A furnace PCB test JIG.

[capwizard]

A furnace PCB test JIG is under construction!

First I need 24vAC transformer, found't on useless clone solder iron station.

Use hair dryer as blower motor.
PS: Will test why blower motor is running erratically....... After this I will read the microcontroller program then Zip files for Badcaps veterans..........stay tuned.........


PS: Now, TRUMP INAUGURATION 2017, Woo, my guess was wrong she is wearing a sky blue coat.

https://www.nytimes.com/video/us/pol...uguration.html

[budm]

Re: A furnace PCB test JIG.

Aren't the relay contacts isolated from each relays and from the circuit?
If they are then you use one wire of the 24VAC winding to feed the relay contact, the relay contact out can feed DIODE-RESISTOR-LED, then the other leg of the LED will go to another lead of the 24VAC wire.
The blower motor gets the power through the relay, right?

[capwizard]

Re: A furnace PCB test JIG.

"The blower motor gets the power through the relay, right?" YES.
I need to bypass all the sensors, then test whats cause erratically problem.

I need help on FS, frame sensor output voltage or resistance, how come, it is floating?

Reference:

A flame sensor "senses" a weak DC signal from the AC power sent to the ignitor which via the phenomenon of flame rectification in which the polarity of power sent through a flame is rectified to DC, flame is a poor conductor so the signal is mere micro amps .3 to .5 usually and the flame sensor is nothing more than a rod insulated y a ceramic base so it is not in contact with anything , the flame sensor is a rod that's all and wired to the sensor termination the control board. if the unit has no flame sensor it uses the burner ground or burner assembly to transmit this signal, this is why cleaning the sensor with steel wool will often fix a flame sensing fault.

Generally its either by thermocouple or flame rectification. Tc is where a probe is heated and a small microvoltage differential appears between the outher and inner core usually holding a magnet to keep the pilot valve open. Flame rectification is where a small dc voltage is taken from the flame monitoring board passed through the flame to a rectificatiin probe which returns the voltage to the baord keeping the gas valve open. Theres a bit more to it but tbat will suffice for
If you are talking of a pilot light (flame sensor) in a natural gas or propane, residential furnace, the valve has a micro-voltage probe (thermocouple) that generates a small electrical current when heated (by the pilot flame.)

Temperature Sensing Devices and Optimization of Temperature Acquisition Systems
Attach files: PDF

GMP075-4
https://cdn.badcaps-static.com/pdfs/...e2ee1acf8b.pdf

[budm]

Re: A furnace PCB test JIG.

The Flame sensor: the circuit is completed through the FLAME. Source impedance is high so the detection circuit requires high input Impedance (Z) and that is why JFET is used..

[capwizard]

Re: A furnace PCB test JIG.

Maybe I can use solder iron tips as A Flame sensor, at least as for a HSI (Hot Surface Igniter)? Arrr.....I don't need the flame sensor, but I need a voltage or ground it let PCB think there is no flame there, because problem occurs before furnace lights up.

[capwizard]

Re: A furnace PCB test JIG.

Troubleshoot the circuit board of the gas furnace
https://www.youtube.com/watch?v=LxOUHEZiIx0


PS: Isn't she gorgeous!.............. Diana, Princess of Wales alive? No, princess Diana has bigger eyes than hers.

[capwizard]

Re: A furnace PCB test JIG.

Now the test JIG is blink twice a second, I connected GV (gas valve) and FS (flame sensor) to Chassis Ground still have problems, test JIG is at (not ready mode), I need help!

PS: Will using wire connectors. PLs dont bug me! Pressure sensor is normal open. Don't understand AC has Chassis Ground?

PS: GV (gas valve) uses a 320 ohm resistor to Chassis Ground still the same.

PS: rapid continuous error code shows is Reverse Transformer Secondary leads, reverse primary wires? Is AC 24v have ground? How can I test it? by the coil wiring direction? How the PCB knows that?

