The symptoms do sound like a bad battery. Have you tested the battery voltage?

The old battery I removed tests at 12vdc. The new battery tests the same.

I do know the rooms must charge at least 24 hours when a new battery is installed before it will go through a normal run cycle. If a battery is removed or goes too dead ( low voltage) the battery monitor resets and requires to be on the charger all day agian..

12 volts sounds like a dead battery bro. Roomba batteries start at 14.4 volts and go up to 17 volts when charged.

Humm, I'll leave the new battery on the charger overnight and see what happens.

Dave, Try plugging the charger directly into the side of Roomba. Attached is a response of a similar problem. It said there is charging circuit safety that some times burns out. Robot-Doc can tell more.

Help link

Ah yes the famous 1 ohm surface mount resistor (R138) that fires up the 5 volt power to the Roomba MCU. A quick test is to measure the resistance value of that resistor. If it is more than 1 ohm you can short it out and then see if the Roomba will go into charging mode. If so then replace R138.

Thanks all. Looks like I'm going to have to dig into the little guy a little deeper. I'll keep you posted.

Well, I took the Roomba all apart looking for the circuit board and tested R138. I get 1.2 ohms so it looks good. Just for kicks I jumped this resistor with the charger plugged into the side of the Roomba. Nothing, still dead.

I have all the wheel and brush units pulled out. Does this matter? Do they have to be installed for the charging pulse to start?

Any other ideas? if not is there any place that repairs these little guys or is it even worth it?

The only plug that is needed for charging is the one from the dc charging jack that must be plugged in the main board. It is also nice to have the speaker plugged in but not a must have.

Has the power supply output voltage (22.5 vdc) been verified with your volt meter ?

When plugged into the side of the Roomba do any LEDs turn on at all ?

Remove the battery and then plug the PSU into the side of your Roomba, any LEDs light up ?

Hi Robot-Doc, Thanks for working with me on this. Much appreciated!

With the PSU plugged into the side of Roomba I'm getting 22.5 at J3 where it's attached to the board.

No light at all when I plug in the PSU, not even a flicker. Same with the battery out of the unit. No lights.

Not a lot is known about the dc-dc buck converter components that provide 5 vdc to the MCU. You will be better off getting a ebay 530 PCB and replace your board.

Thanks Robot-Doc. I kinda felt this would end up with me getting a new board.

I didn't know there were so many replacement board for sale though. Looks like a easy replacement process. However I'm a little confused on which board to get. I found a board that says:

"New 630 PCB Circuit Board Fits 510 thru 540 & 585. 620 & 630 REV 8" 630 PCB Riv 8

Then there's a basic 530 that says:

"Roomba 530 Main PCB circuit mother board NEW - 530 510" 530 PCB

Is there really any difference and which would you suggest? Would the newer ver board be a better choice?

There were some additional hardware changes to the 600 models so those boards might not fit in your 531 and some connectors my be different. Your 531 is a basic board with charging plates in the bottom to use with a home base. The 530 board that you show the link to will work in your 531. At the front you can see a black binocular shaped plastic component. That part is used to locate the home base so you're good to go with that one.

One other point, there was no major firmware change in the 600 models so you wouldn't gain any new or better features or functions with a 600 board even if it did fit.

Thanks Doc! Your the best! Off to eBay I go!

Just to wrap this OT thread up, I received a new PCB circuit board yesterday I got from eBay and installed it. A very easy swap once I figured out how to remove Roomba"s shell. After a few hours of battery charging the little guy is happily running around the house and hungerly eating up all the dirt that can be found!

Thanks again!

Great news @Dave Schulpius, glad that Roomba is up and running.

Take a peek at this Dirt Dog hunting turkeys.

Ah Ha! Sweet! I love it. Cool looking head peace. Is that a towing hitch on the back?

Ha HA, looks like a towing hitch but is in fact a volume control switch connected to a 5 watt mini amp.

Cleaver! Nicely done.

This is a great thread Dave. I too have a roomba that died that someone gave me and have been looking at making it an EZ-Robot. I figure I will be going thru the same troubleshooting you just did to get it moving.

Bret

Bret, Good to hear from you again!

The replacement of the CPU board is super easy. It cost me about $75 when all was said and done.

If it's just the resistor that's bad then the little guy is surface mounted. I thought it would be a real bugger to replace it but after watching a few Youtube vids it doesn't look too bad. The link provided earlier in this thread gives a few resources of where to buy a new resistor and what to get.

Here's a good vid on working with Surface mounted soldering:

Alright, so I apologizes for bringing an old thread back. However, my resistor on R138 has blown in half and I don't where or what to get. Could someone please post a link or point me in the correct direction for this little guy. Any and all help is very much appreciated.