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Need Help Hello, I'm having trouble repairing a kenwood DTS Amp model: KRF-7775D. I have the service manual but still could not find any faulty components. Problem with this is that it works on it's own, seems it has a mind of it's own, so I seviced and replaced the memory backup caps near the main u-com and it fixed the "Mind" problem. Now it's doing exactly what I want it except no Audio output. checked everything, output stage, protection, muting etc. no luck. But if I remove the DSP assy ( which has the DAC's, sub u-com and the DSP chip) I can get audio from the dvd 6 channel direct input. sounds great. but if I insert the card the damn thing goes mute. so I checked the card ( voltages and the resets) found that the DSP power (3.3V) is missing. the funny thing is this voltage is present at power on and dies when the protection relay switches on and mute deactivates. The DSP is powered down and is not activated in any sound modes or input modes, so my guess is with the DSP power down the DAC's are not workin, and with the card removed the u-com bypasses this stage. I replaced the sub u-com chip but nothing happened. further checking revealed that after the sub u-com recieves the master reset from the main u-com, it powers down the 3.3V AVR. So after few seconds the after power on the 3.3V dies. I donno why, cud not think of anything, but I did find the master clk from main u-com to the sub u-com is at 3 volts. But to my knowledge it should be 3.3V. Cause it the clk goes via level shifter 5V-3.3V IC. so the input being at 5V with no data or clk output is 3V. All the gates of this IC show's 3.3V at high level. So may be this is a problem but the funny thing is I can see the clk from this out put, when change the sound modes which indicates the sub u- com is RX'ing it's data. so wht gives, why no sound. Pls can any one give me a hint on this issue. Rifaa

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  • Rifaa-ath Razei
    Rifaa-ath Razei Sep 06, 2007

    Hey Thanks replying. Do u mind if I ask u who u r? and also u'r experience in this field. I just like know who I'm talking to.
    Any way I tried some more tonight, replace the level shifter ( the buffer only ) with a CMOS schmitt and the still the same 3V out put but now the clk is more clean, I mean strong, but still nothing the DSP is still powering down, so I checked the MDT port, which is the Master data to the sub u-com. And guess what no data what so ever, I mean the port doesnt even open at power on, (I use a little trick in measuring the ouput of digital gates, the complimentry otputs and it's undefined state at power on, I hope understand)what I do is I measure the continuity at the ouput with my DMM at diode check, this way I can here beep inturrupts when the gate is switching either at reset, power on or signal, always had worked this way. :)
    So at power on I can get beep inturrupts at clk, Master rst, sub rst, sub master request and sub slave request but nothing at the MDT ( Data output) all these pins is at the master u-com and goes to the sub u-com (which controls the full DSP functionality of the whole amp). So know I'm done, I can't go no further, My guess is the level shifter is working (probably) can't be sure without a scope. I can get the level shifter from china any time cause i got the sub u-com too. hehe.
    But the problem is I'm not sure what the problem is, the main u-com or the software itself or is it initializing fault becuase the backup caps were replaced or damaged, I dunno. Any one can suggest anything, all I need is seggestion, I can do anything almost if it doeas not involve a scope, cause it is way out of my budget. other than tht I can tackle any problem with the proper resources. Guys please help.

  • Rifaa-ath Razei
    Rifaa-ath Razei Nov 11, 2008

    Well after a long struggle, the problem was the golden capacitor. He hehehehe
    Problem solved



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I think you've answered your own question, circuit power is not going from one side of the DSP chip to the other and that suggests that the DSP's core is at-least partly DOA. You are indeed correct that functional power should be at 3.3V and yes 0.3V does make a difference to the components that rely on a 3.3V feed, however if the DSP is fried you are not going to see normal functionality or be able to diagnose further.

Posted on Sep 05, 2007


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First of all my nick is Rifaa.
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My receiver is experiencing the same issue now. I was thinking it was an amplifier output stage going out. I only took the hood off and measured some typical voltage areas, nothing too in depth while on the living room floor. What was your conclusion? I'd much rather fix mine than buy a new one.

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