Scheduler Homebase problem

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Scheduler Homebase problem

Postby d2a » December 2nd, 2017, 2:09 am

My trusty old roomba Disco is still happily chugging away but recently noticed it no longer charges on the homebase. Specifically, it detects the HB, parks up and all lights on HB are lit. The charging sequence appears to start on the roomba, and eventually the power light goes green. but when set off to clean, the light switches red and the robot does a u-turn and parks on the base again. Charging directly via the socket on the roomba works fine and it will run for around an hour. I've cleaned the contacts and checked the homebase for obvious damage, but the fact is the roomba thinks it's getting charged, even when it's not, so not sure where to point the finger. I'm reasonably technical so if further diagnostic tests can help, please let me know and i'll do em. Thanks in advance for any ideas...
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Re: Scheduler Homebase problem

Postby mfortuna » December 2nd, 2017, 9:06 am

You should try measuring the voltage on the homebase pads which is easy if you remove the front bumper. There is a schematic around that I can't find right now that shows the charging circuit. The roomba may detect the homebase voltage directly but the voltage to the charging circuit goes through a diode that effectively ORs the voltage from the jack and dock. The jack has its own diode. It is possible the dock diode is bad. I have a circuit board. D30 is the dock diode and D32 is the side jack diode. It is possible D30 is bad. If you pull the circuit board you will see two large diodes in the lower right corner (jacks facing up).
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Re: Scheduler Homebase problem

Postby mfortuna » December 2nd, 2017, 9:18 am

I found the schematic still on RR.
download/file.php?id=1858&mode=view

The MCU reads the jack voltage directly which makes sense because you don't want to start cleaning with the charger plugged in. The dock voltage is the OR'd voltage measured after the diodes. D30 could still be bad in that it passes enough current to provide a voltage the MCU can read but not enough current to charge the battery.
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Re: Scheduler Homebase problem

Postby d2a » December 4th, 2017, 5:05 am

Thanks. I think I have that straight - I'll crack open the roomba and take a look. Will try to take photos so I can confirm I'm in the right spot...
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Re: Scheduler Homebase problem

Postby d2a » December 4th, 2017, 6:58 am

OK - just diode tested the two diodes. Both seem to check out fine - ~0.52V drop across each. So now I'm stumped...
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Re: Scheduler Homebase problem

Postby mfortuna » December 5th, 2017, 8:56 am

Measure the voltage on the cathode while the robot is on the dock. You can also plug in the side charger and compare the two voltages. The dock will be a little lower but not by much.
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Re: Scheduler Homebase problem

Postby d2a » December 5th, 2017, 11:24 am

OK - I assume you mean cathode of each diode whilst connected? I'll check.

I've just tested the voltage at the dock terminals (removed the bumper as suggested and testing across the roomba dock terminals),and the voltage from the dock is slowly dropping from ~20V, around 1v per minute. Presumably this is standard charging behaviour...

Then i removed the top cover, plugged in the charger direct in the side connector, and tested the voltage between the negative dock contact and the cathode of each diode. both read the same - 20V. I then checked the same points whilst connected via the dock - same result.

Let me know if that was what you meant me to test :)
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Re: Scheduler Homebase problem

Postby d2a » December 5th, 2017, 11:28 am

p.s. i was testing at the two pins on the backside of the PCB, below where the black bumper sensor assembly is. I'm pretty sure they're the cathodes of D30 and D32...
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Re: Scheduler Homebase problem

Postby mfortuna » December 5th, 2017, 8:32 pm

The cathodes should be connected together. I think the dock voltage should be constant. Does the cathode voltage drop both when connected to the dock and side jack (not at the same time). As I recall from debugging the charging circuit the two MOSFETs operate in PWM to supply voltage and current to the battery. The voltage at the source should be constant.
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Re: Scheduler Homebase problem

Postby d2a » December 6th, 2017, 1:42 pm

Just checked - both charging methods show dropping voltage. I assumed this would be because the roomba is reporting a full charge. I need to confirm that direct charging still works, so I'm going to put the roomba back together, reset and fully charge via side port. thanks for your help so far.
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