Frustrated... battery or dead roomba?

[s_mack]

My Roomba 4XX (not sure) Scheduler worked fine for years. The original battery finally died... or so I figured. I got a new battery off eBay (said "genuine") and it worked for no more than a week (maybe 3 cleans) and it was dead. So I bit the bullet and bought another new battery locally for $80. I charged it for about 3 days. I'm sure at one point it did show green, but this morning I noticed it was blinking red again. Hit the "power" button and it does NOTHING... no beep, nothing. None of the buttons do anything. The ONLY thing I can get the Roomba to do is blink red while plugged into the charger.

With a multimeter, I looked at the battery and it shows only around 2.45V. The charger seems fine as it puts out 22V as expected. I disassembled the roomba somewhat and tested the plugin where the charger goes to see if that was damaged, but no... the circuit board is getting the 22V. I'm not sure if its normal or not, but the charging tabs (that contact the battery when it is inserted) only show 5V. I would have thought that would be 22V too, but I have no idea what the circuitry in between is doing so 5V may very well be the proper voltage.

Any ideas on what I can do? I can accept that my Roomba is dead... what sucks is I just shelled out for a brand new battery. Store won't return it, which sucks. I can't see how I managed to get two dud batteries in a row.

- Steven

[vic7767]

There are two devices on the Printed Circuit Board that may have failed. Do a search for "U2 U4" in this forum and read about others that have had the same condition and what was done to resolve it.

[s_mack]

Ok... real stupid question I'm sure.... but how do I search? I tried that in the "advanced search", with and without quotes, and I get this:

The following words in your search query were ignored because they are too common words: u2 u4. You must specify at least one word to search for. Each word must consist of at least 3 characters and must not contain more than 14 characters excluding wildcards.

[vic7767]

try searching using this string U2 U4 MOSFET

[s_mack]

I searched via Google and found some discussions on other sites that appear to be on the right track, so thank you very much for the tip!

Could I bother you for another? I think to rule out the battery I should see if I can charge it externally and if the Roomba then works. If yes, then that probably means its the charging circuit and I can tackle that. If not, then its something else (Roomba is $@#ed or batteries are all no good). But I don't want to buy a rapid charger just for this. I am NOT an electronics guy at all... is there a simple way I can go about charging my battery "manually"? Someone on one of the sites I just read mentions doing it with a car battery, but I'd need to be hand held for that (exactly how would I connect and how do I know when its done??)

Either way, thanks for your help thus far.

[Gordon]

... I'm not sure if its normal or not, but the charging tabs (that contact the battery when it is inserted) only show 5V. I would have thought that would be 22V too, but I have no idea what the circuitry in between is doing so 5V may very well be the proper voltage. ...

I presume you are referring to the Home Base contacts. If so, be aware that voltage is held low (and impedance high) until the HB is satisfied that a proper Roomba has contacted the HB, then it up-switches voltage and delivers charging current to the robot.

[TechGuy]

You can charge the battery directly using Roomba charger - Charger +ve to battery +ve and charger -ve to battery -ve. Charge only 15 min. Charging too long may damage the battery without the overheat shutoff protection. Please do not leave the charger and battery unattended during the 15 minutes.

If your battery runs your Roomba longer than a few seconds(wrong) after 15 minutes charge, your battery is good. The U2 and U4 MOSFETs on your Roomba have failed.

Update: If your battery runs your Roomba for a few minutes, your battery is good. Sorry for the wrong information.

[s_mack]

I presume you are referring to the Home Base contacts.

Actually, no. I mean the contacts in the roomba's battery compartment with the battery out an the charger plugged in directly to the roomba. I was trying to see if the voltage was getting through to the battery.

[s_mack]

You can charge the battery directly using Roomba charger[...]

Thanks so much! That picture is amazingly helpful. Really appreciate it.

[s_mack]

I'm charging now! hopefully it works.

Curious though... why would the light have gone green and THEN go dead? I guess I"m just wondering if the mosfets were dead, that it would have never been able to charge to green at all, right? Unless they died during that charge... but then would a system with bad mosfets completely discharge the battery while in the charger for a couple days? And if it just died during that charge, then was my 2nd battery (that only lasted a couple charges) really bad?

Random thoughts. Quasi-rhetorical, I suppose, because I think you have no way of answering without more info.

FYI. The battery I'm manually charging at the moment is the 2nd (previously presumed bad) battery, not the brand new one.

