Auna ALP404CH two channels drawing exessive current when speaker connected - Page 7

Mote · 24th April 2011, 08:42 AM

With jumper wire connected from RCA shield to amps ground terminal I still have only 2V on op amps power supply legs. But speaker does not make any noises anymore and amp does not draw current with speaker connected.
Posted a real big resolution photo of the amps guts here:
http://mote.planet.ee/auna/auna.jpg
Maybe someone can see something which might be causing problems.

Perry Babin · 24th April 2011, 09:50 AM

Did you power it up like this (with the Zener out of the circuit)?

Are both of the large 220 ohm resistors getting hot?

Mote · 24th April 2011, 09:56 AM

No, I did not power it up without Zeners.
Both 220 ohm resistors get hot.

I forgot that when I took the photos, The Zener and one op amp were out of the circuit.

Perry Babin · 24th April 2011, 10:47 AM

To find what's drawing the current from the 15v supply, do the following. ALL other connections to the amp MUST be broken.

Connect pin 4 of any op-amp to your 12v power supply ground. Connect pin 8 of any op-amp to the positive terminal of the 12v power supply through the 12v lamp. The lamp should limit the current and should prevent burning traces. The shorted/leaking component should get very hot very quickly.

Mote · 24th April 2011, 11:17 AM

I let the PS run for 10 seconds and one of the op amps got hot, other 5 are cold. The one that got hot was not the one I replaced earlier and not the one I soldered PS wires to.

Mote · 24th April 2011, 11:59 AM

Replaced the op amp which got hot with another tl072 and it works.
Sound is clear, no noise, the bad channels have never played this loud. Does not draw current.
I did not remove the RCA shield -> ground jumper though or is it safe to remove it?
Now I have to test it thoroughly to see if any other symptoms appear.

Perry Babin many thanks to you again, you are the best.
Do you use this 12V to op amps legs trick often?

Perry Babin · 24th April 2011, 06:18 PM

I used to use the 12v 'trick' to find defective op-amps on the older MTX amps that were prone to regulator failure. I don't use it often for other amps but it's still a good troubleshooting technique.

If you remove the jumper and the amp again has noise, try it with a standard head unit. Some amps don't work well with portable audio sources that operate off of batteries because they have no reference to ground.

Mote · 24th April 2011, 06:43 PM

Removed jumper wire, still everything sounds good.
There is something going on with channel 1 gain pot: when adjusting volume, when I turn the pot then it kills the sound for half a second, then plays on at a new level.
I am ready to leave it be. Probably pot failure or something to do with the fact that I did not use exact same replacements for op amps.

24th April 2011, 08:42 AM	#61
Mote diyAudio Member Join Date: Jul 2010 Location: Estonia	With jumper wire connected from RCA shield to amps ground terminal I still have only 2V on op amps power supply legs. But speaker does not make any noises anymore and amp does not draw current with speaker connected. Posted a real big resolution photo of the amps guts here: http://mote.planet.ee/auna/auna.jpg Maybe someone can see something which might be causing problems. __________________ Tools: C1-76 o-scope, Weller WHS40, Mastech MAS830L multimeter, Mastech MY6243 LC meter, 16A supply

24th April 2011, 09:50 AM	#62
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Did you power it up like this (with the Zener out of the circuit)? Are both of the large 220 ohm resistors getting hot? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

24th April 2011, 09:56 AM	#63
Mote diyAudio Member Join Date: Jul 2010 Location: Estonia	No, I did not power it up without Zeners. Both 220 ohm resistors get hot. I forgot that when I took the photos, The Zener and one op amp were out of the circuit. __________________ Tools: C1-76 o-scope, Weller WHS40, Mastech MAS830L multimeter, Mastech MY6243 LC meter, 16A supply

24th April 2011, 10:47 AM	#64
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	To find what's drawing the current from the 15v supply, do the following. ALL other connections to the amp MUST be broken. Connect pin 4 of any op-amp to your 12v power supply ground. Connect pin 8 of any op-amp to the positive terminal of the 12v power supply through the 12v lamp. The lamp should limit the current and should prevent burning traces. The shorted/leaking component should get very hot very quickly. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

24th April 2011, 11:17 AM	#65
Mote diyAudio Member Join Date: Jul 2010 Location: Estonia	I let the PS run for 10 seconds and one of the op amps got hot, other 5 are cold. The one that got hot was not the one I replaced earlier and not the one I soldered PS wires to. __________________ Tools: C1-76 o-scope, Weller WHS40, Mastech MAS830L multimeter, Mastech MY6243 LC meter, 16A supply


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24th April 2011, 11:59 AM	#66
Mote diyAudio Member Join Date: Jul 2010 Location: Estonia	Replaced the op amp which got hot with another tl072 and it works. Sound is clear, no noise, the bad channels have never played this loud. Does not draw current. I did not remove the RCA shield -> ground jumper though or is it safe to remove it? Now I have to test it thoroughly to see if any other symptoms appear. Perry Babin many thanks to you again, you are the best. Do you use this 12V to op amps legs trick often? __________________ Tools: C1-76 o-scope, Weller WHS40, Mastech MAS830L multimeter, Mastech MY6243 LC meter, 16A supply

24th April 2011, 06:18 PM	#67
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	I used to use the 12v 'trick' to find defective op-amps on the older MTX amps that were prone to regulator failure. I don't use it often for other amps but it's still a good troubleshooting technique. If you remove the jumper and the amp again has noise, try it with a standard head unit. Some amps don't work well with portable audio sources that operate off of batteries because they have no reference to ground. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

24th April 2011, 06:43 PM	#68
Mote diyAudio Member Join Date: Jul 2010 Location: Estonia	Removed jumper wire, still everything sounds good. There is something going on with channel 1 gain pot: when adjusting volume, when I turn the pot then it kills the sound for half a second, then plays on at a new level. I am ready to leave it be. Probably pot failure or something to do with the fact that I did not use exact same replacements for op amps. __________________ Tools: C1-76 o-scope, Weller WHS40, Mastech MAS830L multimeter, Mastech MY6243 LC meter, 16A supply

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