All engine controls dead after shortcut: MDI box fried?

[Krumelur]

In another thread I describe how I replaced the heat exchanger on my D2-55, which went surprisingly well.
But in the end, Murphy got me.

When I tested the engine after the repair, I would get a battery warning in the display of the RPM gauge. I measured here and measured there but could not identify a problem.
There was no under voltage lower then 13V and not over voltage above 15V. The starter. battery was at 14.6V and the LiFePo4s at 14.3V.
I'm charging using two Victron B2B 30A chargers. The starter battery is new, so are the the LiFePo4s and also the generator is a brand new 115A Mitsubishi.

When searching more, I found that the +12V sensing cable connected to the generator was damaged, cracked and fell off the moment I touched it.
I gave it a new wire terminal and didn't pay attention while reconnecting it to the generator: I made contact with the generator's casing and the sparks were flying.
When all was done, I wanted to check if the battery warning had gone but then the engine controls were dead.

- Pressing the power button on the MDI control panel in the cockpit won't power up the display of the RPM gauge.
- Starting the engine is no longer possible, pressing the starter button does nothing.

I checked the following to see if it was any main fuse that would have been blown:

- There's +12V leading to the starter
- There are +12V leading to the MDI box

That makes think that, no, there's no fuse blown.

I opened the MDI box to see if it has a fuse in it. Negative. This is one of the old versions without a fuse.

I have now ordered a new MDI box, hoping that it will fix the problem.

Can anyone comment on the issue and confirm that what I did could actually blow the MDI box?
I have the old MDI box here, is there any way of verifying that's it's fried?

[sean c]

I am not an expert on MDIs but the following link will take you to someone who is.
https://nordkyndesign.com/engine-reliability-a-look-at-the-volvo-penta-mdi-black-box/

There is an MDI wiring diagram in the workshop manual in the Download section of the site.

https://bavariayacht.org/downloads/engine/Volvo%20Penta%20Electrical%20System%20D1%20D2%207748428.pdf

Might be time to consider a bypass system to so you are not vulnerable to the black box reliability.
My boat has the EVC panel inside next to the engine. At the helm I have two 'momentary' buttons. One connects power to the on/off wire in the MDI. See wiring diagram. The other one is a much thicker wire that connects the 'batt' terminal to the 'start' terminal on the MDI. I also have a cable and casing attached to the manual fuel shut off on the engine. Pull the handle out to stop the engine.
You don't actually need the MDI to start the engine. The fuel solenoid fails open and needs power on to shut it off.
Sean

[Krumelur]

Thanks for the link to the wiring diagram.
My concern is not so much I would start the engine in case the box is failing, but about fixing the current problem.
Is there a chance anything else is damaged besides the box?
I have already ordered a new box, but it will be a 6h trip to the boat and if the box is not the solution, I will have to drive back home and start thinking again, so I would like to consider all other options before leaving.

[Sootydog]

I had the exact same problem last season.

Removed the alternator for investigation and forgot to take a photo of the wiring thinking I had a good enough memory. 

I found a small pink(??)  wire had broken and after i fixed it and put it back where I thought it should go there were a few sparks and
The starter would only work sporadically.  No engine revs on the tacho.  No engine hours on the tacho .  Voltage warnings.  Just wouldn't stop using the control panel.

A local marine electrician diagnosed the black box was fried.

I started the order process for a new one at a VP specialist who said it might be better if they took a look first.

30 seconds after he arrived, he showed me the wires (plural) that i had in the wrong place and swapped them over. Hey presto, it all sprang into life.

Is there any way you can get a VP experienced person to look it over?  The box might not be fried.

[Krumelur]

In my case, I did not remove any wires. All was working and then was dead after the sparks.