Help noob fix sub amp - Page 4

alsoran · 1st August 2010, 10:27 AM

OK Pin 3 0v DC, goes direct to the positive on the woofer, no further fuses between it and woofer

Mooly · 1st August 2010, 10:28 AM

Yep, got a bit of time so just have a measure and see if you can trace that connection to pin 3.

Does it go to the speaker directly ?

Mooly · 1st August 2010, 10:31 AM

OK... and also confirm that the negative terminal of the woofer actually returns to ground... just to make sure no fuse in the ground connection.

And with the amp OFF and woofer connected you should be able to read on ohms the resistance of the woofer (just to make sure that's OK) between pin 3 and ground. If you then use diode check to do same you should hear the woofer "click"

alsoran · 1st August 2010, 10:32 AM

It does, there is a sideline to a resistor then back to another pin on the IC, but no interuption between pin 3 and speaker

Mooly · 1st August 2010, 10:37 AM

OK so it clicks... so woofer is good and connected OK.

Is the IC new ?

Now a scary test... with it on and connected to the woofer what happens if you VERY CAREFULLY as in steady hands, touch a metalic screwdriver to just pin 10 of the IC. Make sure you are not touching anything else... there's no shock hazard... we just want you buzzing that input with no other voltages superimposed.

That is attempting to "buzz" the input and see if any response from speaker.

alsoran · 1st August 2010, 10:38 AM

3.5 ohms pin 3 to ground of speaker on pcb, very faint crackle in speaker on diode check. Not sure with the grounding qn, where do i put pins to check this have been using speaker ground as ground for all measurements

alsoran · 1st August 2010, 10:40 AM

IC is new, just used the negative probe to touch 10, no response, have i done right?

Mooly · 1st August 2010, 10:41 AM

3.5 ohms sounds correct. The correct ground is the 0 volt line (which will probably be the speaker return as you are using). It's that large area of print above the 1 and 2 in the picture where the two large caps have a common connection. If that reads 0.00 ohms to the speaker negative then it's OK to use that as it will be easier probably.

Mooly · 1st August 2010, 10:43 AM

You have done right but there should be response... so now we have to measure all the pins on the IC for DC voltage and see if anything seems amiss.

What's the DC voltage on pin 8 first though ?

alsoran · 1st August 2010, 10:44 AM

Yep that is the one I am using, checked and 0 ohms between that point and the negative output from transformer

1st August 2010, 10:28 AM	#32
Mooly diyAudio Moderator Join Date: Sep 2007	Yep, got a bit of time so just have a measure and see if you can trace that connection to pin 3. Does it go to the speaker directly ? __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

1st August 2010, 10:31 AM	#33
Mooly diyAudio Moderator Join Date: Sep 2007	OK... and also confirm that the negative terminal of the woofer actually returns to ground... just to make sure no fuse in the ground connection. And with the amp OFF and woofer connected you should be able to read on ohms the resistance of the woofer (just to make sure that's OK) between pin 3 and ground. If you then use diode check to do same you should hear the woofer "click" __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

1st August 2010, 10:37 AM	#35
Mooly diyAudio Moderator Join Date: Sep 2007	OK so it clicks... so woofer is good and connected OK. Is the IC new ? Now a scary test... with it on and connected to the woofer what happens if you VERY CAREFULLY as in steady hands, touch a metalic screwdriver to just pin 10 of the IC. Make sure you are not touching anything else... there's no shock hazard... we just want you buzzing that input with no other voltages superimposed. That is attempting to "buzz" the input and see if any response from speaker. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

1st August 2010, 10:41 AM	#38
Mooly diyAudio Moderator Join Date: Sep 2007	3.5 ohms sounds correct. The correct ground is the 0 volt line (which will probably be the speaker return as you are using). It's that large area of print above the 1 and 2 in the picture where the two large caps have a common connection. If that reads 0.00 ohms to the speaker negative then it's OK to use that as it will be easier probably. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

1st August 2010, 10:43 AM	#39
Mooly diyAudio Moderator Join Date: Sep 2007	You have done right but there should be response... so now we have to measure all the pins on the IC for DC voltage and see if anything seems amiss. What's the DC voltage on pin 8 first though ? __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*


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1st August 2010, 10:27 AM	#31
alsoran diyAudio Member Join Date: Jul 2010 Location: Sydney	OK Pin 3 0v DC, goes direct to the positive on the woofer, no further fuses between it and woofer

1st August 2010, 10:32 AM	#34
alsoran diyAudio Member Join Date: Jul 2010 Location: Sydney	It does, there is a sideline to a resistor then back to another pin on the IC, but no interuption between pin 3 and speaker

1st August 2010, 10:38 AM	#36
alsoran diyAudio Member Join Date: Jul 2010 Location: Sydney	3.5 ohms pin 3 to ground of speaker on pcb, very faint crackle in speaker on diode check. Not sure with the grounding qn, where do i put pins to check this have been using speaker ground as ground for all measurements

1st August 2010, 10:40 AM	#37
alsoran diyAudio Member Join Date: Jul 2010 Location: Sydney	IC is new, just used the negative probe to touch 10, no response, have i done right?

1st August 2010, 10:44 AM	#40
alsoran diyAudio Member Join Date: Jul 2010 Location: Sydney	Yep that is the one I am using, checked and 0 ohms between that point and the negative output from transformer

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