Kenwood Kac-819 won't power up!

thejulianath20 · 7th July 2011, 05:09 AM

My kenwood Kac-819 worked perfect for years in my old car. I took it out when I sold my car and now I installed in my new car with my Alpine CDA105 and it won't power up! I took it into Best buy and they bench tested it and it powered for a second but tripped their connection.... I don't understand what could have happened from one car to the next! I took it apart now and it looks clean and everything seems connected and nothing looks blown...

Please help.

Perry Babin · 7th July 2011, 08:37 AM

It may have shorted output transistors.

If it tripped the protection in their power supply, it should have blown the fuses when you installed it. Did it blow the fuses?

thejulianath20 · 7th July 2011, 04:37 PM

Both fuses are perfectly fine. They both have continuity too! They are both 30amps. Which is what came with the amp when I bought it years ago.

thejulianath20 · 05:41 PM

How do I check for shorted output transistors? How much would it cost for me to just replace all 4? Also is it as easy as just unscrewing and then screwing the new ones down tight?

Perry Babin · 7th July 2011, 08:41 PM

Have you read the entire basic amp repair page yet? If not, (link in sig file below), do so now.

There's no point in replacing parts if you don't know if they're defective.

thejulianath20 · 7th July 2011, 09:14 PM

So if the output transistors are shorted or just one of them is, it would stop the whole amp from powering up?

Also nothing personal, but for basic that guide is WAY in depth and overwhelming...

If it will only cost me like $5 for all 4 output transistors then I would do that in a heartbeat!

How Do I Test them?

Perry Babin · 7th July 2011, 10:03 PM

The tests are producing conflicting results. I'm assuming that they used a power supply that works well to power up other amps. If that's true, enough current draw to shut it down should be sufficient to blow the fuses.

The outputs for this amp appear to be ~$10 each plus shipping (pacparts and kenwoodparts).

You should not read anything near 0 ohms between the legs of any individual transistor no matter the probe placement on that transistor.

thejulianath20 · 7th July 2011, 11:39 PM

So red probe on left leg and put black probe on middle then read and then black on right probe and read?

Do this for all output transistors?

My readings "should not read anything near 0 ohms between the legs of any individual transistor"?

thejulianath20 · 04:12 AM

Well here is what found doing the ohms tests on all 4 of the output transistors. I had the meter set to 200k on the ohm setting.

The readings that I put 1__._ they are the same as no connection; probes not touching anything or themselves!

Perry Babin · 8th July 2011, 05:05 AM

None appear shorted but that's a bit of a guess since you didn't include the units. I'm assuming that all are k ohms. If you would have filled in the other blanks with the meter set to diode check, it would be more definitive.

7th July 2011, 05:09 AM	#1
thejulianath20 diyAudio Member Join Date: Jul 2011 Location: Arizona	Kenwood Kac-819 won't power up! My kenwood Kac-819 worked perfect for years in my old car. I took it out when I sold my car and now I installed in my new car with my Alpine CDA105 and it won't power up! I took it into Best buy and they bench tested it and it powered for a second but tripped their connection.... I don't understand what could have happened from one car to the next! I took it apart now and it looks clean and everything seems connected and nothing looks blown... Please help.

7th July 2011, 08:37 AM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	It may have shorted output transistors. If it tripped the protection in their power supply, it should have blown the fuses when you installed it. Did it blow the fuses? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

7th July 2011, 05:16 PM	#4
thejulianath20 diyAudio Member Join Date: Jul 2011 Location: Arizona	How do I check for shorted output transistors? How much would it cost for me to just replace all 4? Also is it as easy as just unscrewing and then screwing the new ones down tight? Last edited by thejulianath20; 7th July 2011 at 05:41 PM.

7th July 2011, 08:41 PM	#5
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Have you read the entire basic amp repair page yet? If not, (link in sig file below), do so now. There's no point in replacing parts if you don't know if they're defective. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

7th July 2011, 10:03 PM	#7
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	The tests are producing conflicting results. I'm assuming that they used a power supply that works well to power up other amps. If that's true, enough current draw to shut it down should be sufficient to blow the fuses. The outputs for this amp appear to be ~$10 each plus shipping (pacparts and kenwoodparts). You should not read anything near 0 ohms between the legs of any individual transistor no matter the probe placement on that transistor. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links


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7th July 2011, 04:37 PM	#3
thejulianath20 diyAudio Member Join Date: Jul 2011 Location: Arizona	Both fuses are perfectly fine. They both have continuity too! They are both 30amps. Which is what came with the amp when I bought it years ago.

7th July 2011, 09:14 PM	#6
thejulianath20 diyAudio Member Join Date: Jul 2011 Location: Arizona	So if the output transistors are shorted or just one of them is, it would stop the whole amp from powering up? Also nothing personal, but for basic that guide is WAY in depth and overwhelming... If it will only cost me like $5 for all 4 output transistors then I would do that in a heartbeat! How Do I Test them?

7th July 2011, 11:39 PM	#8
thejulianath20 diyAudio Member Join Date: Jul 2011 Location: Arizona	So red probe on left leg and put black probe on middle then read and then black on right probe and read? Do this for all output transistors? My readings "should not read anything near 0 ohms between the legs of any individual transistor"?

8th July 2011, 05:05 AM	#10
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	None appear shorted but that's a bit of a guess since you didn't include the units. I'm assuming that all are k ohms. If you would have filled in the other blanks with the meter set to diode check, it would be more definitive. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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