Hello good people of this forum,
My name is Kyle, and I'm at my whits end, I wont bore you with what I've tried and haven't, or my story of any kind. All you need to know is Propex believe my main PCB to be at fault, I've tried the reset, no joy it actually doesnt start its usual cycles as you would expect. I cant afford a new board, I've been scammed by buying it and I could use a hand. I'm ok with a multimeter I can only begin to imagine the intelect needed to fix something like this, so please be patient with me. It's a 12v system, If we can't get this working I may ask for some help with simply building a new one.
I've included the photos of the PCB GHC252 which is my least favourite thing on earth at the moment.
Thanks in advance to you guys
Kyle

P.S
I'll try and get a better photo than this,
TAB 1 is the ground point for the HT lead
CON1 is 12v
CON 2 is the thermostat which holds the error light
CON 4 is the power for the fan
CON 7 is gas valve
CON 8 is an air sensor that senses the air passing over it by sucking air over a fin that spins, it then recognises the data via white and black markings

 

Looking at the picture this looks like a forced air gas (maybe propane) fired little furnace as used in some RVs and campers. These things generally use a sort of permissive loop for safety before ignition happens. Normally a thermostat or sorts or switch calls for heat. The heater motor or a combustion blower should start. The system should go through a purge for maybe 10 to 20 seconds and during this time a switch or sensor senses the airflow making sure the plenum is not blocked or obstructed. If things are good then a gas solenoid valve turns on and an igniter fires the gas for combustion. At this point some use a flame detector to make sure there is flame but not all work this way. The heater should be running and heating until the thermostat set point is reached. Some units also have an over temp shutdown which is generally a normally closed switch. If that switch is open the unit won't run and go through its start cycle.

Have you checked the air flow sensor you mentioned? That should be normally open and close with air flow. Unless it senses air flow the system will not turn on gas or start the igniter. The thermostat you mentioned should call for heat and start the blower.With 12 VDC applied are there any fuses and the 12 VDC is present I assume. Many times the failure item is not the main circuit board but an external sensor or switch.

Less an actual schematic all I can give is pure speculation on my part based on hos similar systems I have seen run. They will not fire the gas until a series of safety switches and conditions are met and they won't maintain an open gas flow unless they sense a flame.

Ron

 

Ron my friend you're absolutely right in everything you've just said . How would I test the air sensor? I mean I can see it's moving! If you Google propex hs2000 air flow sensor you'll be able to see what it looks like. Can I check to see I'm getting a reading. It goes straight into gas lockout, doesn't try to fire and yep it has an external thermostat switch sensor thing. Shall I put a picture of that up to? Its actually a simple board, i could work it out (you'll see and laugh at me!) I'm inclined to believe it's not this main board, I've just got a gut feeling.
Kyle

 

Here's the sensor that's giving me the questions

Top

Bottom

 

A Google of the part number brought up all sorts of stuff. Then I tried "Testing propex hs2000 air flow sensor" and a few things came up you may want to try. Good pictures but I am not sure how they are sensing airflow. I liked the old fashion lever switches with a small paddle in the airflow. These heaters are apparently real popular, as I said, Google went nuts. Problem is I don't know how to do a workaround just to test the thing (sensor). You might give it a shot with the phrase I used including the word testing.

Ron

 

I've bought a new sensor, they work similar to a maf sensor with no moving parts, I'll post back when I've received it and recovered from the arm and leg they removed to pay for it.
Thanks again
Kyle

 

Kyle,
Yeah, I can't believe the cost on that stuff. Sell a kidney and buy a new control board for my furnace. Years ago you bought a new thermocouple for five bucks and fixed the furnace. Let us know how it goes.

