Question about Kenwood KAC-7202 Car Audio Amplifier

2 Answers

Amp powers up (switchable) but has absolutely no output

Just currently bought this amp used, was told "works" but upon recieving it, it obviously doesn't.

Amp powers up best I can tell, light comes on strong and steady, cooling fan turns fast.....yet no output.
Have tried 2 different signal sources and still nothing. RCA feed lines are new and functional.....sub cabinet is new and functional.
Any suggestions?

Have Kenwood KDC 10-22 reciever/cd , doesn't seem to have RCA output as well. Any suggestions?

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  • 21 more comments 
  • Cursedknight Sep 20, 2008

    If possible, I'd like to do any and all repairs myself.

    Upon further reading through other posts, the LED is on, but it's red, I'm thinking that it's going into protect mode right away....doesn't blink or fade, just solid red....continuously.

    Being a Kenwood, should it be red or not?



    I've checked the shield ground on the HU at it checks out good at .5 ohm.

  • Cursedknight Sep 20, 2008

    What about the head unit?



    It has proper grounding at the rca's but still has no output.

  • Cursedknight Sep 20, 2008

    Ok, a bit of a headfull and a long read......but I've checked the page for possible leads as to why there's still a red light.



    I checked for shield ground on the RCA inputs and get nothing at all.



    Haven't opened the amp case as of yet............

  • Cursedknight Sep 20, 2008

    I've also checked the power suppliy at both B+ and remote terminals. Both above 13.4 V.

    Ground wire is 8g and has 0 resistance between terminal and battery post.

    All fuses are intact and functional...

    Tried all combinations of disconnecting speaker and RCA, no results.





    (With power applied)

    Have roughly 2 ohms of resistance between the Grd Term. and neg speaker output.

    Have 0v between Grd Term and RCA ground shield(s)


    Troubleshooter advises that the possibility of "shorted output transistors" is LIKELY.

  • Cursedknight Sep 21, 2008

    If I use the Ohm setting on my multi-meter I get no reaction at all....the meter doesn't change (and yes I tested probe contact reading first)

    If using the Ohm meter, it would indicate that ALL OpT's are in need of changing..... ?!?!?!?!

    If I use the Diode test setting, everything checks out fine....all pins (legs) have variable readings but nothing near 0.....actually all above 510....



    My OpT's range from a Q220-Q229..... which differs from what you said there would be. (barely, but still) some of which the probe leads have to be reversed to get similar readings...but similar readings none the less (FET's <> EFT's)?

  • Cursedknight Sep 21, 2008

    Ok, did I make any sense with any of that?

  • Cursedknight Sep 21, 2008

    OK, now.....after testing the OpT's and some cleaning of dust and or debris..... I re-checked the shield grounding of the RCA inputs, and they now show a 1.19 v test........

    I didn't take anything apart other than the case....... Maybe I didn't get a proper reading the first time?



    I'll check the Power supply transistors........as advised....

  • Cursedknight Sep 21, 2008

    All tested at like values of 0.00...... ocassionally the meter would flash a - but never showed anything other than 0.00 (in diode test mode)

  • Cursedknight Sep 22, 2008

    Would it be feasable that all 8 of them would be defective....or go "bad" all at the same time?

    Being that they're all showing the same values?

  • Cursedknight Sep 22, 2008

    What's the likely parts cost of 8 power supply transistors?

    Is it a simple enough repair for a "novice" to successfully complete?

    I'm no rocket scientist but I have been known to weild a soldering iron from time to time.

    Any special precautions I shuld take when removing them?

    I know a de-soldering pump and Braid are a must, but what about any other necessities?



    N'hey.....thanks a heck of alot in advance!

  • Cursedknight Sep 22, 2008

    Well.... "guru"....

    I've gotten all of the power supply transistors removed, the board clean and all testing done.



    1st : ALL of the PsT's are showing nothing....as in open or broken circuit

    2nd : all of the solder pads (at pins 1 and 2) are reading around 8.3v - 8.5v...



    is this good, or bad?

    And what's next?



    Obviously I need to get the PsT's..... but does the voltage difference indicate a need for more testing and parts? :(



    I did get the board nicely cleaned and relatively solder free, making sure there are no crossed circuits.

  • Cursedknight Sep 22, 2008

    Ok, my mistake.....I wrote a bunch of it down and read some of it wrong when posting it here.......



