TomTom 730 GO GPS - No Speaker Audio

[hgg]

Hi,

I have a TomTom car GPS unit that has been working fine for years and recently
the speaker audio stopped working.  The Line Out audio and the FM transmitting
audio are working fine, but no speaker audio.  You can select the output from the
menus.  The speaker measures exactly 4 Ohms and the connector looks fine.



The oscilloscope shows the sound wave on the line output but does not show
anything on the speaker connector.



I cannot identify these two small ICs.  The speaker is connected via two zero Ohms resistors
to the 815L1 IC.  I am not sure if its an amplifier or something else.

Any ideas on how to proceed? 
Thanks.

[wasedadoc]

Should not be too difficult to figure out that 815L1.  it is an 8 pin chip though 1 pin appears to be NC.

2 pins for the speaker, H-bridge type output.  Easily traced by PCB tracks.
2 pins for power.  Switch off and use Ohmmeter to find ground.  Switch on and use voltmeter or scope to find +ve power.
1 pin for audio in.  Use the scope to see to see if one of the 3 remaining pins has audio going in.

Expect both speaker pins to be at same voltage and around half of chip supply voltage.

IC might be similar to https://datasheetspdf.com/pdf-file/1111491/WELLKINGTECHNOLOGIES/MIX2018/1

[hgg]

Indeed, just before your reply I found that the audio signal is coming
on the far right resistor.  It is a 1K resistor followed by a 141K resistor!   
In the middle there is a capacitor to ground.  With full volume the signal at
the first resistor is 1V peak to peak.  There is no short on the IC power
pins, 4V.  It doesn't look like there is something wrong with the IC.

I am starting to think that this might be a firmware issue.
Pin 2 might be an enable pin and it has zero volts.  Hmm. 

[wasedadoc]

Enables can be active low.  That is the case with the chip I linked to.

[hgg]

Indeed, but this is a different IC.  I should measure this pin with audio
enabled and disabled to see what's going on.

[coromonadalix]

the white connector pins  are you sure they are soldered correctly,  no broken solder ? even if they seem okay ?

[hgg]

They are, first thing I've checked.
Anyway, I am measuring directly at the IC output pins and there is no audio.

[wasedadoc]

Which pin of the IC has audio going in?  I highly doubt it is via the 141k resistor into pin 3.

[hgg]

Exactly the same thought, but that was the only pin that
the oscilloscope showed a 1V p2p waveform that was
similar with the music beat as well. 

[hgg]

I measured again Pin #2 and it has zero voltage with either the Internal speaker selected
or deselected.  All pins remain at the same state regardless of whether the Internal speaker
is selected or deselected and at the same time you can measure the audio waveform on the
1k resistor on the right side.  Not sure what's going on.  PAM8302A looks like having the
same pinout.