[markjb]

Hi

When I power up the TCB the smoke output goes straight to full battery power and nothing I try makes it adjustable or turn off. I might have shorted out the two pins when I was checking the volt output so could this have caused damage to the smoker circuit. Everything else on the board works fine

[LukeZ]

Hi Mark, that is certainly strange behavior. It is unlikely you damaged the smoker circuit by checking the voltage, and anyway I assume you were checking the voltage because it wasn't working to begin with, so it sounds like the problem existed before you made the voltage check. Also, if we had fried a component it would be more likely the smoker wouldn't work at all, rather than go full speed.

Some of the Hobby King boards had outputs that were always on because they used the wrong MOSFETS, but this did not apply to the smoker output. It is still possible the problem is something physical with your board, and we need to figure out if that is the case, or if it is some kind of software problem.

Here is something you can try. On the Motors tab of OP Config, under the Smoker heading, change the control type from "Auto (with engine speed)" to "Manual (with function triggers)." Next, on the Functions tab, select "Smoker - Manual Speed" in the "Select Function" drop down, and then assign it some Trigger Source. If you have an analog aux channel on your radio, assign it to that. If not, you can just assign it to Turret Rotation as a test. Then click the Add button to add this function-trigger to your list, and write the settings to your model.

Now, perform a test - does the smoker speed change when you vary your aux channel, or when you rotate the turret? If so, we know there is nothing wrong with the hardware. If not, and it still goes full speed no matter what, it seems more likely there is an issue with the board, possibly a shorted pin somewhere.

Can you also post your OPZ file just so I can take a look? To save an OPZ file first read all the settings from your tank into OP Config, then go to File -> Save Settings to File, and then upload that file with your reply.

[markjb]

Hi Luke, I tried your settings but no change. I get about 4v when plugged in to my pc and 12v from the battery as soon as its connected. I have just been plugging in the smoke element as I want to run the fan from the aux port. If this can't be fixed is there another way to power the smoker for instance with a heng long proportional unit. Basically I just want full smoker power (with preheat ideally) on engine start for a few seconds and then shut the smoker down until next engine start. By the way the board has a 12v supply and the motors are 24v, it's a 1/6 scale tank.

[LukeZ]

Well unfortunately the indications we have so far point to a possible hardware issue. Thankfully the smoker circuit is fairly simple. I've attached an image below that shows the control pin on the processor and where the trace ends up at the smoker MOSFET. You might try to examine this trace closely, especially at the processor side, and make sure this pin isn't accidentally shorted to one of the pins next to it.

Another thing to try is to create a set of function triggers to simply turn the smoker output on and off. As before, on the Motors tab, set the smoker control to "Manual (with function triggers)." Then on the Functions tab, select the "Smoker - Manual On" function and assign it to one of your aux switches, and do the same with the "Smoker - Manual Off" function. Now that switch on your transmitter will turn the smoker output on and off (no variable speed).  Then while turning on and off the smoker from your transmitter, you can measure the voltage on the MOSFET pin (the one in the red circle at left). It should change from 5 volts to 0 volts.

Maybe you could also take a photo of your board and post it here so we can take a look just in case something stands out.

[markjb]

Hi Luke

I've tried the settings but it's still the same, it won't turn off. Here's a picture of my board, it looks ok.

[LukeZ]

Hi Mark, sorry for the slow reply, and thanks for the clear photo. You're right, visually it does look fine.

Would you be able to do the test described earlier?

Another thing to try is to create a set of function triggers to simply turn the smoker output on and off. As before, on the Motors tab, set the smoker control to "Manual (with function triggers)." Then on the Functions tab, select the "Smoker - Manual On" function and assign it to one of your aux switches, and do the same with the "Smoker - Manual Off" function. Now that switch on your transmitter will turn the smoker output on and off (no variable speed).  Then while turning on and off the smoker from your transmitter, you can measure the voltage on the MOSFET pin (the one in the red circle at left). It should change from 5 volts to 0 volts.

You earlier confirmed that the smoker output goes to full battery power, but I would like to know what the signal pin from the processor is doing, whether it ever changes (between 5 volts and 0) or if it too is always stuck high. You can put the positive lead of your voltmeter on the MOSFET foot circled in red in my earlier photo, and the negative lead of your voltmeter anywhere on the board that is a convenient ground (or connect it to your battery negative).

[markjb]

Hi Luke

The volts stay at 0 all the time, I have attached the settings for my tcb for you to have a look at. I've tried various triggers, these are the last ones I tried.

[LukeZ]

Well that's very strange, since if the pin from the processor is at 0 volts, the output of the MOSFET should be off. It can be hard to get a good reading sometimes, it seems like you really have to jab your multimeter probes hard into the surface, which then of course risks slipping and shorting something.

If the input from the chip is really 0 volts and your smoker is still running, then we can conclude the MOSFET is bad and would need to be replaced. It can be done by hand if you have some soldering experience, a good iron, and some flux would really help with the removal as well. Putting on the new one will be much easier than taking off the old one. If you're not entirely confident about it, I'd recommend against the procedure because it is certainly possible to make things worse.

The MOSFET part number is FDD8780. It doesn't look like Farnell UK has it, but it's still available from DigiKey in the States. They ship abroad but I don't know their rates. I also just did a quick search for FDD8780 on the UK eBay and I see several listings.

[markjb]

I'm sure my readings are correct but I won't risk any soldering so I think I'll just have to accept how it is. Not a problem though the rest of the board works great and I'll just find another way to control the smoker. Thanks for your help.

[LukeZ]

Ok, that is probably wisest rather than risk making things worse. I'm sorry this one has given you problems. There were some quality control issues with the Hobby King boards but this is the first I've heard of anything related to the smoker.