AMP6 Sneaky - Overload with no input?

[cnpdk]

I've just build my new AMP6 Sneaky but I cannot understand what it is doing.

Supply 12V DC - Current 75mA

Absolutely silent in the speakers even with input (line level from a Squeezebox)

Removing the active J2-jumper reduces current consumption to almost zero.

Removing the mute J2 jumper doen't change anything.

Pin 5 on TA2020 (OverloadB) is low and according to the schematics (AMP6-BASIC rev 1.2) that indicates input signal overload - But there is no signal connected.

Measuring directly on pin 10 and 13 In1 and In2 I only find a DC of 2,9V.

Any idea on what causes this and what to look for here?

Regards
Claus

[V-bro]

This seems like something is shorted on the chip pins. Perhaps a picture would clear things up both for you and for us? That is if you have a reasonably good camera....

[cnpdk]

Sorry but I have no camera able to make any usefull photos of that.

However I did a tripplecheck to see if anything was shorted and as with the first two inspections I came up with nothing.

So I hocked up the amplifier again and made the same measures. Pin 6 (not 5 as written in my first post) is still low - that is 0,6V and this time there was 2,6V DC on the input pins of the chip.

However after 5 mins consuming 75mA the amplifier suddenly drew 225mA and the chip started to get hotter.

I did a quick test but outputs were still silent.

However after power off the amplifier goes back to drawing 225mA and now pin6 (overload) is 0,0V instead of 0,6V and the inputs are 1,3V instead of 2,6V.

As I found this wrong I measured 5Vgen again and now it is dead - 0,0V instead of the 5V measured before.

I guess that the chip is dead?

Any opinions on this?

Regards
Claus

[V-bro]

Don't conclude that too quick now, it is possible the 5V collapses for a different reason. What resistance do the outputs measure? Does it unmute and if so, what's the dc voltage present on the outputs? Do all output pins of the chip measure continuity to the speaker outputs and no short circuits between them? What resistance do you measure over the 5V gen and ground? What voltage is the ref pin?

[cnpdk]

Both outputs measure approx 500 ohms.

DC voltage present on outputs are approx 300mV (out1) and 20mV (out2).

Yes all output pins measure continuity to outputs on PCB with no short circuits between them.

Resistance between 5Vgen and Ground is approx 1kohm.

REF is approx 0,45V.

Regards
Claus

[V-bro]

Outputs should measure somewhere between 15K and 25K... 500R is definitely to low and indicates something wrong. When you follow this back to the TA2020 does it stay 500R?

REF should be around 1.2Vdc if this is off more than 0.2Vdc then usually the chip is dead. But not alway! There could still be an odd state caused by something else that is wrong....

I would really like to see the soldering on this board, can't you borrow a camera?

[cnpdk]

I brought a camera home from work and made some photos.

Please see if they bring any clarity to this matter:











Apart from the three wires for testing the input all components have been soldered on both sides of the PCB.

Regards
Claus

[cnpdk]

Yes the 500 ohms goes all the way back to the chip. Well apart from a few ohms from the coils.

Regards
Claus

[V-bro]

Solders look good enough for it to be able to work.... 'fraid the TA2020 is gone then....

[cnpdk]

Solders look good enough for it to be able to work.... 'fraid the TA2020 is gone then....

Better late than never so here's an update:

Back last spring I bought a new TA2020 and a second AMP6-BASIC-SNEAKY but haven't done much about it since then.

Well today I replaced the TA2020 and the amp worked fine. The same can be said about the second SNEAKY. It just worked.

So I'm quite sure that the TA2020 was DOA.

Regards
cnpdk