Need Help Identifying Part

Guess what I acquired :) It sings and vacuums and is a robot :P Roomba! It's a first gen (I think), but it was cheaper than a new battery - and it came with a new (in box) battery :P

The problem came when I went to charge it. At first I thought it was fully charged - and the battery acted like it was (1 hour+ of runtime on carpet). But now, it won't charge.

Skip ahead some time.

I've narrowed it down to this component (see image). When I spray it with canned air liquid - the charger comes back to life. Not to mention, it looks scorched.

I'm fairly certain it's a tantalum capacitor. Except, the PCB marks it as "F1" while other tantcaps are "C#" designated. Can anyone confirm/identify?

Oh -- it's currently charging with the charge cct in the refrigerator. I'm using a Kill-o-watt to see if it overheats (current drops off) :P I'll be modifying the case with a cooling fan once I've replaced the component :)

I've got to say though -- it's really fun to watch is honestly pretty effective and getting stuff out of our "clean" floor :P

Picture of Need Help Identifying Part
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westfw10 years ago
It should be easy to distinguish polyfuse from surge supressor, at least. If it's a polyfuse, it will be in series with the supply line somehow. If it's a supressor, it will probably connect between the supply line and ground.
LasVegas10 years ago
Try removing it. If the charger works okay with the component removed, it was a varistor. This is the same components you find in most power supplies and surge suppressors. Its purpose is to absorb spikes coming from the mains. It looks like yours would be a smaller one than you'd find in a surge suppressor since you're working with 24V. I'd look for a varistor rated at about 50 volts. Check the part number on the component if you can.
trebuchet03 (author)  LasVegas10 years ago

The other side says


My concern with removing a surge suppressor is that these robots are already extremely sensitive to power spikes and brownouts... Maybe this is the bad component causing problems for others :P

Thanks :)
I don't mean to remove it permanently. Just to see if the power supply operates without it. If there is power with it removed, it would confirm that it's a Varistor. If it fails, temporarily, short it and test. If the power is then available, Westfw was right and it's a Polyfuse.

These are just tests to determine the problem and the unit should not be used without the component. Once you've confirmed which it is, get the replacement component.

If it's a polyfuse, look on the power supply unit itself for it's power rating (Watts) or current (Amps). If you found Watts, divide it by 12 to get the current (IE: 45W / 12V = 3.75A ) Add about 20% to the current (IE: 3.75 * 1.2 = 4.5) to determine the approximate current rating of the fuse you need. In the above examples, I would choose a 12V, 5A fuse.
trebuchet03 (author)  LasVegas10 years ago
Gotcha - thanks :) I'll be testing it later. I'm thinking it is indeed a polyfuse just by inspection of the casing and circuit - it connects to the power input and to some of the first pins on IC1. Couldn't I just test resistance? If it's a fuse, it should have almost no resistance. If it's a varistor, there should be something there right? I just want to avoid releasing the ever so magical smoke from unmarked components :P Anyway, the charger is 24V @ 500mA - so I'd need a ~600mA fuse should it be a fuse :P
If it is a polyfuse, you could replace it with a regular fuse. Just plan on replacing it any time it blows. A Varistor will indicate almost infinite resistance if good and a short if bad. I'm guessing from the part number that the original was 500mA, which might explain why it burned out! Yes. I'd replace it with a 600mA fuse.
trebuchet03 (author)  LasVegas10 years ago
Oh, I forgot to mention --- this thing doesn't get mains power -- it's getting 24V from a wall wort :P
i swear on my life and my mothers life and god and buddah and my dads life and my sisters life and even,yes, my soldering iron that u, lasvegas, know EVERYTHING!!!!!!
westfw10 years ago
With a label like F1, I'm betting it's one of those self-resetting "polyfuse" devices; like a fuse, but should turn back on when it cools down. one Vendor here. It could have gone bad somehow, but when a device keeps tripping its fuse that is usually not a good sign :-(
trebuchet03 (author)  westfw10 years ago
Thanks :) When I opened the case, that component was stuck against one of the case walls -- not very good for heat dissipation should it need it. It's been in the refrigerator for for almost 10 hours now and it hasn't tripped (yet?). It's also cool to the touch. I guess it's time to start experimenting :P