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Old 07-13-2021, 05:20 PM   #1
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Precision plex system electrical issues

Hey guys, I currently have a 2019 Dynamax dx3 37bh which I have been keeping in storage down in Florida. I recently drove it back to IL, where I have had it sitting in my driveway. A couple days ago, I fully disconnected power to the rig, as I needed to replace the chassis batteries. After doing so, everything seemed to work fine, but then all of a sudden the Plex system died. Completely.
Light switches don't work, the green lcd on the master panel is blank, and the touch screen is dead. I checked the inverter, which works fine, replaced the 350amp main fuses in the battery bay, and checked inline fuses according to dynamax's direction. At this point I have no idea what to do, so any help would be greatly appreciated!

-Dave
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Old 07-13-2021, 05:48 PM   #2
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Are you plugged in and verified that your batteries are being charged?

The plex system is voltage sensitive in that it requires your batteries to be at a certain level before it will activate.
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Old 07-13-2021, 06:16 PM   #3
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Yeah, they show up as being charged. I am currently connected to 15 amp shore power.
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Old 07-13-2021, 07:44 PM   #4
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I would fire up the generator and run it until the batteries go to Float Charging mode. At this point, you can be sure batteries are sufficiently charged and begin troubleshooting.

Several years back we were helping someone that was plugged into 15 amps shore with all kinds of squirrelly symptoms. I was learning about my rig then too so I dug into the battery charging circuitry. If I recall correctly, I convinced myself that the only way a 15amp shore would work is if the charge state was at the Float Charging level.

Of course, with 15 amp shore very little could be turned on in rig and it is just in an “storage” state.
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Old 07-13-2021, 08:18 PM   #5
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Click the battery boost button on dash
It resets it to know that batteries are there again after they get drained completely
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Old 07-13-2021, 09:30 PM   #6
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I would fire up the generator and run it until the batteries go to Float Charging mode. At this point, you can be sure batteries are sufficiently charged and begin troubleshooting.

Several years back we were helping someone that was plugged into 15 amps shore with all kinds of squirrelly symptoms. I was learning about my rig then too so I dug into the battery charging circuitry. If I recall correctly, I convinced myself that the only way a 15amp shore would work is if the charge state was at the Float Charging level.

Of course, with 15 amp shore very little could be turned on in rig and it is just in an “storage” state.
Ah, ok. Would the 15 amp shore not charge the batteries sufficiently?
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Old 07-13-2021, 09:35 PM   #7
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Ah, ok. Would the 15 amp shore not charge the batteries sufficiently?
Depends on what else is on. residential fridge on inverter? Then likely not.
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Old 07-13-2021, 10:44 PM   #8
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Ah, ok. Would the 15 amp shore not charge the batteries sufficiently?
The battery charger goes thru several cycles to get to full charge. Starts out with Bulk Charging, then Absorption Charging, then Float Charging. During each of these cycles the voltage and current changes in various ways to get the battery to the most healthy state (See Magnum operators manual for details). But, the final stage (Floating) is like a “trickle charge” just to keep things topped off if you will.

If you start your generator, note the charging state on the inside Magnum display. If you have been unplugged for a period of time or have had your inverter on, you will likely start out in Bulk or Absorption Charging Modes. (You may have to cycle the charger button Off/On to get it to display). It may take a few hours to get to Float. Once there, then you can plug into the 15 amp shore and trickle charge. At this point, you can troubleshoot the PrecisionPlex without worrying about the impact the batteries may be having.

FYI. After hitting the Float Charge stage, I have had my rig plugged into 15 amps for weeks on end. Refrig was on, lights (LED), ran ceiling vents. Keep in mind, that the Charger is on ALL the time and it draws some power—but it draws the minimum at Float stage. As long as you stay under 15 amps total it should maintain.
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Old 07-14-2021, 07:07 AM   #9
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Depends on what else is on. residential fridge on inverter? Then likely not.
Batteries are in float charging, but the plex system still will not load up. Is there a sequence to re-booting the system that I need to be aware of? Such as Batteries first-shore second, or the other way around?
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Old 07-14-2021, 07:25 AM   #10
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Batteries are in float charging, but the plex system still will not load up. Is there a sequence to re-booting the system that I need to be aware of? Such as Batteries first-shore second, or the other way around?
When you say "won't boot up"...do you mean the touch screen? Or the brown panel that has all the fuses in it???

