GO920 burned out component - help identify

[Shurik]

Hi,

My girlfriend's TomTom Go920 burned out while in use and I thought I'd have a go at repairing it. Taking it apart, immediately brought my eye (and my nose) to the problem - a burned out component. The problem is - I don't know what it is.

It looks like it's a resistor R117 but it seems to be polarised so not sure if it is one. Could either be a diode or a capacitor - I am not that good with SM components. On top are markings "470 6h".

I've attached the image with the failed component (PCB picture stolen from the web). What is it, where can I get it (or equivalents) and what other components would I be wise to change around this area?

Thanks
Alex

 

[canderson]

The component you circled is a 470uF capacitor (polarized, as you noted). However, I'm surprised you identified that. FAR more common is the smoking of the immediate neighbor to the north, D5, which is a 5.6V zener (cathode end 'down', towards your capacitor).

 

[canderson]

I should note that there seems to be a fairly strong correlation between smoked D5 parts and defective car chargers. If you decide for whatever reason that it's D5, be sure to replace the car charger, too.

 

[Shurik]

Thanks for the reply. Nope, the D5 zenner diode seems OK. It's this capacitor that burned out and basically crumbled to pieces. See attached image - I literally touched it and fell apart. Everything around it looks black from soot but, presumably, undamaged.

If I replace this capacitor, is it worth replacing the zenner as well? What is the voltage rating on the capacitor and can I replace it with any standard one or does it have to be some special type?

 

[canderson]

Yikes! Yes, that one is toast. Or WAS toast. Now it's not much of anything!

Given that D5 'feeds' C133, and given that a dead D5 is most often the source of problems due to an over-voltage condition from the charger, I would recommend replacing both components together, along with the car charger. It's hard to kill a cap like that without exceeding its working voltage considerably, or hitting it with considerable reverse voltage.

 

[Shurik]

Sounds good. What is the capacitor's voltage rating and zener's wattage? I will order some SMD ones then and hope for the best!

 

[canderson]

Sadly, no idea on either. No specs on these parts other than what we have at one time or another been able to see or measure. To be safe, I would source the largest of both that will fit within the pad footprint on the board.

And don't forget the car charger! For whatever reason, TomTom thought it necessary to add a remote sense wire to the charger. The purpose of this is to observe the actual voltage being delivered at the device, irrespective of the current. Normally, this is to account for voltage drop due to the combination of wire gauge and current requirement. I'm still surprised that they found it necessary, but .... Anyway, if the remote sense wire in the cable opens, which has been known to happen, the returned voltage on that wire to the charger is (obviously) zero, and the charger starts to crank up its output voltage. From what we've been able to gather, that's limited only by the voltage the vehicle is supplying to the charger less whatever drop there is through the charger's circuit! D5 gets offended by this.

 

[Shurik]

What a stupid design!

Zener has B2E1 written on it, which, according to data sheets is:

600mA 400PIV 1uA = 2.6W? Or 3.36W if it's a 5.6V. So a 3W zener diode should do.

SMD capacitors seem to all be 6.3V... so I guess I'll get these two

 

[canderson]

Like you, I have never been able to sort out the story on the markings on D5. What you are seeing from data sheets with the "B2E1" designation is an ordinary diode with a 400V rating - more or less the SMT equivalent to a 1N4004. Kinda nuts for this application. Everywhere that we have seen anyone successfully identify what this diode actually does, they keep coming back with 5.6V zener. A recommended replacement I've seen follows:

http://www.digikey.com/scripts/dksearch/dksus.dll?vendor=0&keywords=SM2T6V8A

In the UK, you might try here

http://uk.farnell.com/stmicroelectronics/sm2t6v8a/transil-200w-unidirect-do-216aa/dp/1749297RL

If you can find on there, the Rohm EDZ5.6B has also been used with good results.

 

[Shurik]

Whoohoo! Fixed

Bought these two components: eBay items 260963833789 (zener) and 300631407609 (cap)

Soldered them in, gingerly and wonky, but as soon as I connected the USB cable, the green light came on followed by the "tadadadam" sound as it switched itself on!

Many, many thanks canderson for your advice!

Just need to get a new battery while it's still in pieces.

Also, you mentioned getting a new car charger. I have a bog standard cigarette-lighter-come-USB port in my car and a standard USB cable. Will this work OK or do you think I still need to get a "proper" TomTom charger?

 

[Shurik]

By the way, the zeners came in a pack of 10 so if anyone needs some, let me know.

 

[canderson]

Very glad to hear you found the parts and were successful in the transplant surgery.

Your 'bog standard' cig adapter will do fine if it's got a decent current rating. We recommend something at 1A or more. Much less than that and it takes an eon to charge a unit while it's also operating it.

I am concerned that your unit failure MAY have been caused by your old TomTom charger. It wouldn't be the first time we've seen it. So I'd definitely retire that one as suspect.