TDA7396 weirdness (in an Acoustic Energy Aego M)

[lexwalker]

After much diagnostics, narrowed down the problem (of no bass) down to this TDA7396 I.C. Already tried feeding the audio directly (bypassing the preamps, via single ended config according to datasheet) into this I.C but still to no avail. Also noticed the CD-DIA pin is pulled low which means there is a problem already. Certainly due for replacement.

Now the weird part is, when I accidentally touched a floating output source to one of the input pins then the woofer started to hum loudly! But that's it, just humming but no music. Noticed the woofer goes into incursions but no excursions. My guess is one of the positive/push side drivers is internally toasted..

Is anyone here familiar with this I.C? Would like to know the normal/usual voltage at the MUTE pin.

[budm]

Re: TDA7396 weirdness (in an Acoustic Energy Aego M)

From reading the spec sheet: when the amp is in mute mode when pin 11 is low, then it goes high (>5v?) once the cap is charged up

a) The pin will have a capacitor (CM) tied to GND to set the MUTE/STAND-BY time. An
automatic Mute during turn on/off is provided to prevent noisy transients.
A resistor (RS) has to be connect between pin 10 and GND in order to program the
current that flows into CM capacitor (pin 11). The values of CM and RS determine the time required to bias the amplifier.

Stby:The device features a ST-BY function which shuts down all the internal bias supplies
when the ST-BY input is low.
In ST-BY mode the amplifier sinks a small current (in the range of few µA).
When the ST-BY pin is high the IC becomes fully operational.

Since the CD-DIA did swing low to indicate problem already. Do you see any high DC offset at the output in. If the input pin is not connected to anything, do you still get CD-DIA error?

[lexwalker]

Re: TDA7396 weirdness (in an Acoustic Energy Aego M)

From reading the spec sheet: when the amp is in mute mode when pin 11 is low, then it goes high (>5v?) once the cap is charged up

a) The pin will have a capacitor (CM) tied to GND to set the MUTE/STAND-BY time. An
automatic Mute during turn on/off is provided to prevent noisy transients.
A resistor (RS) has to be connect between pin 10 and GND in order to program the
current that flows into CM capacitor (pin 11). The values of CM and RS determine the time required to bias the amplifier.

I've got around 6V at the MUTE pin. The power supply is around 17.8V. Thus was wondering if the MUTE pin voltage is correct.

Stby:The device features a ST-BY function which shuts down all the internal bias supplies
when the ST-BY input is low.
In ST-BY mode the amplifier sinks a small current (in the range of few µA).
When the ST-BY pin is high the IC becomes fully operational.

This was one of the first things I've checked. Seems fine there, as there was 16V at this pin when coming out of standby.

Since the CD-DIA did swing low to indicate problem already. Do you see any high DC offset at the output in. If the input pin is not connected to anything, do you still get CD-DIA error?

The input pins were connected, directly to an audio source (via 220nF capacitors, also tried 1uF ones as well). Removed the SMD capacitors on the board for bypassing the board's preamps, and wires soldered directly to those empty/vacated capacitor pads. Even without any connections that CD-DIA pin was pulled low. I did notice quite a voltage at the output, in the order of around 15 to 17 volts, plus the heatsink was becoming warm easily. Well, the weird part is the satellites section are working fine thus its not shorting out the power supply. Also that hum surprised me, considering the outputs should have been dead. But (like I've mentioned earlier), no matter which input pin I've probed that floating input with, I can only see woofer incursions during the loud hum. No excursions from woofer (even put my hand on it to feel)...

[budm]

Re: TDA7396 weirdness (in an Acoustic Energy Aego M)

The large DC at the output indicates the problem, the reason I ask about having nothing connected to the input is to find out if the source has DC offset which will feed into the input of the TDA and causes DC offset at the out put.
Since this is the Bridge output setup, the Output pin 5 and pin 7 should have exact same DC voltage when measuring with ref to ground, if measured between Pin 5 and 7, then it should be in mV range.
I believe >5V at Mute pin = Un-muted.

[lexwalker]

Re: TDA7396 weirdness (in an Acoustic Energy Aego M)

The large DC at the output indicates the problem, the reason I ask about having nothing connected to the input is to find out if the source has DC offset which will feed into the input of the TDA and causes DC offset at the out put.
Since this is the Bridge output setup, the Output pin 5 and pin 7 should have exact same DC voltage when measuring with ref to ground, if measured between Pin 5 and 7, then it should be in mV range.
I believe >5V at Mute pin = Un-muted.

Roger that. Already suspected when finding quite a voltage on those output pins (when should have been almost nothing). The CD-DIA pin did gave me a quick early answer (before looking into other possibilities). By the way, very much confirm it was that I.C faulty. Replaced with new I.C and now its fully working...

Here are some pictures. #1. the internals, #2. that faulty I.C (can see the wires I've used for diagnostics as well), #3. faulty I.C pulled out, #4. new I.C in place...