Hi all,

I'm wondering if I might be able to repair the main board of my Husqvarna robot mower. It has water damage, so may be beyond repair but would like to give it a go.

What I've done so far is:
- measure voltage of battery when disconnected - 18.8V
- measure voltage of the battery when connected at the battery terminals and also at the board connector - drops to 0.9V
- measure voltage across the '100 VFK MD2' cap in the top right - 0.9V

Could anyone give some pointers on what to check next? My A-level in electronics is badly failing me.

 

Using the continuity setting on your multimeter, with the battery disconnected, measure both ways round, between each of the three connections (2 legs and tab) on the MOSFETs shown in red and report back. Looks likely that board has got very wet at some point?

It also looks like a component has gone missing (yellow)

 

Hi Irving, thanks for the quick reply. I just checked this and in every combination, multi-meter is showing an open circuit. Yeah, I think it go quite wet. Shouldn't have left the mower out in the rain over winter

 

First, board must be dried good from water damage, before attempting to connect battery
Never connect battery unless you are sure that water completely gone from the board

 

Hi Irving, thanks for the quick reply. I just checked this and in every combination, multi-meter is showing an open circuit. Yeah, I think it go quite wet. Shouldn't have left the mower out in the rain over winter

Hi, and welcome to AAC.

I updated my reply to include the other big MOSFET. Were there any bits lying around in the case?

 

Hi, and welcome to AAC.

I updated my reply to include the other big MOSFET. Were there any bits lying around in the case?

The other MOSFET is the same - open circuit with all combinations. I double checked what those two solder tabs are doing by looking at photos on the web but it’s the same - there’s nothing connected. They’re a bit scratched in the photo from when I’ve been probing them which is why it looks like something might have been there previously.

 

Hi, and welcome to AAC.

I updated my reply to include the other big MOSFET. Were there any bits lying around in the case?

Hi Irving, do you think there's anything I can try or is it a non-starter? Any input greatly appreciated!

 

Sorry, been busy... Puling the battery down to 0.9v isn't good for the battery or the other parts.That suggests a dead short across the battery. I'm assuming that's with nothing else plugged in to the board? Is the battery fully charged? How many cells in the pack - looks like it could be 5 for 21v fully charged, 18.5v on load. What are the individual cell voltages? I can see a 4-way connector to the inner 3 cells, is there a separate 2 way black/red connector for the outer 2 cells? What are the individual cell voltages when pack is disconnected and connected?