TomTom Go Live 825 - Device Too Warm?

[Shurik]

Hi,

My girlfriend's 825 is experiencing some issues with charging - in that it won't. Every time you plug it in, it just says "Charging paused - device too warm". It doesn't matter how cold it is (outside ambient temperature is about +5C), it always says that. It does it from the cigarette lighter socket as well as from a PC.

Software is from 12th Sept 2013 (at least that's what it say in the "about my device" screen) and it *may* have started after the update.

Any ideas? Can I revert back to old software somehow?

Thanks
Alex

 

[canderson]

It sounds as though the internal thermistor is misreading the temperature inside the case.

Yes, this information has been being displayed since the update you referenced. Before, there was no warning when no charging was occurring due to min/max temperature issues.

Q: If the unit is disconnected from external power, how long will it run?

 

[Shurik]

Q: If the unit is disconnected from external power, how long will it run?

It won't - there's very little battery juice left.

Do you have a location of this thermister? I can either replace it or put some sort of resistor to "fool" the OS into thinking it has a good temperature. I guess I could unsolder it and test it with a meter (I assume it's the resistance that changes?) ... but need to know the location of it on the board

 

[canderson]

I haven't opened up an 825 to see what the board looks like (we don't have those here in North America, nor do we have the Via 125 equivalent). Perhaps we'll get very lucky and someone else here on the UK side of the ocean will be able to contribute something.

Another question -- even after sitting in a good ambient, does the message pop up immediately upon connection to external power? I just want to assure that the thermistor is in error, and not that things aren't really getting hot in there fairly quickly.

Because these devices are prone to being used on hot windshields and dashboards, there has always been an upper limit set of something on the order of 40-45ºC for charging. Lithium ion cells do not do well above that temperature when charging. There is also a low limit somewhere around 0ºC that should kick in. So the use of the thermistor will likely be important in the future, and 'fooling' it by installation of a fixed resistor is probably not a good idea. Further, you can't remove it to leave an 'open' or it will look ice cold, and you can't short across it or it will look blazing hot, and either event will be seen as out of range and will prevent charging.

 

[Shurik]

Another question -- even after sitting in a good ambient, does the message pop up immediately upon connection to external power? I just want to assure that the thermistor is in error, and not that things aren't really getting hot in there fairly quickly.

Yep, been inside a warm house all day - just plugged it in and the first thing it said is that the device is too warm! I'll try taking it apart and seeing what's what... Will post a pic - maybe someone can ID the thermistor?

 

[Shurik]

Right, well, took it all apart and found what looks like an SMD thermistor (arrowed). But... this is a guess. There could be a thermistor inside the batter pack.



Odd thing now, though, is after putting it all together, the message isn't coming up any more and it was saying "Charging" in the battery status screen for a few minutes. After that, it's stopped charging but device too warm isn't coming up still. Any ideas? It seems pathetic that a device, which is just out of its warranty period has failed in this way. It has *one* job to do....

 

[canderson]

What was the designator on the silk screen near the component you identified with the arrow? I honestly don't know whether the 3rd battery wire on the more recent units is a thermistor output, a current sense wire, or a half voltage tap. Take a meter vs. ground to the 'extra' wire with the unit running and see if it's something like a solid 1.8V (give or take) or something else. I have also not opened a pack from one of these new units. I save that exercise for when I am replacing a battery, and apart from a few early 1xxx and 2xxx units, haven't done one since the x30 days.

To be fair, the thing has a whole host of things to do -- getting your battery properly charged being just one of them.

 

[Shurik]

I'll play around with the meter. What's a "silk screen"? The green part? There's not much on or around it. Just S1 and S2 next to nearby connectors.

 

[canderson]

The silk screen is the 'board layer' with all of the part numbers (painted on) such as D3, R126, etc.

 

[Shurik]

That's the thing - there are very few markings around. Just S1 and S2 being the nearest ones.

I don't suppose there a circuit diagram/schematic knocking about somewhere...?

 

[canderson]

Oh, I WISH! A very long time ago, we used to be able to see a schematic on the FCC site, but not in a very long time. Still, I think it's worth having a look at the three wire battery system to see what things look like with a meter there. It's a big IF, but if something looks really amiss there, a new battery isn't typically that difficult do deal with.

 

[Shurik]

Still haven't had a chance to take apart the unit again but I am pretty sure that this SMD component IS the thermistor. I am aching to replace it but I need to know what value the thermistor is. Fitting the wrong thermistor will give the unit wrong "range" of temperatures and thus break the battery.. Any way to ID it? Measuring it might be moot if it's faulty.

 

[canderson]

You're right about the issue of getting the right value. Are there ANY markings on the component itself that you can identify? Apart from that, we'd need someone to open up an 825 and get at least two values at two spread temperatures to give us something to go by.