My wife is rough on cords - always twisted - and today her electric tire pump reportedly made a smell and quit. This is a pump that plugs into a car's accessory hole. It displays the pressure and can automatically fill to a tire a programmed limit. Handy.

The power wires at the cigarette-lighter plug never had proper strain relief. They looked like they did, but the wires could move easily inside the grommet? and so the strain went straight to the solder joints inside. They came apart today. So I got that diagnosed and all cleaned up with fresh solder and some thermoset glue to actually provide some protection. Plugged it in and ... nothing.

I've confirmed that there is ~12.5V on the PCB when it's plugged in, so at least I can have a little satisfaction that my repair had succeeded. But it's completely dead. I don't see any sign of burning and since these things are pretty cheap these days, it's really not worth additional work. I'm posting pictures of the guts here so people can see how these things work.

I'm considering repurposing the hardware into a simple on/off pump. The mechanicals work fine as far as I know. It's the PCB control board that has failed. It'd be nice to read the sensor but I imagine that requires more than a simple solution.

 

Whoa, now that I look carefully at the photos, there is a component to the right of the display that does look cooked after all. Any idea what that might be?

 

Not only that, but by the flux residue it looks like it was replaced. A repair done during assembly?

 

It appears to be a transistor used to control the N-Channel MOSFET (Q2) that powers the pump.

 

Can you make out the markings on the cooked chip? Looks like 'B32A' ??
Have you confirmed that the motor winding is intact?

 

Looks like 'B32A' ??

I agree. Haven't found anything on that yet. @Ya'akov may have narrowed the search.

Have you confirmed that the motor winding is intact?

Not yet but I have no reason to suspect it, since the control board is dead. Normally the device lights up the display and shows a pressure before you turn the pump on.

 

It appears to be a transistor used to control the N-Channel MOSFET (Q2) that powers the pump.

Would you suppose that the tab is tied to one of the pins?

 

Meta AI says
"3 leads + wide tab = SOT-223 or SOT-89. With that marking it's almost certainly: B32A = AMS1117-3.3 / AP1117-3.3 / NCP1117-3.3 - 3.3V 1A LDO regulator. That's the standard marking for that package. B32 = 3.2/3.3V family, A = date/lot."

 

Interesting.

Would you suppose that the tab is tied to one of the pins?

I think @Alec_t has ir right, it's probably a 3v3 regulator powering the MCU. I didn't notice the second via that could connect the one in the MOSFET's trace to the trace that runs under the MCU.

 

If something happened that fried that regulator, there's a pretty good chance that other things, like the MCU, got damaged as well. Probably even more likely that something else got damaged and that is what led to the regulator getting fried.

 

My experience has been that, when a regulator has let the magic smoke out, it will allow most of the input voltage to pass thru. In which cas, your microcontroller will be toast, too.
Having said, the 1117 are very inexpensive, so it may be worthwhile to replace it and power it up again, because -fingers crossed- the microcontroller may have survived. Unlikely, but it might.

EDIT: WBahn beat me to the response. But you can see I'm in agreement with his evaluation.

 

...the 1117 are very inexpensive, so it may be worthwhile to replace it and power it up again..

The part may be cheap but the delivered price may be prohibitive.

I happen to have a decent DC power supply and so it may make sense to apply 3.3V, perhaps with a current limit of 100mA?, to the middle Vout pin, to see if the board wakes up.

Would you remove the old part first? Cutting that middle leg maybe easier.

 

The part may be cheap but the delivered price may be prohibitive.

I happen to have a decent DC power supply and so it may make sense to apply 3.3V, perhaps with a current limit of 100mA?, to the middle Vout pin, to see if the board wakes up.

Would you remove the old part first? Cutting that middle leg maybe easier.

Yes, remove the damaged part, since it might have failed as a short.

 

Amazon has a lifetime supply for 9 bucks.

 

Wow, that's crazy. Thanks.

 

With the part removed and 3.3V supplied to the middle pad, nothing. Could it require the 12V supply as well to wake up? It obviously needs it to run the pump, but to wake up?

 

The more likely explanation is that the board is simply cooked (which could mean just the MCU or could mean any combination of components are damaged or possible that just the PCB itself has developed a fault.

 

You would have to trace the 12V supply to determine whether it goes somewhere else besides the regulator itself.
Another strategy, supply simultaneously both the 3.3 and 12 v supplies.
But most likely outcome is what W has suggested.

 

It's a little tricky for me to supply both voltages at the same time but I suppose I'll give it one last gasp. Two aging 9V transistor batteries in series might work.

 

It's a little tricky for me to supply both voltages at the same time but I suppose I'll give it one last gasp. Two aging 9V transistor batteries in series might work.

If they are that aged, then they may not be able to deliver enough current to suffice, even if the pump isn't running.

Can't you supply the 12 V from the power outlet in the car and the 3.3 V from your other source?