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BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22387
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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where can i obtain a troubleshooting manual for a robert shaw

Customer Question

where can i obtain a troubleshooting manual for a robert shaw 780-715-U ? I have one that fires my propane torches and the pilot light won't come on. I need to trouble shoot to see if it's the controller or the valves. Greg
Submitted: 6 years ago.
Category: HVAC
Expert:  BillyHvac replied 6 years ago.
Chat Conversation Started
Billy :

hello, the control itself is pretty basic...do you get 24 volts to TH?

Customer:

yes I've got 24 v to the torch. The high voltage sparker works fine and I'm getting a good spark but the pilot light won't ligth. I vacuumed out the pilot propane supply tube and it wasn't dirty. I'm trying to figure if the pilot valve isn't opening or if the controller is not telling (asking?) the PV to open . Greg

Billy :

At the same time TH gets 24v the spark engages and PV sends out 24v. If spark is taking place...and no 24v from PV (pilot valve) terminal..control is bad. If there is 24 from PV then make sure 24v is going to pilot terminal on gas valve. If valve is getting 24v to pilot terminal, remove pilot tubing from side of valve and see if valve is sending pilot gas.

Customer:

is the terminal marked MV/PV simply the electrical common? I understand what you're saying however to put a voltmeter on it I need to be clear on the common.

Customer:

Can I send you a picture of the device? If so how do I do that ? greg

Billy :

I know the device well.....you are correct...mv/pv is the common for the pilot and main valve. You can use mv/pv if you like and the other meter lead to PV....pv energizes...sends pilot gas and spark at same time...IF pilot lights the sensor receives ok via sense rod...only then will the control energize MV>

Customer:

what is the "TR" terminal for? How does the controller receive the "flame OK" microamp signal from the torch head?

Billy :

Tr is what sends MV/PV back to transformer common. 24v olts leaves transformer, and goes through whatever control you have...a switch, a thermostat, safety etc. Then it comes out whatever activates it and goes to TH. Once at TH the control springs to life. The sensor rod is what verifies the flame is present. Some spark rods do it back to the control without a separate sensor..in this case the spark rod doubles as sense rod.

Customer:

So TR is really the other end of the common that completes the circuit after the relays?

Billy :

yes

Customer:

how does the spark rod signal get back to the controller?

Customer:

can anyone send me a trouble shooting manual for the robert shaw 780-715-U ?

Expert:  BillyHvac replied 6 years ago.
Chat Conversation Ended

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Expert:  BillyHvac replied 6 years ago.
3:35 PM

there is electricity in flame. Once the flame hits the rod it sends the milli-signal back to the control which says..."hey, I have some milliamps here so there must be flame." If the control is not fitted with a auxillary sense rod it does it through the spark cable back to control.

3:34 PM

That is why a ground wire is so important to these controls...without a good ground it does not sense the signal