Car Stereo lost the magic smoke

[Nicko]

Hi been a big fan of EEVblog for quite some time, but finally decided to join the forum.

I'm trying to identify a blown component on a Fujitsu Ten car stereo unit/Navigation system.  Pushed it up to 11 and the magic scope escaped.  Everything still functions, except for audio output.  No markings aside for possibly a '1' or 'I' that might have survived the fallout. The damage seems pretty isolated, and subsequent cleaning reviled no additional detail.  It looks like a SOT-89 NPN Transistor. 





Any thoughts on where to look for clues.  I've had no luck trying with Fujitsu (its a H001SSC810)

[dmills]

Measure the voltage on each pin relative to the neg rail, and post them, my guess is some sort of jellybean mosfet or small power transistor (Heavy current traces to tab and right hand pin, something much smaller to the left hand pin), knowing the voltages would help.

The "I" is making me think International Rectifier, which probably means mosfet, but more information is needed.

When making these measurements use a current limited power supply (NOT a car battery).

Regards, Dan.

[wraper]

It looks like a SOT-89 NPN Transistor.

And likely it transistor but PNP, not NPN. It is for enabling power. As I understand power is coming to the emitter (pin 3), load is on the collector (pin 2), easy to check. If you short pins 2 and 3 likely it will start to work again. However it might be burn out because of increased load, like because some IC (audio power amp) failed. Check if there is no short from collector (heatsink tab) to the ground. As of replacement, find any darlington in this package which can handle enough of current which you can measure just sticking ammeter between emitter and collector.

[wraper]

Measure the voltage on each pin relative to the neg rail, and post them, my guess is some sort of jellybean mosfet or small power transistor (Heavy current traces to tab and right hand pin, something much smaller to the left hand pin), knowing the voltages would help.

Unlikely to be mosfet because there are 3 comparably "big" current limiting resistors connected to what is supposed to be base. They are useless for the MOSFET. A bit of thought. As there are x3 470R in paralel = 156 Ohm which is pretty low, likely it is not darlington, just simple PNP. Darlington will work as replacement too, though.

When making these measurements use a current limited power supply (NOT a car battery).

+1

[mb300sd]

Try looking up the FCC ID on their website. They often have high resolution pictures of the PCBs and you might get a part number.

[Stonent]

Also sold as the TomTom Eclipse II.

[miguelvp]

Try looking up the FCC ID on their website. They often have high resolution pictures of the PCBs and you might get a part number.

Funny, I just found out about that resource (using the FCC ID) by watching the chaos computer club conference as a mean for reverse engineering

[dmills]

I was in the audience, congress is an awesome event.

I concur on the probable device, PNP bipolar (But must warn that the blowup probably originated with something downstream failing).

Regards, Dan.

[Nicko]

Its an Eclipse avn4430 docking unit.  Yeah I'm pretty sure at this point TB2910HQ is not too happy with me.

Interesting however that all the FCC ID's on the labeling and manuals keep leading to only the detachable TomTom unit, nothing about the base.

It always was a terrible unit, although for about $7-8 it might not be a bad project to try to revive on a rainy day.

[Nicko]

So after coming up with a rig to hold the board upside-down while not ripping out the flat-flex, it turns out its a whopping 36mA at 5.67V.

[Stonent]

Here's my analysis (not an engineer, just following the logic)



So at the small transistor-like part at the bottom. The thin trace is probably the control voltage / current and the thicker part coming from the via would be what's flowing through.  It passes through those parallel resistors so that made me think of current limiting so I leaned towards a regular transistor, but  the part jumpering the two pins together on the big part. It looks burned as well.  If it was a pull up or pull down I would think MOSFET, also thought possibly a small clamping schottky diode?

Also the possibility of the big part being a barrier diode array and not a transistor at all.

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