Question about Cadence A7 HC Car Audio Amplifier

2 Answers

Have a a7 Hc... Blown transistors.. Shematic diagram??

One off the transistorleader have short surcuit to gnd in output channel.

Have changed all transistors but hven i power on the amp i get ca 40v dc on the speaker conections. Then i took the power off to not blow any thing. Transistors in power suply starting to get hot after a short time. What do i need to change??

I need a schematic diagram in pdf file. Can you help me??


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  • 8 more comments 
  • Torbjørn Paasche Jun 24, 2008

    part numbers are irf3205 in powersuply, and irf9640 in the output section.

    Yes.. This amp has ICs labeled B52 and F16. Hven i look under one transistor irf9640 i can see two marks after the old transistor have short surcit to the chassis on this amp.

    The old transistor have bended legs. And suddently under driving transistor short surcuit to the chassis. I have replased all 3205 and 9640 transistors.

  • Torbjørn Paasche Jun 24, 2008

    I am shore power suply is working korektly. Even the green diode is on when i turn it on. But i must take off the remote power to not blow transistors after ca 10 sek. They are getting very hot without any load.


  • Torbjørn Paasche Jul 21, 2008

    I used the amp meter and i blow the fuse in it. Luckily i have more fuses...

    ..Yes ... 10A fuse blown avay... When i power up, all transistors are getting hot in a short moment.

  • Torbjørn Paasche Jul 22, 2008

    Like you said i pulled out the rectifiers and then i powered up...
    And the green light came on an the amp stays on, and the fuse dident blow..


  • Torbjørn Paasche Jul 22, 2008

    Now i have mounted rectifiers and removed all tvelve irf9640

    i found one of them is broken. Hven i used the multi meter i found other values than it stands on the link. But i look up the transistors and found out that they are p- channel so i guessed that i just change posetive and negative hven i tested transistors. I found out that drain source readings are between 0,896V and 0,936V

    -positiv probe on drain

    -negativ probe on source

    I have one computer oscilloscope.

    I turned on the amp and its good. No heat transistor in powersuply at all

  • Torbjørn Paasche Jul 22, 2008

    i guess that this is the wrong whith the amp....

    i have replaced all with irf 9640...

    do you know how they have to be placed

  • Torbjørn Paasche Jul 22, 2008

    then i feel sure that ther is 4 of 640s transistors

    I must order parts then...

    do you think that anything is broken because of this mistake i have done?

    or shall i just try it on??

    I can notify you when i get irf 640s. I guess it vill take a week

  • Torbjørn Paasche Jul 22, 2008

    i have tested all 1027 and 1023 with the diode test and ohm test. they seems ok..

    the distributor dident have any of those.

  • Torbjørn Paasche Aug 23, 2008

    Today i resived the parts. I solider them on place and then i use a 10amp fuse and powered up... Fuse dident blow.... Is that a good sign?? I guess so:-)

    I havent tryed the amlifier yet...

    are there anything else i shold be ware of?

  • Torbjørn Paasche Aug 23, 2008

    I have now monted the amplifier and tested it....

    it works great..


    You have helped me out...

    Thank you ... very mutch...



2 Answers

You just need to send this amp to cadence they will get it fixed in less then a week trust me i sent mine through ups it only cost me 35$ for shipping and they charged me a 1 dollar to fix and if you do not believe me i got proof.

Posted on Sep 30, 2008

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What are the part numbers on the transistors you replaced?

Did you replace transistors in the output section and the power supply section?

Does this amp have the defaced ICs labeled B52 and F16?

Posted on Jun 23, 2008

  • 6 more comments 
  • Perry Babin Jun 24, 2008

    Do you know how much current the amp is drawing when you power it up?

    If you don't and don't have an amp meter, insert a 10 amp fuse in the B+ supply line. If it blows, it's drawing excessive current. If it doesn't, the power supply FETs may have defective drivers. Let me know what you find. We have to make sure the power supply is OK before we can move to the audio section.

  • Perry Babin Jun 24, 2008

    We MUST know if it's drawing excessive current. Does it blow a 10 amp fuse when powered up?

  • Perry Babin Jul 21, 2008

    Pull the rectifiers (the ones on the heatsink) and power the amp up (through the 10 amp fuse). If the fuse blows, the power supply has a fault. Pulling the rectifiers will isolate the audio and power supply sections so you can determine which section has a fault.

    Let me know what you find.

  • Perry Babin Jul 22, 2008

    If the power supply transistors are not getting hot, the power supply is likely OK. The excessive current draw is likely due to a fault in the audio amplifier.

    There could be a number of problems. The first thing I'd suggest is to remove all of the output transistors (IRF640s and IRF9640s from the board and make sure that none are leaking (electrically).

    With your meter set to ohms, there should be 'absolutely' no continuity between the first leg of the transistor and either of the other legs of the transistor. If there is any continuity (even if it's thousands of ohms), the transistor is defective.

    Go to the 'Checking Field Effect Transistors' section of the following page. It will tell you how to properly check the transistors for other faults.

    Checking Semis

    With all of the outputs out of the board and the rectifiers back in the circuit (be careful that you get them in the correct location), the amp should power up and should not blow the fuse.

    Do you have an oscilloscope?

    Let me know what you find.

  • Perry Babin Jul 22, 2008

    In the audio section, there should be ~40% IRF640s and 60% IRF9640s. They shouldn't all be 9640s. Do you have both 640s and 9640s?

  • Perry Babin Jul 22, 2008

    The third leg of the 9640s goes to the positive rail. The third leg of the 640s goes to the negative rail.

  • Perry Babin Jul 22, 2008

    I don't think this mistake would have caused any other damage. There may be damage from the original failure of the transistors.

    Order new 9640s also. Even if they check OK with a meter, they could have been damaged when you installed them in the wrong locations.

    If you're ordering from a distributor that has 2SA1023s and 2SC1027s (likely used as drivers) order several of each. There are also two 12v Zeners. I don't know if they're 1/2 watt or 1 watt. Order replacements for those also.

    Let me know what you find when you get the replacements.

  • Perry Babin Aug 23, 2008

    Don't operate the amplifier unless the transistors are tightly clamped to the heatsink.



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