tomtom go 720 not charging

Discussion in 'General TomTom Discussion' started by goofy gorilla, Jan 9, 2011.

  1. goofy gorilla

    goofy gorilla

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    hi guys - im new to this forum so hopefully you guy may shed some light on my problem...I have a tomtom go 720...use to work fine, then ocassionally i had to wiggle the usb connection about and the unit would start to charge , green light on unit would come on...now the green light doesnt come on and unit is dead...been reading that it may be a zenner diode that could have blow...ive looked at the board and cant see any lifted or cracked joints, however as you can see in the picture..this component seems to have brownish joint to the right..is this a zenner diode ?..can it be replaced ?....im not that into repairs etc...was just wondering what else it could be...cheers

    it has 768D6 written under it.....
     

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    goofy gorilla, Jan 9, 2011
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  2. goofy gorilla

    dhn Moderator

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    Moved to appropriate forum.
     
    dhn, Jan 9, 2011
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  3. goofy gorilla

    canderson Moderator

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    Before assuming anything about the zener, I'd take a look at another cable. Had the same thing happen to my 720 a while back. The USB wiggling had me concerned. Finally wouldn't make contact at all. Was confident that it was the internal connector on the unit, and even opened up the case and inspected to see if one of the contacts from the connector had lifted... but turned out to be my charger cable failing at the contacts.

    Does your unit fail to produce a green light both on the vehicle charger and the dock? Do you still have the dock handy to try? Have you tried another USB A/mini-B cable to see if that helps?
     
    canderson, Jan 9, 2011
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  4. goofy gorilla

    goofy gorilla

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    yes, ive tried different cables ,including the usb docking station..ive also tried a different car charger, its dead as a dodo...is that the zenner diode that i have marked in the pic..doesnt look too healty..i might open my other tomtom go 530 and see if it looks similar..
     
    goofy gorilla, Jan 9, 2011
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  5. goofy gorilla

    canderson Moderator

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    Do you have access to a good DVM, and would you know how to use it to check at least the open/short condition of a zener diode? It would also be interesting to know how it looks when powered - that's the only way to see if the thing actually works.

    As often as not, and I haven't looked at the traces right at the USB, but that's where this diode is, a zener will be used to either set up a particular voltage or protect a device when above a particular voltage. Not the most efficient way to do a voltage regulator for high current, though, so I'd suspect the latter, in which case it likely sits directly between power/ground. In that configuration, it will suppress high voltage spikes, but only brief ones. Prolonged exposure to more than the breakdown voltage will draw a lot of current. They'll typically take the supply fuse out in the process. If the fuse survives, though, it'll take out the zener instead -- so to start, you really do need to meter the thing for a total open/short condition. A total short condition will have either taken a power supply trace off the board or keep will blowing the fuse on the supply. If it's a zener, I'm right about what it's doing there (it's a big one, so that would make sense), and it's an open, you'd never know the difference until a voltage spike took our your unit altogether.

    This all assumes it's a zener to begin with. I was just inside a 730 day before yesterday, but only tend to focus on the problem area I'm fixing. Haven't had one of those go poof yet on anything I've opened.
     
    canderson, Jan 9, 2011
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  6. goofy gorilla

    mikealder Moderator

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    Usually when the diode gets blown it looks fried unlike the one in the picture, also with a fried diode the green LED will still illuminate with external power applied to the device, I would suspect the mini USB socket is at fault from what you have described - Mike
     
    mikealder, Jan 9, 2011
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  7. goofy gorilla

    dhn Moderator

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    I remember seeing somewhere that somebody carefully wedged the thin part of a toothpick between the usb port and the surrounding area on his unit. It stopped the wiggling of his connector and resolved the problem ... for him.

    I'm just sayin' ............... :rolleyes:
     
    dhn, Jan 9, 2011
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  8. goofy gorilla

    canderson Moderator

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    So would I (USB socket).

