Repairing a Roomba

[AjohnwParticipant @ajohnw51620]

My son bought us one of these around 18months ago. A 630 which uses NmH cells. Not sure I would want a lithium type.

It's worked well and even gets dog hairs up but started coming up with the clean battery terminals message. Sometimes it was ok but eventually it always came up with it. We had cleaned all of the terminals.

I checked the power supply and that seemed to be ok but couldn't check it under load easily without trying to attach bits of wire to things so I took it apart. Turns out to be pretty easy. There is a thin narrow skirt around the base with lots of screws. Remove and the sides can be taken off. The top is a mix of screws and clip on bits. This looks like it's worth doing every now and again to remove dust from around the inside edges of the housing anyway.

Checking the on charge voltages was easy then. 2 large pads that are even marked. It wasn't getting over 12v. The Mosfet's mentioned all over the web seem to be working as they are checked each time it charges the battery.

I then looked around for a new charger. The price was daft so ordered a 20v laptop power supply which I think should give enough volts. Currently it's happily charging with an 18.5v one we had around but that might not allow it to fully charge as 18.7 or so may be needed. What I should have ordered really was a universal one with a switch on it. They usually have a 22v setting. 1/2 volt higher than the Roomba one but ebay refused to include universal in the search and came up with over a 1000 dedicated ones.

If the Moosfets do blow they look fairly easy to replace. Snip the small leads and desolder etc. They use 3. 2 for battery charging. The other seems to provide the 5v for the circuitry.

Roomba – great but if there is a dog around it's best to run it every day. It's probably best to get one that does this itself but it's just a case of pressing a button. It vacs the room and then returns to the charging station. I get the impression that accumulated dust in the "skirt" can cause it to spend more time vacing than it needs to.

John

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[AjohnwParticipant @ajohnw51620]

Robotic vacuum cleaner

[AjohnwParticipant @ajohnw51620]

I bought a 20v laptop charger. Argggggggggg It gives charging error 2 with that shortly after it's plugged in. This seems to mean that it's spotted odd current values. It also seems that this can mean that the Romba is toast but if I put the 18.5v on back all is ok except not enough volts to completely finish a recharge – ever so close though.

Maybe there is too much ripple on the 20v supply. The actual Roomba charger puts out 21v according to it's markings. However it might really be a nmh charger in part not a power supply. That doesn't make much sense either as the 18.5v supply can put out 2.5amps. The 20v one 2 amps. The Roomba one 1.25 amps.

To be honest I am rather surprised by the shear quantity of electronics bits and pieces on the board and wonder if that is down to numpty electronics people.

John

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[AjohnwParticipant @ajohnw51620]

Just a note. If anyone else tries sorting this out it looks like the software in the Roomba is closely tied to the charger they supply.

Best option is to buy a new charger or fix the one that's broke. What seems to have happened to ours is that at times it puts out 21v and then for some reason drops to 12 – 14v while charging the battery. The Roomba seems to start some sort of timer and after 1/2 hr or so the error is reported.

I haven't got the scope out yet so have no idea if I can fix the charger. It's a curious fault that doesn't seem to be related to things heating up etc. In some respects it's a cheap and tacky unit as it uses a paxolin circuit board rather than fibre glass. It looks like it may use an opto isolator to allow the output to control the mains switching.

As it's paxolin I have run an iron over all of the joints. Only one had air / moisture trapped in it, One of the joints on the output leads which had also been badly stripped and forced into a hole. They put some sort of gunk over it though so probably ok.

John

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