[TechAssist] Re: Aiwa ADV58u amplifier-tuner , no sound

  • From: larry <schntv@xxxxxxxxxxxx>
  • To: techassist@xxxxxxxxxxxxx
  • Date: Tue, 30 Nov 2004 10:18:09 -0500

thank you again, jim.
good question, why isnt my name and address at the bottom.
i dont know
it was on the original i sent.
i checked and my signature file is supposed to be at the very 
bottom.
so i hope it works this time.
Now on the stereo.
i am slowly learning, i think.
i was confused on which ground to use for the voltage 
measurements, but now think i got it.
on all 5 push/pull 2 transistor output circuits, i read the 
same voltages, -22 on one collector and +23 on the other 
collector and zero volts on the junction of the 2 emitter 
resistors for each of the 5 sets of outputs.
so , in my opinion i see nothing wrong there.
also no ohm meter shorts between the output transistor pins of 
any of the 10 output transistors.
the tuning meter shows signal, but no audio on any of the 5 
output channels.
what do i check next??
Larry



becyn wrote:
> the relay has nothing to do with the voltages seen  on the amp board. it 
> only disconnects/connects  the  the amp output to the speaker terminals. 
> ( By the way you dont need any loads hooked up to start the process) DO 
> NOT UNDER ANY CIRCUMSTANCES  ENGAGE THE PROTECT RELAY IF LOADS ARE 
> ATTACTCHED!!!!! This will damgage the loads and do furher damage (ie; 
> smoke, flame) to the amp
> 
> I dont understand what you mean by "no voltage on the junctions". You 
> mean that literally? As in  no Vcc or Vee or just no offset at the 
> emitter swamping resistors? (low ohm ceramics)?
> Perhaps it's as simple as open fuses in the power supply?
> You need to be very precise in describing the voltages otherwise I can't 
> make head nor tails of it.
> A normal fail mode is : 1) unit powers up, but no audio out
>                                    2) all voltages present at amp and 
> everywhere else, but  a DC offset of 1volt or more can be measured at 
> the power amp's output  connection. (you must measure it at the pcb)
> You might have something else, especially if you really don't see ANY 
> voltages at the amp, but you're gonna have to do some 
> troubleshooting...or send it to ME for repair!! ;-)
> By the way, whats your company name and address?  I'm surprised that 
> Jeff didn't get on you about this!
> 
> Jim McVey
> McVey Alltronix   
> 327 Broadway
> Newburgh N.Y. 12550
> 
> Factory authorized
> service for over 20
> major brands.
> 845 561 8383
> 
> larry wrote:
> 
> 
>>thank you for the advice.
>>I do mostly tv repair but fix a few audio, now and then.
>>most the time i can check the collectors and find a short or 
>>see burnt resistors.
>>but this time none of the 5 output transistors have a short 
>>and no burnt resistors.
>>i have no voltage on the junctions of the transistors, where 
>>the outputs are connected.
>>but i doubt i would, because the relay never closes.
>>the power supply has normal voltage to the relay.
>>i am afraid to manually close the relay.
>>what is my next step?
>>Thank you,
>>Larry
>>
>>
>>
>>
>>becyn wrote:
>> 
>>
>>
>>>Are amps new to you?
>>>IF you have voltages and no output, the thing is in protect mode which 
>>>kicks in if a dc voltage is dectected on the amp out node. Otherwise, 
>>>the speaker would burst into flames-(not good ;-)
>>>
>>>No doubt one (or more)  of the amps have a dc offset caused by shorted 
>>>output transistor, drivers or problem with the differential amp. happy 
>>>hunting...
>>>
>>>Jim McVey
>>>McVey Alltronix   
>>>327 Broadway
>>>Newburgh N.Y. 12550
>>>
>>>Factory authorized
>>>service for over 20
>>>major brands.
>>>845 561 8383
>>>
>>>larry wrote:
>>>
>>>
>>>   
>>>
>>>
>>>>the readout lites, tunes stations, but no sound.
>>>>please , any clues where to start?
>>>>I have plus and minus 45 volts and also 23 volt + and -.
>>>>Larry
>>>>
>>>>
>>>>
>>>>     
>>>>
>>>
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>>
>> 
>>
> 
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-- 
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5415 N. Wooster ave.
Dover, Ohio 44622       www.geocities.com/schntv2000/
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