Strange lid detection problem with HM 4.1


 
T

Tom Kole

TVWBB Pro
Last night I started a cook with my new HM 4.1. I was running in fan and servo mode over cat5 and started getting some very strange behavior. I initially had the fan and servo both operating together with fan from 10 to 100%. At first everything was ok, the pit was stoking at 100% and I was ready to go to bed. But then something strange started happening. As the pit got closer to temp and the blower speed was decreasing, the HM kept going into lid open mode. I tried manually exiting but it would always go back in. As soon as the requirements were 100% again it would come out. But as soon as it started dropping, the behavior would happen again. It appeared to happen once the blower speed reached the min % of the blower, in this case 10%. So I started raising the min blower speed and it seemed to follow what I was doing. I tried reflashing the firmware but no dice. I ended up just putting it into fan on/off mode just so I could go to bed. Any ideas what might be going on?
 
Thanks! I forgot to mention if I unplugged the cat5 cable during this lid detection problem, it would come out of it.
 
Do you think it may have something to do with the shared ground between the fan and servo? Though if that were the problem, I'm not sure why it would have no impact at 100% power.
 
I'm not sure at all. I think if that were a problem you'd see another manifestation of the issue as well, like the temperature would change or something. I still need to reproduce it to be able to narrow it down.
 
I can't reproduce this at all, at least with thermistor probes. The only time I get lid detect coming on is when it is actually supposed to. I also examined the code and it doesn't look like there's any reason this should be happening unless it achieves temperature then drops back down below temperature more than the configured amount. Any other ideas?
 
I've been working on this all morning. It has consistently been happening for fan power below 20%. It goes into lid mode and if I manually exit, it goes right back in. If I unplug the cat5, it stops. If I set fan to max only, it stops. I've tried 3 different RTD probes and 2 different cat5 cables, all the same result. I just don't understand how the low fan power could trigger a lid detect. Maybe I'll try resoldering the pit probe jack, maybe there is some connection problem causing a reading that I'm missing to trigger a lid detect? But if that were the case, I would think that I should see the temp deflection on the graph. I'm stumped.
 
I've been experimenting some more with this. I took the HM and set the temp to just above RT so that the blower speed would be under 10% and the problem happened again. This time I had the HM on my lap so I could see what was happening. As soon as the fan turned on, the screen flashed no pit probe and then came back. The unit immediately went into lid mode. See graph below. I then started raising the setpoint temp to increase the blower power. You can see that this kept happening until I get to a blower speed of about 65%. At this point it behaves normally. So there is something triggering a no pit probe at low blower speeds with my HM.

11916158673_2a836a58e5_b.jpg
 
Oh that sounds like a power problem right tharr. When the fan first ticks on, it runs at 100% for 125ms and it looks like that's causing power to dip and cause the probe to drop out.

Is this with the standard blower with a 1A power adapter? You might also double check your electrolytic capacitors to make sure one isn't backwards or something causing it to not perform well.
 
Yeah, standard 1A power adapter and blower that I've used with previous versions. So I should focus on those 4 capacitors just behind the cat5 jack?
 
Yeah check those 4. They should all face the same direction with the negative stripe on the RJ45 jack side. The blower power circuit is different than in the v4.0 version but I wouldn't think it would make that much difference.

If you want to set up your HeaterMeter on the internet (with the blower hooked up) and email me the address and password, I can also take a look at it from the software side and see if I can diagnose exactly what's going wrong there.
 
Cool. I checked them out last night and they are all facing the right direction. The solder points looked solid. I'll get it setup tonight on the internet so you can check it out. Thanks
 
I've been working with Tom on this and we've found that the issue seems to be stemming from a ground noise issue caused by when the blower is running. The noise is high enough to trigger a "left" button press event which turns on lid detect mode. Tom worked around the problem by soldering a wire from the blower pin of the RJ45 connector to the ground pin of the power input jack.

Work on fixing the cause of this is ongoing.
 
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