Loud Thump from Subwoofer when switching inputs on Pioneer VSX-D939TX receiver

[Peter Qiu]

Hi Everyone,

I got a Pioneer VSX-D939TX receiver connected to INFINITY Primus PS212 Subwoofer via receiver's Subwoofer Output. As and when I switched the Audio inputs on this receiver, a very LOUD Thump (Popping) from the Subwoofer !!!

Need help !!! Does anyone know the root cause and enlighten me how to fix it or is there a schematic to add in between the Receiver and Subwoofer to eliminate Popping?

Thanks in advance,

Peter Qiu.

 

[JonSnell Electronic]

Seems that the muting circuit in the Pioneer is malfunctioning. Check the A Mute 2 line.

 

[JonSnell Electronic]

Check Q903. It inverts the A Mute 2 signal.

 

[norman bates]

My outlaw 1050 receiver did that, right out of the box.

I had a Yamaha receiver do it too after 6 months.

 

[Peter Qiu]

Hi JonSnell,

Thanks for pointing out the problem !

It was Q903 faulty (SMT, PNP digital transistor, DTA124EK). There was a high resistance between Base and Emitter, from the data sheet, R1+R2 should be 44K ohm. Replacement was done on the receiver and no more Thumping from the Subwoofer.

 

[Peter Qiu]

Hi JonSnell,

There's another issue coming out...I connected the "Subwoofer Out" output jack of VSX-D939TX into JBL Amplifier Input jacks (regardless of CD input, AUX input.....), my JBL Amplifier went into protection mode (relay cut off, red LED turned on). In order to confirm the root cause, I went back to connect it into INFINITY Primus PS212 Subwoofer and it worked well !!!
Further investigation revealed that there was -8.54VDC presence at "Subwoofer Out" of VSX-D939TX, just wondering how/where this DC VOLTAGE came about??? Please enlighten me....thanking you in advance.