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Kenwood KA-8300 has no output.

todd.brust

todd.brust

New Member
Hello all!

It has been a while since I lurked around here, but I am back with a little project.

A buddy of mine picked up a Kenwood KA-8300 integrated receiver, and it has no output. Lights come on and whatnot, but never had any audio pass through, or see any meters. I thought it might be something easy like a bad relay, but that is not the case.

I was able to download the service manual for the unit, and did some troubleshooting down to some specific components on the amplifier boards, however I checked, replaced bad components, and still have no output. It did say to check the TA-100W amplifier chips, but I honestly do not know how to go about even checking those. My component level troubleshooting skills have been non existent, but I am trying to fix that.

If anyone has had some experience repairing these, I would be very interested in any insight and or tips to get through this beast. Thanks for any and all help in advance!

MODS: If this is against the rules for this section of the Forum, please delete and I can re-post where appropriate, but this looked to be the ideal spot.
 
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Might be better in the Kenwood forum.

I'm not familiar with that amp, but I've been around STKs enough to know they usually short rather than go open, in which case a fuse blows.

First and most important, is the tape monitor switch in tape or source position? If it's in tape, you won't have any signal unless you have something plugged into the tape "play" input for that selection. Very common error. And the switches can get tarnished and quit working when someone "tests" them.

Second thing to do is check the voltages on the main filter caps. Quite possible a fuse is blown and you have lights but no amplifier.

Make or buy a Dim Bulb Tester - a tungsten filament incandescent bulb in series with the hot side of the power cord. This will give you a visual indication of current draw AND prevent a short from burning anything else up.
 
You can do a quick check of the TA100 power pacs
Carefully test with a voltmeter on each IC
Pin 2 of each IC should show about +50vdc
Pin 6 of each IC should show around -50vdc

Then check pin 5 of each IC. If you show anything above 20mv dc, the IC is bad and preventing the protect circuit from energizing the relay. Ususally when the IC's go bad they short, resulting in high DC on pin 5 which is the output.
 
Tom B said:
Carefully test with a voltmeter on each IC
Click to expand...

I use some heat shrink on my DVM + probe so only the tip is exposed. I use a banana to mini grabber on the - probe (and clip it to the chassis).
 
HPMguy said:
Might be better in the Kenwood forum.

I'm not familiar with that amp, but I've been around STKs enough to know they usually short rather than go open, in which case a fuse blows.

First and most important, is the tape monitor switch in tape or source position? If it's in tape, you won't have any signal unless you have something plugged into the tape "play" input for that selection. Very common error. And the switches can get tarnished and quit working when someone "tests" them.

Second thing to do is check the voltages on the main filter caps. Quite possible a fuse is blown and you have lights but no amplifier.

Make or buy a Dim Bulb Tester - a tungsten filament incandescent bulb in series with the hot side of the power cord. This will give you a visual indication of current draw AND prevent a short from burning anything else up.
Click to expand...


I haven't tried those switches yet, but I am still never hearing the speaker relay click on. The main fuse is good and I am getting rail volatge at the power supply outputs, so I dont think anything is shorted. I have some plans for a dim bulb tester, but just haven't gotten around to it yet.
 
Check offset voltage (center of the STK emitter resistors, should be very close to zero. I've seen a bad voltage amp (differential pair(s) and current mirror) cause enough offset to keep the protection relay open.

What I usually do in a case like this is get the schematic out and start checking voltages, where they differ markedly from the schematic there is a bad part somewhere close.
 
rickl said:
I use some heat shrink on my DVM + probe so only the tip is exposed. I use a banana to mini grabber on the - probe (and clip it to the chassis).
Click to expand...
Tom B said:
You can do a quick check of the TA100 power pacs
Carefully test with a voltmeter on each IC
Pin 2 of each IC should show about +50vdc
Pin 6 of each IC should show around -50vdc

Then check pin 5 of each IC. If you show anything above 20mv dc, the IC is bad and preventing the protect circuit from energizing the relay. Ususally when the IC's go bad they short, resulting in high DC on pin 5 which is the output.
Click to expand...

Well that looks to be the issue. 30V and 50V on Pin 5. Looks I'll be needing replacement chips. I measured the voltages on Pin 2 and 6 and they were reversed of what you said. -50 on Pin 2 and +50 on Pin 6.
 
HPMguy said:
Check offset voltage (center of the STK emitter resistors, should be very close to zero. I've seen a bad voltage amp (differential pair(s) and current mirror) cause enough offset to keep the protection relay open.

What I usually do in a case like this is get the schematic out and start checking voltages, where they differ markedly from the schematic there is a bad part somewhere close.
Click to expand...
That is where I am at right now. Looks like the ICs are bad, but it looks like the rails are wired backwards as well. I checked voltages based on Tom B's suggestion, and the voltages are backwards from what he mentioned, and then I looked at the service manual and it does in fact appear to be wired backwards.

Someone definitely was in here before me, but they must have screwed up on rehooking things up.
 
I have been out of town and busy with work, but l I just got around to restesting some stuff and the voltages are correct! Stupid me must have had my meter probes plugged in wrong, because polarity of everything is correct.

I am going to get some non original replacement chips off ebay, and hopefully my next update will have this thing making noise. Thanks!
 
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