxxxxxx]On Behalf Of Dave
> Sent: Friday, February 07, 2003 5:21 PM
> To: techassist@xxxxxxxxxxxxx
> Subject: [TechAssist] Re: Audio..Kenwood KR-A56U..no audio output
>
>
> That's one way. Make sure you're looking at the contacts and not the coil.
> It's not the best way if you want a full proof method that works every
time.
>
> Dave
>
> ----- Original Message -----
> From: "david stereo exchange" <stex@xxxxxxxxxxx>
> To: <techassist@xxxxxxxxxxxxx>
> Sent: Friday, February 07, 2003 15:05
> Subject: [TechAssist] Re: Audio..Kenwood KR-A56U..no audio output
>
>
> >
> > Take a look at the otherside of the relay and see if there is any dc
> > voltage...
> >
> > david
> > stereo exchange
> > chicago, 1-773-784-0004
> > http://www.turntablerepair.com/
> >
> >
> >
> > -----Original Message-----
> > From: techassist-bounce@xxxxxxxxxxxxx
> > [mailto:techassist-bounce@xxxxxxxxxxxxx]On Behalf Of Dave
> > Sent: Friday, February 07, 2003 4:39 PM
> > To: techassist@xxxxxxxxxxxxx
> > Subject: [TechAssist] Re: Audio..Kenwood KR-A56U..no audio output
> >
> > No! Don't short across the relay! If you have DC offset, you'll cook a
> > speaker!
> >
> > I can help you with that. I specialize in audio for the last 25+ years.
> > Maybe I missed your last reply. I asked if you have DC offset. Do you
know
> > how to measure it? I'll walk you through it.
> >
> > Dave
> >
> > ----- Original Message -----
> > From: "LeRoy Westlund" <llw@xxxxxxxxxx>
> > To: <techassist@xxxxxxxxxxxxx>
> > Sent: Thursday, February 06, 2003 21:57
> > Subject: [TechAssist] Re: Audio..Kenwood KR-A56U..no audio output
> >
> >
> > >
> > > Jeff,
> > > If it has +24 volt speaker relays,...try shorting across the contacts.
> > > It might have duel contacts and only one relay.
> > >
> > > LLW
> > >
> > > LeRoy Westlund
> > > Westlund TV & Electronics " Walk tall,...Walk straight
> > > 93 North Main and look the world
> > > Centerfield, UT 84622-0087 right in the eye "
> > > Ph./Fax 435-528-3822
> > > mailto:LLW@xxxxxxxxxx
> > >
> > > -----Original Message-----
> > > From: Jeff Dougherty <support@xxxxxxxxxxxxxxxxxx>
> > > To: Techsonline <techassist@xxxxxxxxxxxxx>
> > > Date: Thursday, February 06, 2003 2:45 PM
> > > Subject: [TechAssist] Audio..Kenwood KR-A56U..no audio output
> > >
> > >
> > > >
> > > >I don't do much audio equipment, so I hope someone can help me.
> > > >On the collector of each output, I have -/+50vdc, but no voltages on
> base
> > > or
> > > >emitter, the transistors test OK.
> > > >I tried tape and tuner functions and tape playback, no audio through
> > > speakers or
> > > >audio out jack.
> > > >Could the output transistors still be bad?
> > > >I found numerous bad connections, especially on Q32/33, with the
> > heatsink,
> > > but
> > > >repairing those didn't help. I do not have a schematic.
> > > >I'd appreciate any help...thank you.
> > > >
> > > >Jeff@xxxxxxxxxxxxxxxxxx
> > > >FAX 717-564-4952
> > > >Jeff Dougherty
> > > >Intrepid Video & Electronics Be careful of your thoughts.
> > > >501 Luther Rd They may become your words
> > > >Harrisburg, PA 17111 any moment.
> > > >717-909-8844
> > > >VCR tips, electronics info & general interest.
> > > >www.intrepid-video.com www.tech-repair.net
> > > >www.thetoolcaddy.com www.9-11-2001tragedy.com
> > >
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