Ron

 

It looks to me like a reflective opto sensor. In the background of the side of the board with the resistors there is what looks like an impellor with radial black and white stripes on it. I think it should generate a string of pulses when the impellor rotates. I suspect the orange wire is DC+ I think the green is the common (DC -) and I think the white is the output pulse. (The text behind the wires is obscured by the wires.) If you connect your multimeter (Set to the 20 volt DC range.) between the green and white wires you should see a level change if you hold a piece of white paper in front of the reflective opto sensor. If you mount the sensor board back in position and turn the impellor very slowly you should see the voltage level change on the white wire as the black and white stripes move in front of the sensor. I don't know how safe it will be to do this test as I don't know how close you will be to any high voltage connections.

Les.

 

Can you make out any numbers or letters on that blackish IC. They may only be a few characters and make no sense.

==

Something called "flame rectification" is used in some system to detect a flame. A rod is placed in the flame with an AC voltage across it and ground. The detection circuitry must have the correct phase with respect to ground and that sensor MUST be clean. It can be cleaned with sandpaper.

IR flame detection is another.

You MAY have a pilot that ignites first. Spark ignitors and hot surface ignitors are both used.

 

Can you make out any numbers or letters on that blackish IC. They may only be a few characters and make no sense.

==

Something called "flame rectification" is used in some system to detect a flame. A rod is placed in the flame with an AC voltage across it and ground. The detection circuitry must have the correct phase with respect to ground and that sensor MUST be clean. It can be cleaned with sandpaper.

IR flame detection is another.

You MAY have a pilot that ignites first. Spark ignitors and hot surface ignitors are both used.

Ohhh sounds promising, what's an IC? Where have you seen it in the photo?
Regards
Kyle

 

Ohhh sounds promising, what's an IC? Where have you seen it in the photo?
Regards
Kyle

See below...

 

Ok I'll get them in the morning for you @GopherT what are you hoping to find from that?

 

Kyle, I know you have likely tried this but looks like a thermal switch on the side plate with the red button. Would that be a pop type reset? Does the button press in and click? Those are generally normally closed and open on a temp rise so if you measure the resistance across it you should see less than one ohm.

Ron

 

@Reloadron yes I've pushed that in, and bypassed it. But it won't hurt to try! I'll do this anyway! In the meantime can someone make these things...... Only cheaper??!!?!?

 

@Reloadron yes I've pushed that in, and bypassed it. But it won't hurt to try! I'll do this anyway! In the meantime can someone make these things...... Only cheaper??!!?!?

They should not cost what they do. I see furnace boards all the time which at most should be a $50 part and they cost $350. It's a racket. Every year as we start winter I say a prayer to the Furnace Gods and ask for another trouble free winter. My sister's furnace uses a filament igniter, a simple filament in a base plug. They cost $50? Not sure what is in mine and hope I don't find out in January.

Ron

 

Interested in any numbers or letters on the pic you posted in post #4 on that thing with six legs on it.

 

Well I replaced the sensor this morning.no joy . I could cry it's such an expensive thing. I'm going to have to replace the pcb. I've included the photos of the ice that I can get to. If you think of anything let me know. I'm off to go and cry about the times I had money

 

Have one of you guys got the knowledge to build one of these circuit boards? These things are so expensive. I'm trying to work out why!

 

Have one of you guys got the knowledge to build one of these circuit boards? These things are so expensive. I'm trying to work out why!

Can I ask you have you started this thread due to getting the 5 flashes on the stat?
If so I am in the exact same situation. I cannot believe Propex can sell such an expensive upgrade for a piss poor original set up & not back it up when its not working. Has any body got an opinion on bridging / blanking this sensor out of the system considering that the air flow is clearly there but not recognised.

 

Have one of you guys got the knowledge to build one of these circuit boards? These things are so expensive. I'm trying to work out why!

HCF4541BE is a programmable timer,

https://www.google.com/url?sa=t&sou...Vaw1MTP2iqDkE7EjGEj1OWWuO&cshid=1538144322346

MCP601 is an op amp from microchip.

https://www.microchip.com/wwwproducts/en/MCP601