TomTom XL Fuse Blown. Green Light But No Charge

[TechSaviour]

Hi,

I have a TomTom XL N14644 which is showing the green indicator when connected to a power source but the charge isn't getting to the battery.

Looking at the PCB it's obvious that a fuse has blown and I think replacing the fuse will solve the problem. Unfortunately I don't know what type of fuse it is or where I can buy a replacement. Take a look at the attached picture. Perhaps someone will know what this is and where I can buy a replacement.

Many thanks in advance for any help provided.

Dave

 

[canderson]

No such model as an N14644 (that's a regulatory cert number), but we can see what you have. Are you certain that the blown component isn't a zener diode? 99 times out of 100, that's what goes toast. On many of the the other models, you'll find them called D5. Blown SMT fuses should NEVER look like what you've identified in any case.

Please see if you see the "D" nomenclature near that part on your board. If so, it's going to be a 5.6V zener. I've never opened an XL, so can't tell you which way cathode/anode are set up, so I hope you can still see the stripe on the part or give us a hand figuring out which side is DC ground on that board.

 

[TechSaviour]

Hi canderson,

Thanks for taking a look.
TBO I'm not sure what type of diode it is so I can't tell you if it's a D5. I receive these all the time and the same SMD has always blown and looks the same (burnt out). They always have the green light indicator when attached to a power source but the charge never reaches the battery.

I've taken a picture of the same area on a perfectly working XL PCB and circled what the diode should look like. Inscribed on the part is either an 8 or a B. Take a look and let me know what you think.

I've also taken a picture showing the full PCB on the side where the burn out has occurred. The other side of the PCB has no signs of damage.

Many thanks in advance for anyone's help.

Dave

 

[canderson]

Well crap, Dave... they weren't bothering to silk screen the component designators on those boards! I see why this is harder than it should be for you.

Based upon the photo of your intact board, I'm going to go out on a very short limb here and say you are looking at the zener on that board as well. It's been a known weak spot forever. Here is one that I have recommended before and has successfully been sourced and used as a replacement for this troublesome component (and yes, it's a 5V part) on your side of the pond
http://uk.farnell.com/stmicroelectronics/sm2t6v8a/transil-200w-unidirect-do-216aa/dp/1749297RL

The good news is that you've got a shot of one still uncrisped, so you'll be able to correctly identify the polarity without problem.

One last bit of advice. Not infrequently, it has been a transient or permanent failure of the car charger that takes out the zener. I'd be very suspicious of whichever charger was connected when this component failed.

 

[TechSaviour]

Hi Canderson,

Thanks for your help. I'll buy a few of these and see if they fix the problem.
I'll report back once I know one way or the other.

Cheers again for your time.

Dave

 

[canderson]

Yes, please let me know.

It seems that for SOME reason, TomTom was sufficiently concerned about voltage drop over their meter or so of wire between the car chargers and units that they added a remote sense wire from the device back to the supply on the 5th USB wire. If you lose continuity on any of the other wires, it either won't matter or the device will stop working. If you lose the white wire, the charger sees this as a 'low voltage' condition and promptly cranks the output of the charger to the max, whatever that is. And whatever that voltage is, it's evidently > than the breakdown voltage of the zener, and the zener doesn't think much of having to deal with the resulting current on a continuous basis, and .. well, you know what they say .. it all runs on smoke, and if you let the smoke out, nothing works.

FWIW, I've seen those 5V zeners do just fine, but rumor has it that the OEM part is actually a 5.6V. I suppose it would do to measure one in-circuit with the thing running to be certain. If it is supposed to be 5.6V, a 5V zener might have to do a little extra duty as a transient voltage protector.

 

[Garygadget]

Hi are you sure you Just don't need a new battery.
My tomtom one had the green light on but would not charge battery.
I bought a new battery from amazon.co.uk .
Fitted easy and now it charges up battery ok.

 

[canderson]

@Garygadget
If you look at the photo in his first post, you'll see that a battery is presently the least of his problems, if indeed he has a battery problem.

As I mentioned in my last post, "It all runs on smoke, and if you let the smoke out, nothing works."

 

[Garygadget]

I was only saying No need to get on your high horse,that's what these forums are all about to help one another giving different ideas.
my tomtom did not turn on but green light worked.
and when I opened it up
Not sure which chip but a chip looked the same as in picture (looked fried)
I tried charging it for a day,green light was on all the time.
So for a £5 I thought I would give it ago and replaced battery.
And it turned on and charges ok now.

 

[Andy_P]

Well I reckon SOMETHING can't be working properly any more...

I'm pretty sure they don't put any redundant bits on that circuit board...

 

[canderson]

I was only saying No need to get on your high horse,that's what these forums are all about to help one another giving different ideas.

High horse? Don't you know when you're having your chain pulled? :bolt:

The component he's got toasted there will prevent the battery from charging properly in first place, so while I won't discount his may be old and tired, until we can get his repaired (per the photo, it's not just a sign of being overheated, it's totally shot) he shouldn't be trying to run or charge that unit. That diode plays a very important part in overvoltage protection, and we don't even yet know how that may have happened. I'd hate to see him ruin anything else so one step at a time.

Sometimes we see this diode pop as a function of a bad charger or charging cable that can be pretty quickly identified, and sometimes not. After all of the trouble to replace the part, it always seems a good idea to recommend a replacement of the car charger as well. The overvoltage that kills the diode has to have come from the power source. An inexpensive 1A USB car charger with an appropriate USB cable is fairly cheap insurance.

 

[Garygadget]

Of course something is not working properly anymore!!!!!!!!!
Otherwise he wouldn't be asking for help

 

[nizze]

Go930 - similar problem

Hi!

I borrow this thread since it seems like I have a similar problem.
I have a TomTom GO930 and a few months ago I bought a carholder made for this model.
Until now it has been OK but then I realized that the green light was off. Hm. The fuse was blown (it has permanent power when the ignition is on).
Trying the original car charger - smoke is coming out of the unit!
So I disassembled it. It's an diode called D8 that is getting hot (can fix picture if necessary). Is that a zenerdiode as well? 5.6V? Will 5.0V do?
Could the diode have been damaged due to a bad battery?
I can still turn on the unit - but not charge it.

 

[nizze]

Btw: The D5 on the other side looks (ans smells!) OK. Measured it as well, works fine.
The carhoder was also quite expensive, made in UK.
So far D8 is the only bad component here.

 

[canderson]

Am not sure what the function of D8 is on the 930 board. I'll have to scrounge up a 730 board and have a look to see if it's included on that build.

 

[nizze]

Thanks, I'd appreciate that.
D8 is located in the middle, almost at the bottom on the board hidden under the black tape covering the frame of the SD-reader. And it's on the opposite side of the D5.

 

[nizze]

OK then. Here's a picture:

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[canderson]

I've spotted it on the 730 board, but have not had time to trace out its connections. Sure wish we had schematics for these things. Location very near USB does make one wonder about function. No idea if it's a regular diode or a zener. Not one we typically see go up in smoke.

 

[nizze]

I've recently had a friend of mine to look at it and he says it's 5.6V zener.
Will replace it next week.
Googling on D8 and TomTom Go gives a few hits; some of them even comes from this forum!
https://www.tomtomforums.com/t21066-d8-fried-720-a.html

 

[canderson]

Oops. 2-1/2 years back, and then I knew what it was.

Leaves us to wonder whether, like D5, this diode is directly subject to the input voltage from the USB port (it's certainly adjacent to the connector!), and If so, the previous advice regarding replacement of the the car charger applies. Input voltage high enough to take out a 5.6V zener indicates a failure of regulation at the car charger.