Kenwood Receiver troubleshooting

Obviously the problem is in the output section; the first place to look. Less likely is that the protection circuitry has gone awry. For either you should get a schematic; but some initial observation is helpful. Does the unit use discrete output devices (transistors), or does it use 'chip' amplifiers?

If the chips amps, it's likely one has blown. Replace it and you're likely finished. It may have multiple identical chips you can sub to the affected channels (like from the the surround circuitry) for diagnosis purposes.

If discrete, it gets a little more difficult. It's possible that the overload took out something further up the line, ie the driver stages. Still, you might get by testing the output devices and replacing if defective. Some testing/adjusting is in order if that is the case, even after the amp is working again.

In either case, since this is a surround amp, you probably have working channels--if you bypass the 'protect' circuit--which you can use to compare your findings.

Check the Repair FAQ for more detailed information. Post any specific findings here; and people with infinitely more experience than I are likely to give more detailed help.

jak

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I obviously know the difference between a transistor and an IC chip, but I wouldn't know where inside to verify what's what. Can you give me a suggestion on where to find a set of schematics so I could start to try and disseminate what's what inside?

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Ok, I follow this logic, (no pun intended of course) but again, not knowing what's what, I won't know what to try and substitute yet

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Again, not knowing what makes up the protection circuit, I wouldn't even know the first way to go about bypassing it for testing purposes. Again, I guess Im gonna need a set of schematics first.

ific

Be glad to, could you tell me where to find the FAQ here?

Thanks for the suggestions Jak, I'll try to report back as soon as I have a chance to go further with the diagnosis on this. Vinny

It's not THAT hard. The protection circuit detects DC on the outputs, so you can look at the outputs with a voltmeter and it should be obvious at power-up which is the clunker. Sneak up the power with a variable transformer if it's too quick to shut down otherwise.

The output stage is just an NPN / PNP power transistor pair, with the emitters connected (through a high current resistor) to the output. Trace the wire to find the transistors, find the one that has shorted (usually E-C diode check will show the short). Sometimes it's the driver stage, too...

Okay, sorry that went over your head. They're going to be the biggest semiconductors on the board...either amp modules or (I think) TO-220 transistor packages. I'd have to look into my similar vintage Kenwood receiver...I think it's a discrete output (separate components).

Start your education here:

Check back. This is almost definitely fixable, although it might stretch you some. Your background should be adaptable to the task.

jak

First, thanks for the suggestions. But what may not be "THAT hard" to you, Im afraid, is at the moment, a bit lost on me. I don't have a background in electronics.. But I do have a working knowledge and a fairly competent understanding of circuits and basic solid state components and I can work my way around a soldering/desoldering station and ohm meter.

If I asked you to fix a 1992 WPC Williams Driver board based solely on a bad General Illumination circuit... what would you say to me?

Well if you are familiar with the architecture of the boardset, and the circuits employed in running that then Im sure it'd be easy for you too. Right now Im not familar with either as far as home audio, and this particular receiver. Therefore Im asking for the help I have.

I'll take the cover off again this weekend, and start to dig around. Maybe the perverbial lightbulb will turn on for me this time around. Thanks again for the suggestions. Vinny

While I have no experience with those, I would look over the board, follow the outputs back to identify the GI portion of the board, then look for the usual suspects such as cracked solder joints or obviously burned parts, then test any semiconductors with a multimeter. If it isn't raw AC from the transformer, then I would expect it to be a fairly standard linear power supply.

The same is true with an amp, or virtually any other piece of analog equipment. Look it over and get a rough visual identification of the sections, make an educated guess as to which areas are most likely to contain the problem, look for obvious visual fault indications, and then start testing the individual components for faults. In this case, test the output devices, if those are not shorted, test the driver components and bias resistors. Usually the problem will be in one of those areas, but if it isn't, work your way back. If you don't find anything shorted, apply power and verify that the supply rails are present and that the voltage is something reasonable. The schematic for any power amplifier of similar construction (discrete vs monolithic output stage) should be similar enough to give you an idea of the circuit.

First, thanks for the suggestions. But what may not be "THAT hard" to you, Im afraid, is at the moment, a bit lost on me. I don't have a background in electronics.. But I do have a working knowledge and a fairly competent understanding of circuits and basic solid state components and I can work my way around a soldering/desoldering station and ohm meter.

If I asked you to fix a 1992 WPC Williams Driver board based solely on a bad General Illumination circuit... what would you say to me?

Well if you are familiar with the architecture of the boardset, and the circuits employed in running that then Im sure it'd be easy for you too. Right now Im not familar with either as far as home audio, and this particular receiver. Therefore Im asking for the help I have.

I'll take the cover off again this weekend, and start to dig around. Maybe the perverbial lightbulb will turn on for me this time around. Thanks again for the suggestions. Vinny

I can do a Williams 7 series CPU board ... There's one in my Cosmic Gunfight ! d;~}

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