I have a Propex HS2000 Propane heater for my van. It is broken. It has a rudimentary diagnostic system, that flashes a code for various errors. It is flashing 5 times, indicating a issue with combustion airflow. I did ensure that the airflow passages are clear.
I emailed the manufacturer an got no response, and I talked to the local distributor and they will happily swap parts, but they wont help diagnose and do not have a schematic.
I then dissasembled it and looked at the airflow sensor. It is a minature passive fan, with black/white optical encoder sensed by a photocell/ir emitter combination. This attaches to a small op-amp circuit to convert the sine wave to the square wave then goes into a PIC uProc.
I put a scope on the sensor output and it shows a 0.15V on the sensor for about 5 secs, then shuts of power to the sensor, shuts down the unit and flashes the diagnostic code.
So I took the board out of the unit, took a bunch of hi-res pics, put it back together, and it now all works. Just for fun I did another scope shot to measure both the input analog and output digital signal.
Nothing like a problem that cannot be reproduced at will. Assuming there is a cold joint or cracked resistor or poor connection, I broke out the trusty chopstick and poked around. I could not get it to fail.
Any tricks on how to find a non-reproducable, intermittent fault?
I emailed the manufacturer an got no response, and I talked to the local distributor and they will happily swap parts, but they wont help diagnose and do not have a schematic.
I then dissasembled it and looked at the airflow sensor. It is a minature passive fan, with black/white optical encoder sensed by a photocell/ir emitter combination. This attaches to a small op-amp circuit to convert the sine wave to the square wave then goes into a PIC uProc.
I put a scope on the sensor output and it shows a 0.15V on the sensor for about 5 secs, then shuts of power to the sensor, shuts down the unit and flashes the diagnostic code.
So I took the board out of the unit, took a bunch of hi-res pics, put it back together, and it now all works. Just for fun I did another scope shot to measure both the input analog and output digital signal.
Nothing like a problem that cannot be reproduced at will. Assuming there is a cold joint or cracked resistor or poor connection, I broke out the trusty chopstick and poked around. I could not get it to fail.
Any tricks on how to find a non-reproducable, intermittent fault?
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