Entertainment Center: TVs, Stereos, VCRs and DVDs - Kenwood power amp KM-106 "blown"

I just blew the left channel on my 1987 vintage power amp. Was working fine, but turned it up too loud which blew the left underrated speaker and then no sound at all from that channel even with new speakers.

I have sound on right channel.

The amp has two transistors in a push-pull configuration (2SC2821 and 2SC1215) that I can easily change (if I can find replacements), but there is another transistor (medium power) attached to the heat sink as well (C3419) that I can not guess the function of?

Any ideas on what I should replace? If one of the push-pull xstors was blown, would that prevent all sound from that channel?

Any idea where I can purchase replacement xstors?

Anybody have a service manual for it or know where I can look?

I can buy one at Sams for $20, but I could also pick up a "new" amp on Ebay for about the same price ;)

I'm an electical engineer, but I do not have any experience with sound equipment or repair.

TIA...

Chip

Have you pulled the transistors and tested them?

Hit MCM Electronics (http://www.mcmelectronics.com/) and type the part numbers in the search box. On the right it will show available substitutes.

I couldn't find anything online about it.

Not yet, I checked them in-circuit for a short... thought they'd be shorted but they are not.

MCM listed a sub for the xstor, but the sub is completely wrong... sub was a SMT med power xstor... the ones I have are large heat sink mountable xstors.

thanks for the reply!

Weird. The first part numbe came up with a completely wrong substitute. The second came up with a match. Maybe give them a call?

I don't know much about the specifics of Kenwood, but some amps in those days used mechanical relays as protection against direct shorts of the output section. You might explore that option. It might be simply a stuck relay.

There is a relay and it is pulled in... the right channel works fine.

When I move the balance to all left side, I only get very minimal sound (cross talk ?) out of the left.

I'd like to find any Kenwood Class AB amp schematic... that might help... but so far have found nothing on 'net.

I have a Concept receiver that I have blown up trying to hook up a homemade tube preamplifier to the solid state section of the receiver. My receiver have some kind of relay/circuitry that won't allow the system to turn on once a section of the amplifier is not working. Once I push the power button on, the led light is red until the the receiver checked out OK. Then the LED turn green and the rest of the circuit is turned on.

What I did was first look for any burned components. Then I took out each of the power transistors one at a time and ohm them out. Leaving them in the circuit and ohming it out that way, won't tell you if there is damage to the transistors. I replaced all four of the complimentary transistors even two of the four were bad. I was only able to buy transistors that were replacement for the one that were in the receiver. So to get better match, I replaced all four on the one channel that was blown.

I ordered my power transistor from Newark Electronic parts. Here is their link: US - Electronic Components Distributor | Newark.com (http://www.newark.com/) Their prices for the two complimentary transistors I needed for only a $2.00- $2.50 each. So that isn't to costly for them. I don't have any equipment other than the volt/ohm meter to test with. But the receiver seems to work fine and sounded just as good as before.

Hope that help here.

Thanks!

Good idea... I will replace all 4 ... they are old anyway ;)

FYI ... as for ohming them out in-circuit, if the Collector-Emitter path is shorted, then you can indeed detect this failure with the parts still in circuit.