Fixing a faulty Roomba charger

An ongoing saga, seeing as I’ve not fixed it yet…

The story so far..

Our Roomba (a old 533 pet series) stopped charging after a particularly nasty lightning storm and blackout – some initial testing, and guess work, narrowed the problem down to the charger and thankfully not the Roomba itself.

Being an optimist who hates just “buying another one”, I opened the now naff charger (charger model 17062, PCB STS-IRO-120-R3F-AG).

https://upload.wikimedia.org/wikipedia/commons/b/bd/TOP_STS-IRO-120-R3F-AG.jpg
I’ve made this available on Wikimedia Commons 💜

I assumed the issue was just going to be a dead fuse. I was half right.

Something had gone bang

Image
It’s not meant to look like that, honest.

It was immediately obvious the charger had experienced a pretty nasty surge on the incoming supply, evident by the less than ideal state of RV1 (a rather crispy metal oxide varistor) – it was so charred I could only see the end of the component’s markings, “471K”.

Some Googling turned up a datasheet for a 07D271K, which thankfully gave a part number explanation:

But seeing as I’m lazy (and have a surge protected power strip), I opted to remove RV1 entirely, crossed my fingers and powered it up.

If only it were that simple..

No dice, still wasn’t getting the expected 22.5VDC out the barrel jack and the green LED was not – I went back to buzzing out the board with a multimeter and found F1 was dead.

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Yes the mains connection being so loose is triggering me too..

That slightly melted red thing is a 3.?A, 250V fuse – the fact I couldn’t read the amperage was kinda annoying, but a helpful forum thread about modding the charger for “fast charging” leads me to believe its probably a 3.25A radial time-delay fuse.

Now obviously I don’t have one of these laying around (not to mention that randomly taking things to bits to find one probably wouldn’t go down too well…), and I’m not too keen on shorting it out even temporarily (mainly because I don’t know if the rest of the board is good or not yet..) – so I guess its time to see how quickly RS can deliver..

Until next time…

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