    I feel pretty lame right now!



    All pads are reading at 4.3v - 4.5v.....



    This would seem to be a good thing, no?

  • Cursedknight Sep 22, 2008

    they read as if the leads aren't touching anything

  • Cursedknight Sep 22, 2008

    with the tester on Diode check.....those same pads, in the same order and sequence, show 1413 - 1417

    v?

  • Cursedknight Sep 22, 2008

    I couldn't tell you why it's reading differently.

    Everything prior to removing the power supply transistors was in it's original factory condition as far as I could tell.

    Should the power up LED be red for this model, or should it be a different color?



    "No individual transistor should read near 0 ohms between any if its legs. If you find any that read near 0 ohms, you need to remove them so you can check them out of the circuit."



    Which is it? ohms or volts?

  • Cursedknight Sep 22, 2008

    I've been using the diode test mode for all of the transistor testing, and dcv to test the pads.



    I'm gonna pull 4 of the output transistors to test them off the board now.

  • Cursedknight Sep 22, 2008

    ok, if what you say about testing pin (red) 1-2 (black).... and so on is to be taken as gospel ..... out of the board, the four that I had suspicion of aren't showing any values.

    If I reverse the polarity (red to pin 3) I only get current through to pin 1 and not 2



    Their board placements are : Q222, Q225, Q226 & Q229

    Three of the parts are marked : A1694

    48 P



    And the fourth is marked: A1694

    48 Y



    There is a local Electronics supply store (that's NOT Radio Shack) that distributes nationally, should I just take the parts with me? and are these a fairly common part that should be stocked?



    I do think that these are the problem.

  • Cursedknight Sep 22, 2008

    the 1st diagram shows red lead to pin 1, black lead to pins 2&3 stating that readings should be between 0.5 & 0.7 v

    In this configuration, all four show as if leads not touching.



    the 2nd diagram shows black lead to pin 1, red lead to pins 2&3 stating that there should be NO current



    the 3rd diagram shows black lead to pin 2, red lead to pin 3 and vice versa, stating there should also be NO current



    I'm taking it that these are PNP as opposed to NPN



    You're the guru, I'll re-install them and try to get it to power up...

  • Cursedknight Sep 22, 2008

    I gathered that much from the emitter and collector diagram



    I tried to convert the images to .jpg but for some reason this computer wouldn't let me. So they're in a Microsoft Document Image file

  • Cursedknight Sep 22, 2008

    alright I'm going to re-install all of the parts and try to get it to power up

  • Cursedknight Sep 22, 2008

    done and done....

    powers up like it did before, but no change in output signal

  • Cursedknight Oct 03, 2008

    Perry, please!



    There's got to be something insanly simple keeping this amp from working!

    Still "powers" with led and fan, but no output.....went through all of that rigamarow and got nowhere, essentially.

    Have verified a 2 mV signal getting to it, but still nothing coming out.

  • clause19 Oct 19, 2008

    I have the same problem as you do. I took the amp into a shop and the guy told me it was 2 blown zener diode's. It was like 150 to fix so I said screw it . But im trying to find out where the diodes are in the circuit board.

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  • Expert
  • 68 Answers

Hey cursedknight, I know this is an old post but let me know if you
got your KAC-7202 amp fixed cause I can help you. I have the same amp with some output transistor problems or power supply transistor problems. You can remove the bad transistors that are reading bad and power up the amp and it will work, not all amps will but some. I have an Insignia amp I am workin on and found one bad power mosfet transistor there are 3 per side. I took all 3
on the side that I found the bad one on and powered it up and it worked, but with half the power. Try doing that, if you find one bad
take tall them out on the side you found the bad one on and put power to it. Same thing goes for output transistors. Go to youtube
and type in car amp repair and there are 9 videos of a guy showing you some really good repair tips and also go to www.bcae1.com this guy has all the info and a dvd rom you can buy. On his site there is alot that will help. Good luck

Posted on Feb 02, 2009

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  • Master
  • 631 Answers

If possible return the amp to the seller for a refund (before you tamper with it).

If that's not possible, the amp will need to be repaired. Do you want to try to repair it yourself?




For the head unit, you need to check the shield ground first. The following page will show you how to perform the test.

