My model 550 — 500 series — Roomba has been on-and-off idle for several years. It worked for a while — at least two years ago — with a new battery. But after about a year, it died with the dreaded “ERR 3” and 3-blinks. I set it aside and have occasionally tried to get it to work. I have not been able to get it to work since — it always started with the Err3 and 3 blinks. It would go no further — a nice round black brick.
This year I decided to try again. It was firmly stuck, after staying on the charger overnight, with the Err3. I read various postings saying to clean battery and machine contact terminals, I did so. No success even after an overnight charge. Still a brick.
I’ve read several failure threads with the Err3 failure. One was about there being 2 FET transistors that controlled the charging system. If they failed, then the Roomba would be stuck on Err3. There was also an instance of a “expanded” failed electrolytic capacitor being a problem. As I was about to throw the thing in the trash, I decided that I had nothing to lose by taking it fully apart — and disassembly seemed like a good afternoon’s fun.
So I took it apart using these instructions from the RobotShop (https://www.robotshop.com/media/files/pdf/roomba-500-disassembly.pdf ). Not hard to do but takes a few minutes with lots of screws.
I examined the FETs and looked for failed electrolytic capacitors (i.e. components that were burned, bloated, charred, etc.) . No joy.
I had also read about taking out the motherboard and cleaning the whole board with isopropyl alcohol. At this point, the board was out and I had noticed some slight corrosion and dust. It was seconds away from the trash. So I took it to the sink along with a bottle of 70 percent rubbing alcohol and a toothbrush. I gave it a vigorous bath and rise. I used a hair dryer to make sure it was well dry (mainly to get the alcohol’s 30% water out).
After reassembly — which was a bit more tedious than taking it apart — I charged it overnight.
IT’S ALIVE! No Err3. Works just like new. Happy face here.
I’ve done a lot of electronics design, engineering, repair, etc. The amount of debris and/or corrosion on the motherboard was small. I’m surprised that this was the source of the problem and would cause the major Err3 hard fail. I’m also surprised that this not-inexpensive, brand-name device which is targeted for routine use in the dirty environment of a floor would be so finicky about surface debris/corrosion and that they did not include a conformal coating on the board to protect it.