EM806 overvoltage

just powered up my router after a few months and i am getting an overvoltage alarm on one of the three drives. I have checked the wiring and all seems secure and un broken. The voltage measures as 73v dc. i have spoken to Gary at zapp automation and he said it could be broken or damp. I have taken the cover off and none of the components seem blown. Does anyone repair these drivers, or can anyone suggest what to test on them? i have taken it inside to warm it up just incase its a damp problem. Thanks all

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

Attachment 28511

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...

Quote:

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Over-voltage Protection

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

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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.

Attachment 28512 Not sure where the 72 volts came from. But here is a pic of the front of the driver where it is clearly 80v. I note that ot says in your document that it is recommended voltage so maybe that's it.

If you can find them - get a few diodes wired in series - each will drop around 0.6-0.8V, see if you can drop the terminal voltage to 70Vdc or so.

A good hi-res image of the board would be next.

1n5404's for favourite

Attachment 28513
Here you go

I happened to be looking at the manual for the EM806 a couple of days ago. I think it said the the max voltage rating was indeed 80V (hence the name, from 80V and 6A) but although the internal mosfets were nominally rated higher than this, the recommendation was to keep the supply rail to 10% lower to allow for back emf, spikes on the supply, etc. Hence recommended 72V.

Thanks for the image - tbh I'm not comfortable in using that to try to diagnose further; I've just reviewed my images of a strip down of a 2DM860H repaired (details on this forum) and I've a DM860T stripped down in front of me. Both have SMDs on front and rear of board - the 2DM having lovely silk-screen printed ADC monitor points, the 860T is rather closer to the EM806 board in being rather non-descript.

If you look at the board it's a fairly conventional, common design. The HV stuff is on the left, largely isolated from the LV stuff on the right (the break point being around the 8-pin devices U9/U10/U11/(U12?) - centre of board. What you're looking for is a signal line that provides a HV feed from the left to the right and then into a resistor cluster. The problem is the resistor cluster may be on the rear of the board (it looks to be on the 2DM...)

Something like

Attachment 28514

but again - pure speculation. The image isn't sufficiently detailed to sensibly diagnose from a distance, and I do think there's stuff on the rear of the board that can come into play here. I was hoping to find a couple of resistors that looked shifty enough to probe to find your 73V, your 0V, and somewhere as a ratio (based on resistor values) between this as a feed into the ADC.

I'd say try to drop your terminal voltage, but as Neale said - the device should work to 80V (I've read more of the manual and I concur with his statement - though the manual also injects a useless 68V to confuse even more). But, beyond that and a truly high res image of both sides of the board I think trying to diagnose remotely isn't going to be very forthcoming. Previous experience is you'll need to be flipping the board frequently to trace potential signals through board vias... and I'm guessing the forum is processing the images - there's a lot of compression noise when you blow them up.