Shield Ground Test/Repair

Let me know if you have any other questions.

Posted on Sep 19, 2008

  • 13 more comments 
  • Perry Babin Sep 20, 2008

    At the top of the page (link) I posted, there are two links to aid in troubleshooting an amp that's going into protection. If the first page indicates that the amp is damaged, read through the second page. The second page will help you find defective components. Let me know if you have more questions.




  • Perry Babin Sep 20, 2008

    The head unit will likely be more difficult to repair. Let's deal with the amplifier first.

  • Perry Babin Sep 21, 2008

    You need to disconnect the amp from the power source and check the output transistors to see if they're shorted. No individual transistor should read near 0 ohms between any if its legs. If you find any that read near 0 ohms, you need to remove them so you can check them out of the circuit.

    The output transistors are Q222-Q229.

    Let me know what you find.


  • Perry Babin Sep 21, 2008

    Check the power supply transistors (Q3-Q8).

    If none of those are defective, the next step would require testing with the amplifier powered up.


  • Perry Babin Sep 22, 2008

    If they read 0.00 in diode check mode between the first and second legs, they're defective. You should pull them to confirm but 0.00 from 1-2 is almost always indicative of shorted transistors.

  • Perry Babin Sep 22, 2008

    When one goes, the rest are likely to fail also.

  • Perry Babin Sep 22, 2008

    It should be a simple repair but there are no guarantees that you will be able to successfully be able to repair it.

    After you get the old FETs out of the board, you need to power up the amp (including remote) and measure the voltage on the solder pad for the first leg of the FETs. They should all read ~4-5 volts. If you read something near 0v, something near 12v or there is a significant difference between the various FETs, let me know. It could indicate there there is more damage.

    The FETs won't be expensive. Don't order them until you check the voltage on the gate pads (described above).

    mouser.com
    844-IRFIZ44GPBF

    If you want a good desoldering pump (one that actually works):
    http://www.mcmelectronics.com/product/21...

    Radio shack has desoldering braid. If you use the RS braid, pick up some of the paste flux also. Their braid isn't always fresh and the paste flux will help it work as it should.

    To clean the board of flux, use acetone and a toothbrush (outside, read instructions, don't use a toothbrush made of transparent plastic, it will melt in the acetone).


  • Perry Babin Sep 22, 2008

    4.3-4.5 is OK.

    Do the FETs you removed read 'open' or '0 ohms' from leg 1 to either of the other legs?


  • Perry Babin Sep 22, 2008

    That means that they are probably OK.

    You tested them in the board and read 0.00v on diode check. Across those same points on the board, do you still read 0.00v?

  • Perry Babin Sep 22, 2008

    What do you think caused you to read 0.00v before and now you're reading well above 0v?

    From the latest readings, it appears as if the amp should work if you reinstalled the FETs. If you do reinstall them and apply power to the amp, do so via a single 15 amp fuse and have the FETs tightly clamped to the heatsink.




  • Perry Babin Sep 22, 2008

    The LED should be red as far as I know.

    If the meter is on diode check, the readings are in volts. If the meter is set to ohms/resistance, the readings are in ohms.


  • Perry Babin Sep 22, 2008

    Those parts are probably OK. They are BJTs, not FETs and you have to check them differently. If none read close to 0.00 on diode check, they're likely OK. Most BJT outputs short when they fail.

    There was a link to a page that shows you how to check most transistors on the basic repair page. Did you follow that link?

    As I said before, I'd reinstall the transistors and power up the amp via a 15 amp fuse. If it doesn't power up, we'll have to check the voltage at various points (meter set to DC volts).


  • Perry Babin Sep 22, 2008

    Use the form on the basic repair page and send me the screen caps.

    When checking, you need to use the correct test procedure. The tests shown are for NPN BJTs and N-channel FETs. For PNP BJTs and P-channel FETs, you must reverse the leads.


  • Perry Babin Sep 22, 2008

    Remember... All transistors clamped to sink and 15 amp inline fuse.

  • Perry Babin Oct 03, 2008

    The 0.00 readings on the power supply FETs led us in the wrong direction.

    There is an IC labeled TL494 (IC5 on the board). Clamp all transistors down and power up the amp. Measure the DC voltage on all 16 pins of the IC and post them here. Place the black meter lead on the chassis ground terminal when measuring the voltage.


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