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Q&A

How can I debug, (and eventually fix) this Roomba PCB? [closed]

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Closed as off topic by Nick Alexeev‭ on Dec 10, 2020 at 19:21

This question is not within the scope of Electrical Engineering.

This question was closed; new answers can no longer be added. Users with the reopen privilege may vote to reopen this question if it has been improved or closed incorrectly.

I've got a broken roomba, I've tried new batteries and a working charger.

The charger is supposed to output 20V-24W when the roomba is plugged in.

the picture just shows how I'm measuring the power taken from the charger. I bought a Power Meter for this purpose. A functional roomba shows between 20-24W when the battery is charging, but mine shows between 0.8W-1.6W when the problem roomba is supposed to be charging.

voltage reading

My multi meter shows no connection from positive to positive pcb -> charger connector, but someone told me I could be seeing strange readings due to the Charging Mosfets. So now I'm stumped on how to continue debugging this. There is detected connection from Negative -> Negative.

Continuity tests on the PCB -> charger

Multimeter shows no connection positive -> positive

PCB Side 1

PCB side 1

PCB Side 2

PCB side 2

Additional info:
For testing I've disconnected everything except the Battery -> PCB and connector for PCB -> Charger.
The charger has 2 metal plates that attach to the roomba's 2 metal plates.
The Roomba was working at one time. I only know this based on the amount of dirt inside the roomba.
There is no issue with the charger or the battery. Both have tested in a working roomba
The roomba (model 690) uses a 14.4V Lithium Battery

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6 comments

I don't know how the Roomba charging circuitry is designed, but it's not at all unreasonable, particularly in consumer electronics, to not have direct DC connectivity between a charger's output side and a built-in battery. If it uses a lithium-based battery chemistry (a good guess in today's world, though I don't know), then all the more so. Canina‭ about 1 month ago

@canina it IS a lithium battery, the older models used nimh, but this one uses Lithium (690). Unfortunately there's no way to get a hold of the schematic as there's no way irobot would provide it. dustytrash‭ about 1 month ago

@dustytrash Even if you had access to a full and accurate schematic, that looks a whole lot like a multi-layer PCB to me, and it's definitely packed with surface-mount components including delicate ICs. Even if you had the knowledge, that's not something you "fix" with tools even most electronics enthusiasts would be likely to have at home; let alone if you had to go buy a power meter to determine the current draw of the charger, and are stumped once someone talks about power MOSFETs. Sorry. Canina‭ about 1 month ago

This post is discussed on meta here. Lundin‭ about 1 month ago

PCB side 2 shows a lot of signs of a poor solder job. Check the top right corner of the last pic for example (looks like 0402). Probably they configured the placement machine poorly - there's too much solder everywhere and the potential for shorts looks extensive. Get some dirt on the board and anything can happen. Lundin‭ about 1 month ago

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1 answer

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The charger is supposed to output 20V-24V when the roomba is plugged in. However it's only showing 1.6V.

If this is really true, then there is no point going further. The charger isn't working, the Roomba got discharged, and now wont run because it can't be recharged.

However, it's not clear what is really going on. You say:

the picture just shows how I'm measuring the voltage. It's 0.4 when roomba is disconnected, 1.6V when connected.

But the picture seems to show something completely different:

Image

There are a number of issues here:

  1. You haven't explained what that black thing is you're holding, or what its relevance is, so we can only ignore it.
  2. Your original picture is huge and shows a lot of blank wall. Learn about "relevance", and then crop pictures accordingly. There is no need to waste a full screen's area showing us the meter display.
  3. You don't show the actual connections to the charger, which would have been useful. Frankly, I'm skeptical you know how to measure the charging voltage. I need to see it to believe it.
  4. However, most importantly, you're not actually measuring voltage. This is apparently a plug-in power meter. It measures how much power something plugged in is drawing. It plugs into an AC wall outlet, and provides its own outlet to the unit under test. That lets it get between the AC power line and the unit, which allows it to measure the power drawn by the unit.

    I can't even imagine how you thought this was a voltmeter. Not only would this have been sold as a "power meter", but we can clearly see that the 0.4 you show is labeled with a "W", meaning Watts!

So apparently the charger is drawing 0.4 Watts with nothing connected, and 1.6 Watts when the Roomba is supposed to be charging. 400 mW is a little high but still plausible with nothing connected. However, 1.6 W is way too low to charge a Roomba.

Charging is definitely not working. It's impossible to tell from that whether the fault is in the charger or the Roomba, or possibly (but unlikely) both.

Frankly, someone that thinks a power meter is a voltmeter and doesn't know that "W" means Watts shouldn't be inside electric equipment like that. You're in over your head. Close everything back up and hope you didn't break it more in the process of poking around in there. There is nothing for you to see in here. Move along.

What you can do is swap parts to determine whether you need a new charger or new Roomba. Find someone with a working charger/Roomba combination. Try your charger on their known working Roomba, and vice versa. One of the combinations won't work, which tells you which of your units is broken. Then go buy a replacement.

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2 comments

My mistake on the power meter, I'll update my post to make it clear my working charger shows between 20-24 when connected to a working Roomba, but exactly 1.6 when connected to my not-charging roomba. dustytrash‭ about 1 month ago

@dust: Then you have a broken Roomba. Get a new one. This is not something you can fix. Olin Lathrop‭ about 1 month ago

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