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Marathon Techlink Display Temp AC DC and Control
This past summer I did a little project on the bus to correct the erroneous displays for black tank, grey tank, fresh tank, voltage readings to house and chassis, and temperatures displayed on Marathon Driver Screen and fix a bathroom light and fan switch that was bad. What I did is not for the DYI’r without some knowledge of how the system works. This is meant to give Marathon Techlink owners with a similar system the knowledge on how the display shows you the readings.
All the readings on the Marathon driver screen are generated by a series of sensors giving voltage inputs to the two computer boards called the Waterbay Board and Generator Bay board. The water bay and generator board convert the voltage 1-5 volt inputs from the sensors and sends the output to a video box in the overhead above driver (my bus not yours) that converts signal to VGA and allows monitor to display it.
To do this work I contacted Brain Gabel of EDSI who design and manufactured the Techlink System for Marathon. A laptop was sent to me and over the phone and internet we refreshed and reprogrammed the two main computers on the bus. So…….do not attempt this if your skills in computers and mechanical are subpar.
During the process of doing this reprogramming we discover bad bay computer boards, sensors, and switches. So we would have to stop I would do some leg work and then we would get back on the phone and keep going.
The Sensors:
1. Tank – The grey, fresh, and black tanks on my bus (not yours) uses a MXP5010DP Motorola/FreeScale pressure transducer that senses the return air pressure of air being blown into a tube that by tracing the fish pump air tubes goes into top of tanks and the tank tube goes all the way to bottom of tank. With the three fish tank air pumps supplying air the pressure into the tube in the tanks … there is a 10 second timer on the system (why your pumps run and then stop) and pneumatic check valves are locte in the pump line to keep air from bleeding back into pumps and routing it to MPX5010DP sensors in the system.
When the pumps stop it allows the MPX5010 to measure the head pressure in tube (there one sensor for each tank) MPX5010DP (Newer Model then what was install originally). Your system has to be air leak free for this system to function properly and your pumps should be changed out every few years (because they are not commercial equipment). Marathon eventually replaced this system with glued on pads but the new system uses the same 1-5 volt inputs to waterbay computer board. The system is flicker but works. It is the input into water bay board that are critical.
2. The temperatures in the bays, cabin, and outside temps displayed on the driver screen occur by the system getting reading from the temp transducer AD590JF-ND temperature transducer signals to the water bay board. The board has to be programmed using coded steps that only Marathon or EDSI knows how to do.
3. The generator board controls all things AC and DC on the bus. If you press the generator start/stop button from your driver dash it goes through this board.
The generator board and the water bay board are the same computer board just programmed differently.
To do this you need to know that when the tanks are empty or full and record the readings. What the temperatures are outside inside and record the readings. What the voltages are AC or DC and record the readings. There is a lot of back and forth looking at the display in bus and going back outside to the bay where the waterbay and generator bay boards are located.
Your AC and DC system must be functioning correctly. You can get your DC readings at the Klixon breakers in the battery bay for house, chassis at engine, and generator at generator. Check your Vanner readings as well for house and chassis.
When you press your SMX pad to control your Air Conditioning and Heat in cabin there is a temp transducer located inside the housing (black ribbed) in the picture below. This same transducer is located outside on the front bumper (4 each on my XLV) and in the bays. Marathon scatters a temp transducer in a black ribbed device in all of the zones you have air conditioning/heat. They are under the cabinets in galley and bedroom and over the drivers head for salon (my bus not yours). I took the salon unit apart because when trouble shooting we were not getting a signal to the water bay board. After testing it was a bad temp transducer. In the picture it is the .25 diameter aluminum cylinder looking thing 1 inch long hanging down. Next to it is a AD590 wired in. You can buy the finished part from Marathon or Dometic (Crusair) but what is the fun in that. I bought the AD590 from Digikey …the AD590 is what is potted inside aluminum tube with conductive epoxy.
The reason there are two of these sensors potted into the black ribbed housing; 1. is the temp sensor for your SMX HVAC system control and the other is the signal to dash display through water bay board. When you replace the temp sensor you should not have to reprogram your waterbay board. But what we discover is the Marathon had reprogram med the board previously and did a bad job. So using a laser temp reader I went around the bus and reads the readings at the balck ribbed housing and Brian Gabel repgprogram the water bay board so the display at dash read properly.
This is a general overview of how this Techlon Technlink sensor system works.
I already had parts in hand to fix anything bad.
In the end three days later working 4 hours per day the readings on the driver display are more accurate and I know way more about how things operate. It was an education drinking from the fire hose in 90 degree plus days.
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5 Replies
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Ed: I’m awfully impressed!
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Well done Ed, very informative for Marathon owners.
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Ed,
well done! Thanks for shedding some light on the internal Techlink workings. My three fish tank air pumps are getting noisy after 21 years. Still provide accurate tank levels but probably should replace them before our next major trip or at least carry spares.
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Here are some more reference pictures. The Water bay board and Generator Bay Boards are located in Overhead J-Box 2nd Driver Side bay my Coach. Timer For Air Pumps is located inside a standard electrical box in water bay where pumps are at. The MPX Transducer is a automotive product located on a small printed circuit board in the water bay above the timer ..just trace your fish tank air lines to it.
The air pumps were replaced because the existing ones were eighteen years old. The previous pumps were original and very good quality and could be rebuilt, but, the company went out of business. I bought the ones in the picture to match up against the air pressure the existing pumps put out to not effect any programming efforts. The air pressure to the MPX5010DP Pressure Transducer when timer is off is critical for system to function properly.
I also replace all fish tank airlines with silicone fish tank airlines per Brian Gabel suggestion. Think about that one for a minute when buying 1/4 fish tank airline.
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Hey, Ed, I was wondering if your tank monitoring is still holding up. I replaced my pumps but must have used too cheap/weak pumps I think. Plus, I didn’t get it air tight as the levels drop right away.
It looks like you used the Coralife blue pumps currently at ~$50 each. Those are adjustable. Did you set yours to the max L/min setting? I also used ‘normal’ tubing, not silicon and maybe I’m getting a poor seal. It needs to be 1/4″ OD, right? Where did you get yours?
I’ve thought about converting to stick-on sensors, but access to the side of the tanks is not great and overall seems sketchy.
Thanks.
Terry
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