Troubleshooting internal ground fault on Fire-Lite MS-9050UD

Howdy y’all.

I’ve just now gotten to powering up my MS-9050UD that I was given, and it seemed to have been installed in a church, as evidenced by some of the device names (“PARISH HALL PULL STATION”, etc). Luckily, the codes were still completely default and I was able to clear the device programming. However, there still persists a ground fault, and it must be internal because I had no devices installed when I hooked it up. Does anyone know how I might go about troubleshooting it, or if that’s even possible?



Video will be forthcoming.



Thanks!

[YouTube]9POuP6S4bRA[/YouTube]

Here’s the video. Not entirely sure how to tackle this here.

Take a good look around the screws that hold the circuit board to the metal chassis. Some or possibly all of them will have a circuit board trace going to the screw hole. There may be some on the bottom side of the board. Those traces are the ground connection for the internal suppression devices. Those usually are across each circuit and from one side or both sides of circuits to ground. There are usually Metal Oxide Varistors, identified on the board as RV#. Some manufacturers use Transorbs that are a special kind of diode, which usually are identified as D#. The suppression devices will be around the SLC, NACs, other communication circuits, and low voltage power terminals for external devices. There can also be suppression devices in the power supply area of the board.



Remove the mounting screws one at a time, isolate the underside of the board from the mounting post with apiece of paper. Then power up to see if the ground cleared. Keep trying this with the various mounting screws to find the section that has the ground. Keep in mind there could be more than one ground. If an isolated section clears the ground fault trouble, look around that area for a damaged suppression device. There can be some on the bottom of the board.



If you locate the section that clears the ground keep it isolated. It will not be a problem in a hobby system that has all the devices close to the panel.



Obviously, a system protecting life and property must be properly repaired by replacing the board or panel. Any wiring going outside the building should be twisted shielded pair with the shield grounded at the point where the wiring leaves the building. The inner conductors should connect through a commercial grade suppression unit installed per the manufacturers instructions.

I’ve inspected the board and found two screw holes that seem to have traces. If the issue lies with these, will isolating both of them clear the trouble, or will I have to find the exact spot?

I would try isolating both of those points to see if the ground is in that area. There is a circuit trace running between them so it takes isolating both. While I don’t think anything bad can happen trying it, if there are multiple bad suppressors some voltage could be passed from one circuit to another. I enlarged the photo but could not see any of the components with obvious damage. There may be more devices on the other side of the board.



The components labeled BZ# are suppression components. I did a search on the lettering on them (BFT91A) but came up empty. I do recognize the little symbol on them. I have seen it before on other suppression devices.

Imgur: The magic of the Internet



Just tried it; no dice. Still got the ground fault.

There are what appear to be solder pads on the other side of the board. I’d have to remove the board again to show you.







And upon even further inspection…



There are two additional traces on the other side of the board.

You might want to check the other mounting screws around the board. It is possible there are suppression components around the power supply section of the board. It is also possible the IC chip that is in the ground fault sensing circuit is damaged.



If you have a voltmeter check the voltage between chassis ground and a negative power terminal. The negative of AUX power or the negative battery terminal. Lets find out what that voltage is.



I expanded the pictures and went over them looking for any possible compromised components: cracked, bulging, little black spots by them, etc. I can’t find anything that looks bad. Obviously something is bad.

I powered it up on a piece of cardboard, on a completely non-conductive surface. Still a ground fault.

I’m thinking this panel is toast.

Update: I found out that JP1 (the jumper right above the LCD) disables ground fault supervision, so when I go back home in May I’ll try that to clear the ground fault.



My question now is, will operating the panel with a ground fault ultimately lead to killing the panel? Because I know some ground faults can be fatal.

A real ground fault on a circuit can and certainly will pose a threat to the reliable operation of a life safety system. It is less common, however, for a ground fault to cause internal component failure on a circuit board.



It seems like, in your case, the panel is indicating a false ground fault due to an internal ground fault detection error, maybe a bad IC or a bad circuit trace on the ground fault sensing circuit leaking to ground somewhere. Since this is an internal panel problem and not a true ground fault, you can almost certainly use the panel on a hobby system and you’ll most likely never have a problem, so feel free to cut the jumper.



If you wanted to be super sure, with the panel powered off and seated on a non-conductive surface (like the cardboard), take a multimeter and check for continuity between the ground reference point (whichever standoffs have the contact pads) and things like the +/- SLC and NAC connections, to be sure there’s no internal fault on the panel causing any of those to leak to ground.