Reference:

Gas furnace integrated furnace control #2
https://www.youtube.com/watch?v=4_l6hc2bKFI

The simple check of the gas valve
https://www.youtube.com/watch?v=0zKl9wvNIRk

Furnace Gas Valve Test | Rochester Heating & Air | Furnace Repair Louisville Kentucky
https://www.youtube.com/watch?v=YlFBlwKWndE&t=2s

How to test the gas valve on a gas furnace with an ohmmeter
https://www.youtube.com/watch?v=hHmT-VfV-bY

[capwizard]

Re: A furnace PCB test JIG.

I probably need to change to metal case for Grounding?

[sam_sam_sam]

Re: A furnace PCB test JIG.

You need to be careful when bypassing control devices on controllers
If you bypass it the wrong way you may burn up the controller at worst or fry the I/O inputs

Or you will not get the controller to work right

[redwire]

Re: A furnace PCB test JIG.

Use this circuit to simulate flame detect. Shorting the flame rod to GND is an error condition, not flame. Flame has a rectification property the controller checks for, as a short-circuit/leakage current/soot etc. is not a flame.
Also, the controller will not want to see flame detected before the gas solenoid is turned on and igniter activated.

When I see the igniter output ON, then I flick the switch to (simulate) flame present. You could activate a relay with the igniter output+gas solenoid.

If the igniter is a HV sparker (not hot-surface) then the diode gets killed from the high voltage when sparking to light the gas. You can use a 1kV array (5 of 200V) TVS or a gas-tube across the flame rod. That way, ignition voltage just arcs across the gas-tube or hits the TVS, and the diode is protected-you can still flip the switch to fool it into "flame present".

PS the 24VAC XFMER does have a ground connection on one leg (BLK)

[keeney123]

Re: A furnace PCB test JIG.

"The blower motor gets the power through the relay, right?" YES.
I need to bypass all the sensors, then test whats cause erratically problem.

I need help on FS, frame sensor output voltage or resistance, how come, it is floating?

Reference:

A flame sensor "senses" a weak DC signal from the AC power sent to the ignitor which via the phenomenon of flame rectification in which the polarity of power sent through a flame is rectified to DC, flame is a poor conductor so the signal is mere micro amps .3 to .5 usually and the flame sensor is nothing more than a rod insulated y a ceramic base so it is not in contact with anything , the flame sensor is a rod that's all and wired to the sensor termination the control board. if the unit has no flame sensor it uses the burner ground or burner assembly to transmit this signal, this is why cleaning the sensor with steel wool will often fix a flame sensing fault.

Generally its either by thermocouple or flame rectification. Tc is where a probe is heated and a small microvoltage differential appears between the outher and inner core usually holding a magnet to keep the pilot valve open. Flame rectification is where a small dc voltage is taken from the flame monitoring board passed through the flame to a rectificatiin probe which returns the voltage to the baord keeping the gas valve open. Theres a bit more to it but tbat will suffice for
If you are talking of a pilot light (flame sensor) in a natural gas or propane, residential furnace, the valve has a micro-voltage probe (thermocouple) that generates a small electrical current when heated (by the pilot flame.)

Temperature Sensing Devices and Optimization of Temperature Acquisition Systems
Attach files: PDF

GMP075-4
https://cdn.badcaps-static.com/pdfs/...e2ee1acf8b.pdf

The flame sensor generates its own voltage. The heat from the flame creates this voltage because of dissimilar metals in the thermocouple. It does not need any outside source or ground to do this. Kind of like a battery. This is why it is floating. The micro volts that are generated keep the gas value open. When you first light the pilot light you push in on the gas valve. This then brings the end of the valve close to were the thermocouple connects to. I believe the micro volts create enough magnetic effect to keep the valve open. The end of the valve is isolated from the gas going through it. When there is no micro volts generated by the heat of the flame the magnetic effect is gone and the valve closes. Honeywell is one maker of these micro voltage relays and you can read about them on their site in case I have not remembered everything.

[redwire]

Re: A furnace PCB test JIG.

I think the heating industry is no longer using thermocouples as flame sensors (for anything but pilot lights) because they are too slow and not reliable.
If a main burner flame out occurs, it takes many seconds for the TC to cool off- meanwhile the gas solenoid is on. This flame-failure response time has to be under 4 seconds according to NFPA.

Thermocouples generate tiny ~20millivolts but make high current (100's mA) that can pull in a relay. I just don't see them used anymore in modern furnaces.