EM806 overvoltage

[Doddy]

Erm.... the EM806 is rated to 72V according to the Leadshine documents..



Unless you have the higher voltage 806-AC flavour?, assuming this is the case...

Damp could be an issue - if it is silly damp. Not too unrealistic in these hot humid days with the old cats and dogs lashing down.

What I've read of the EM806 is that the Overvoltage alarm...

Over-voltage Protection

When power supply voltage exceeds the limit, protection will be activated and red LED will blink twice within each periodic time.

I would expect... guess even... (and I can't overstate this enough, it's purely guesswork, though perhaps educated guesswork) that onboard there'll be a potential divider across the supply lines (possibly after onboard protection - thermal fuse or similar) - a couple of resistors, probably surface mount, that provide a feed into the onboard ADC on the microcontroller. That's what I'd do. If the resistor pairing is misbalanced - unlikely, or more likely there's a dry joint on the low-side resistor then you could end up with a high sense voltage feeding the ADC input and a spurious alarm trigger. Pure speculation, if I've not said already. There's a risk then that, depending upon the resistor values chosen for the potential divider, that this could trash the input clamp diode on the microcontroller and knacker the device (I'd say that's possible/probable given the high voltage supply on these, but - to be honest - devices often surprise me with their resilience). Solution here is to examine and rectify the potential divider, or to remove (remove the protection) and clamp the input to ground.

Or it could be an internal fault on the micro controller. In which case all bets are off.

If drying the device doesn't work then I'd be thinking not-serviceable, and plan to scrap and replace, to be honest.

Me?, I'd strip it down and eyeball it. Test it on a substantially lower supply - if it's still over-voltage with a 24v supply then there's definately a failure that needs fault-finding. Then I'd be looking at resistor pairings on board near the micro, get a microscope on that lot (likely to be small SMDs) and take it from there.

I'd happily offer an eyeball without any promise of success to repair. I do have the gear, even if no idea, to repair if the above holds true. If, however, the micro is damaged then you're pissing in the wind - you're not going to get the firmware to blow into a replacement micro. Your call on how much to throw into postage costs on a potentially (and I'd say probably) damaged board.