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Old 07-24-2012, 04:15 PM   #1
Site Team - Lou
Herk7769's Avatar
Join Date: Oct 2009
Location: South Eastern PA
Posts: 23,102
Troubleshooting the MicroMonitor FAQ

Well, after I installed the Horst Miracle probes I thought I was done with this issue, but while my black tank works perfectly (still) my gray tank is reading full all the time. Since I was assured my Horst probes were impossible to fail due to gunk in the tank I assumed I had a MicroMonitor problem.

Used the MicroMonitor trouble shooting guide (attached) and hit a wall. So I called Terry at KIB Enterprises (KIB Enterprises - Excellence in Electronics) and we went through all the steps to eliminate the MicroMonitor and its components one more time.

What was really interesting was the way the system lights the lights. I thought that the top probe would turn on the full light (all of them) and the 2/3 probe would light 3, etc. I knew the empty light is the "power available" indicator and not really in indication of what is going on in the tank.

So, for the techies out there:

The red wire from the control panel passes 8 volts DC when the tank selector is pressed to the resistor pack (a red plastic lump with 4 wires coming out of it called a K101 pigtail). If there is no current path to ground the OPAMPS in the monitor circuit board do not fire to turn on the 1/3, 2/3, FULL LEDs.

If the lowest probe (all things working perfectly - Yellow wire) has a path to ground the 8 volts is dropped across a 188K resistor dropping the line voltage from 8 to 6 volts. This drop fires one opamp turning on the 1/3 LED. As the water rises and the 2nd probe is covered, an additional 68K is added to the circuit dropping the line voltage to around 4 volts. This fires another opamp turning on the 2/3 LED. The full probe is a direct connection to ground and the voltage drops to 2 volts or less, lighting all the LEDs.

What is interesting is that if the 1/3 (or the 2/3 for that matter) probe gets contaminated with crud (gray tank soap, or grease), for instance the conductance of the crud on the probe and wall to the ground probe is added to the circuit reducing the voltage as if the probes above it were covered when they are fine.


Not that it matters, but you can actually determine which probe is actually "bad" by removing all the wires from the three probes on the right and connecting them one at a time to the ground probe. The lights should come one properly is the system is working as advertised.

The solution, since it is the probes in my case, now involves finding out if I can clean them without damaging my Horst Mircale probes. I have contacted (but not gotten an answer yet) the maker of the Horst probes to see if a Gallon of "Simple Green" dumped into the gray tank (and then fill it with water) will dissolve the crud without dissolving the probes.

If they do not get back to me, I am just going to give it a shot before I order a new set. (Film at Eleven...)
Lou, Laura, & Freya the wonder dog
2008 GMC Sierra 3000HD Crewcab SB Allison Duramax
2019 Flagstaff 8529FLS - Pullrite 3300
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