    Note however that if that diode shorts in the configuration I described, he won't see a green light. He'll have a dead short across the power input. Diode doesn't have to look toasted, either. If you hit it fast and consistently enough with the overvoltage (e.g., 13.8VDC), the innards can toast before the outside of the case even heats up much. Granted, I don't have specific knowledge of this component in TomTom use (and without checking, I don't even know if it's a zener), but having used them as I described in a couple of different flying lead and SMT designs, can assure from lots of post mortems that they can look perfectly healthy after the fact. A quick meter check that discloses bidirectional dead short tells the tale, though.

    Only an open would allow the unit to continue to light up. Again, a meter would give an indication of that, too, since it should conduct easily in one direction with the DVM.
     
    canderson, Jan 9, 2011
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  9. goofy gorilla

    goofy gorilla

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    ok thanks guys, havit got a DVM..might take it to a some specialist to get it checked out, probably charge me a small fortune....if too much will probably bin it. :eek:
     
    goofy gorilla, Jan 9, 2011
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  10. goofy gorilla

    canderson Moderator

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    Forget the specialist. If you have a buddy with a meter that knows which end is which, it's an easy check.
     
    canderson, Jan 9, 2011
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  11. goofy gorilla

    goofy gorilla

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    ok ...i have found out that the unit charges and works only when the its connected to usb port on a pc via the usb docking station...it does not charge or come on when connected to a home mains charger or in the car, via the car charger....:confused:
     
    goofy gorilla, Jan 10, 2011
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  12. goofy gorilla

    canderson Moderator

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    Right - that brings us back to a connection quality issue, I'm afraid. That's why I asked earlier whether "Does your unit fail to produce a green light both on the vehicle charger and the dock? Do you still have the dock handy to try?" A lot of people don't use the dock much, and the fit there often seems to stay a bit tighter.

    So now the question is whether the internal USB connector is getting so sloppy that it will only work with a select set of male connectors which, unfortunately, do not at present seem to include your car charger.

    You say you *have* tried it with another standard USB A - miniB cable plugged into the USB port on your computer, and had no luck there, either?
     
    canderson, Jan 10, 2011
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  13. goofy gorilla

    goofy gorilla

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    ok heres what i have done..i have 3 different usb docking stations....the unit will work on all if connected to usb port on pc.

    if all 3 usb docks are connected to a mains/usb plug...the unit does not work.

    tried the 3 different tomtom car chargers in the car none will work...however the car charger that came with unit works if i push the charger in very hard and hold it. this car charger is slightly diffrent from the other car chargers as it has a right angle bend in it..the other two are straight..

    hence my conclusion is that the usb port on the tomtom unit is knackerd...lol

    i only have 1 USB A - miniB cable , that cable is fine as i have tested it on several other units and works fine.
     
    Last edited: Jan 10, 2011
    goofy gorilla, Jan 10, 2011
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  14. goofy gorilla

    canderson Moderator

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    You're down to an ugly choice. You need to find someone competent to replace that USB connector on your 720 or chuck it. The connector itself isn't all that tough to find. I'm pretty sure I even spotted one at Digikey a while back. However, you need someone with a bit of skill with an appropriate soldering iron to swap it out. You don't want someone in there with a huge iron cooking the traces off the board, and that connector is soldered in there pretty well... not just the 5 small surface mount connections, but two big surface mount tabs on the sides that anchor it in place.

    Seems to me from some old notes that a Molex like this one http://www.molex.com/pdm_docs/sd/473460001_sd.pdf or similar was the ticket.
     
    canderson, Jan 11, 2011
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  15. goofy gorilla

    goofy gorilla

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    thanks...will try to find someone or sell it for parts...
     
    goofy gorilla, Jan 11, 2011
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  16. goofy gorilla

    canderson Moderator

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    Hope you can find someone who will work it out for you. If not, let me know before you bin it. Also have a 720, and while it's primo at present, you never know down the road.
     
    canderson, Jan 11, 2011
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  17. goofy gorilla

    goofy gorilla

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    ok guys..got it sorted found a bloke who sorted the usb port for me...?19 posted back...not bad lol..thankd for the help and advice...much appreciated..:)
     
    goofy gorilla, Jan 14, 2011
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