[s_mack]

OK, so my batteries clearly aren't the problem! Good, on the one hand... at least now I know. Sucks that I've wasted my money on one (maybe two) batteries for no reason

Alright, so now to tackle this mosfet issue. I'll read more up on it and try to figure out if its something I can handle, or if I should just buy a mainboard. I found one for $40 and I suppose that's not too bad. The mosfets are really small and my solder skills are pretty rusty (and poor to begin with)

Alternatively, I suppose I could get an external charger. Amazon had one but not in stock.

- Steven

[Gordon]

... I mean the contacts in the roomba's battery compartment with the battery out an the charger plugged in directly to the roomba. I was trying to see if the voltage was getting through to the battery.

In that case, you should expect these data:

a) No voltage to appear between V_pos & V_neg (the two connector blades (pins) on the chassis connector). Roomba will not switch charging power through to the battery when no battery is present.

b) +5 volts should be measured on the chassis-connector's side-button contact, relative to the V_neg pin (which is the one closest to the cell-pack in the battery case. That five volts is used to provide bias current to the thermistor inside the battery.

If you can read schematic diagrams, then seek schematic1 and review its information about the (orange colored) charging control circuit.

[Gordon]

...Alright, so now to tackle this mosfet issue. I'll read more up on it and try to figure out if its something I can handle, or if I should just buy a mainboard. I found one for $40 and I suppose that's not too bad. The mosfets are really small and my solder skills are pretty rusty ...

You must do the same disassemby / reassembly work either way. IOW, R&R using a replacement board will be much easier / faster, BUT, BE SURE TO NOT GET CONNECTORS CROSS-CONNECTED, ELSE YOU MAY NEED ANOTHER BOARD!!!

Alternatively, I suppose I could get an external charger. ...

An iRobot Rapid Charger on hand gives a safe re-charge (may require a double charging cycle to accomplish full charge, see here) and makes a good trouble shooting tool, however, it is not in production. Search eBay, or ask TechGuy how much he wants for the one (or more) he advertises.

[s_mack]

I can't make sense of schematics, sorry.

From another thread on this forum, I went through these diagnostics. I expected it to fail one or more of the voltage/current/trickle tests but it passed everything.

Thoughts on how that relates (or doesn't) to the mosfat issue?

- Steven

[vic7767]

Thoughts on how that relates (or doesn't) to the mosfat issue?

When the MOSFETs are defective the internal diagnostics does not discover the failure.

[Gordon]

...From ...another thread on this forum..., I went through ... diagnostics... . I expected it to fail one or more of the voltage/current/trickle tests but it passed everything. ...

We have learned quite a lot since the time of that old thread, but we will never know everything we'd like to about the charging-control process. I would suggest repeating Tests-15 & -16, but don't depend on the routine to tell you about pass or fail, use your hand on the battery, this way:

1) Step into Test-15 (BTW, did you notice you can reach the higher numbered tests by reverse traveling via the SPOT button?!), and after plugging in the PSU's dc-cable let Roomba remain in -15 for about half an hour. Put your hand on the battery at that time to determine if it feels warmer than it was when you started Test-15. If warmer, the implication is both charging FETs are passing current before they have been commanded ON -- if so, they are kaput, or their driver xstrs are stuck ON (not likely, but would require lab testing to find out). Probably, the battery will still be at room temperature.

2) Next, step to Test-16. Roomba will command high-rate charging to begin. Again, you will have to wait for time to pass before the cells heat, and that heat flows to the battery-case wall, so, give it at least another half hour, followed by feeling the battery case for warmth. If the case is as cool as when you started, one or both MOSFETs have not switched closed, hence no charging current. If so, one or both FETs are kaput, or one or both of their driver xstrs are stuck OFF (not likely, but would require lab testing to find out).

Disconnect the PSU, and pull the battery to end testing.

Of course those tests depend on the PSU working properly. To confirm that a no-current result from Test-16 actually means failed FETs, you must load-test the PSU using some dc-resistance that will draw one ampere, or a little more, from the PSU.

[s_mack]

Wouldn't the PSU be OK if I was able to manually charge the batteries as per earlier suggestion?

I'll do the tests as you indicated, thanks.

[s_mack]

Thought occured to me: has anyone found someone selling upgraded boards with higher amp mosfets? Because if I understand correctly, I'm likely to cook the new ones just as easily, simply by charging a really discharged battery, right? However I fix this (soldering new fets or buying a board) I'd rather not just do it again and again.

[TechGuy]

You can use STD10PF06T4 as described in this page --> http://home.comcast.net/~davidtief/room ... grade.html

The problem, that you may encounter, is finding it. No body carries this MOSFET. Special order is 3 - 6 months.

[s_mack]

Well yeah, that is a problem.

OK so riddle me this... assuming its the fets.... what should I do? What would you do? What do people do?