The touch screen is not the multiplex....it is just an interface like a switch. The brain is the bran panel with all the fuses and the small LCD screen. Everything is still controllable from there, or potentially the app. IF it is just the touch screen that is not booting up, I would pull that screen, unplug the data cable and plug it back in.
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Old 07-14-2021, 07:53 AM   #11
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Unfortunately I mean the entire system. Master panel as well is inoperable.
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Old 07-14-2021, 08:22 AM   #12
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I would go back and check that the battery disconnect is in correct position. If so, then check for voltage on both sides of it.

Reason: when you do a PrecisionPlex reboot, you remove power with the battery disconnect switch but it can take 10 minutes or so before the PrecisionPlex to actually power down. (This delay is probably due to internal capacitors that need to bleed down…just info).

If that is good, then check all the fuses in the electrical bay. Not sure of the fuse mapping, but there are only a few fuses and it is quicker to just run down them all with a multimeter to make sure you are not missing something.

When you said everything work fine for a while after battery replacement, how long of a period of time was that?
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Old 07-14-2021, 11:45 AM   #13
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I would go back and check that the battery disconnect is in correct position. If so, then check for voltage on both sides of it.

Reason: when you do a PrecisionPlex reboot, you remove power with the battery disconnect switch but it can take 10 minutes or so before the PrecisionPlex to actually power down. (This delay is probably due to internal capacitors that need to bleed down…just info).

If that is good, then check all the fuses in the electrical bay. Not sure of the fuse mapping, but there are only a few fuses and it is quicker to just run down them all with a multimeter to make sure you are not missing something.

When you said everything work fine for a while after battery replacement, how long of a period of time was that?

Fuses in the electrical bay are fine. I tried running the genny to get the batteries to float charging mode, but unfortunately the plex system still did not switch back on. I also tried starting the engine with the boost button, also with no effect on the plex system. Are there any fuses under the bed near the plex system I should be aware of? Precision circuits has been unresponsive for the past couple days.

Strange thing is,
The inverter is reading the batteries as fine, and every single appliance in the rig is operating normally. Hopefully it is not a board issue.
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Old 07-14-2021, 12:36 PM   #14
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Have you reached out to Precision Circuits?
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Old 07-14-2021, 01:53 PM   #15
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Have you reached out to Precision Circuits?
Yeah, just now. I tested the board power input with a multimeter, and found that the mains line in is not receiving power. I am wondering if a mouse chewed through the mains cable while it was in storage.
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Old 07-14-2021, 04:58 PM   #16
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Likely not the mouse since you said it was working before battery replacement. Stay focused on actions taken for that event.

Since lacking input power, you are going to need info about where the PrecisionPlex gets power from….need a schematic from Dynamax for that year/model. Otherwise you are going to have to visible trace cables….not fun but …
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Old 07-14-2021, 06:37 PM   #17
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I learned from RV electricity about a tool called a fox and hound. You connect the signal generator to the known end of a wire and can trace it through walls with the amplifier. Works a treat for following house and RV wiring through places you don't want or cant to open up!

Below is the one I bought. Click image for larger version

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Old 07-14-2021, 06:39 PM   #18
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With this tool, you can connect to the known end at the precision plex and follow it back through then"house" to the point where the signal stops. You'll know then where the interruption in the continuity is happening.

Good hunting!
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Old 07-14-2021, 07:19 PM   #19
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With this tool, you can connect to the known end at the precision plex and follow it back through then"house" to the point where the signal stops. You'll know then where the interruption in the continuity is happening.

Good hunting!
Now, I like that!! I have to have one…
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Old 07-15-2021, 08:07 AM   #20
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Interesting development,
I traced the mains wire from the precision board down to the trombetta solenoid near the inverter, and found that it is getting no power. Tracing the power to the solenoid from the battery bay, It turns out I have no DC power whatsoever from the batteries. AC power is working fine though.
Any ideas?

(The batteries are fine) (And yes AC is working off the inverter and not just shore)
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