Fan stuck on high


 

Wayne Ficklin

TVWBB Fan
I've got a set point of 2ºF and my thermocouple is showing 70-ishºF.

The display shows that the fan is off, but its wide open.

A little back story, I melted my previous cat5 cable so that when it was plugged in to my HM, it wouldn't boot. Take it out and it booted up fine. (It took me a while to realize that.) I found a new cat5 cable and wired it up, except I wired black to blue-white and red to blue (which I've since seen is backwards and fixed, since the fan wouldn't come on wired backwards.)

Now I'm stuck with the fan on with no control when its plugged in to the HM rj45 jack.

Any pointers?


http://ficklin.afraid.org:5000
 
Last edited:
I would check continuity on the wires you are using for the blower to the pins on the HM board, GND and BLOW, make sure you have the right wires first.

Here is the blower circuit schematic with some notes

HMv4.2_BlowerDriver.jpg
[/IMG]

Here is the HMV4.3 board with a few notes about the blower component location

HM_Blower_Notes_V4.3.jpg


Here is the v4.2 board with more notes, blower circuit is the same but component location is diffrent that on v4.3

HM_Blower_Notes.jpg


Since you said you melted the original CAT5 cable that seems like you make have shorted the blower wires, in which case the part I would suspect of blowing would be Q3 (the large mosfet). If this is blown I would suggest you also replace L1, the inductor is hard to test unless you have a good multimeter with an ring tester for inductors. The last HM I fixed that had a blown Q3 also damaged the inductor.

You should also change the blower config to Pulse mode in the HM config and see if the blower works then, that would indicate Q3 is good and the feedback circuit is damaged (likely L1).

Good luck with your repair.
 
First off, thanks for the response and the helpful diagrams.

With my black lead on the "blow" pin of the rj45 side of things, I checked continuity/ohms to c12, the first side of L1, the other side of L1, back to Q3's middle pin: 0.000 ohms.
With black lead still on the "blow" pin, I went back to the first side of L1, then this side of R13, then that side of R13, and up to the 22kOhm restistor above it: 0.000ohms.
Red lead on red wire @ fan, black lead on blow:0.000 Ohms
red on black wire @ fan, black on gnd:140 Ohms

red on blow, black on gnd (rj45 pins): 0 Ohms

Switching over to vDC w/ the unit powered own (that matters I found after realizing my testing power supply wasn't turned on):
With my black lead on the left Q3 pin and red on the bottom right Q1: 0v
with my black lead on the right Q1 pin (GND) and red on the middle Q3 pin: 11.55v
With black on rt q1 and red on right Q3: 11.55v
With black on rt q1 and red on left q1: 0.001v
With black on rt q1 and red on top q1: 0.001v


One other thing that was peculiar: Without the rPi connected, and right after I connect power to the HM, I noticed that it sounded like the fan was ramping up. I checked the voltage across the fan and it was around 6.5v and went up to about 9.

Then I hooked up the rPi, and it went full speed. I'm also noticing that the mounting hole on the pi nearest the sd card is really hot. Also, I'm having a hard time connecting to the rPi, so I might need to try a new one of those.
 
Hard for me to follow the data in your post. I am going to give a general rundown of how I would troubleshoot the situation because that is easier for me to do.

First off, regarding the comments about the rPi being connected or not. Is this a working HM? (meaning, when powered up does the display show you information like probe data, menus etc?) If it is a working HM you don't need the rPi, the HM will work on its own (the rPi essentially provides the web interface, and initial programming of the ATMega). That said, if the rPi is working and you can connect to the HM web interface I would suggest you log into the HM config page and set the blower mode to PULSE (rather than voltage). Reason being, voltage readings can seem a bit wonky in Voltage mode, it is easier to diagnose the blower circuit in Pulse mode.

If you set Pulse mode and the blower suddenly works properly then you have a problem in the blower feed back circuit. Post back if this happens so we can go down that road.....

After setting Pulse mode you can power down and disconnect the rPi to eliminate any possible effects it may have. While testing connect the HM alone, use menus to change fan to manual mode, then use buttons to ramp blower % up and down to test.

The first thing you need to do is see if the two transistors in play here (Q1 & Q3) are biased properly.

Set your HM to 0%, put your meter to VDC with the black lead on GND (at power jack) and then with the red lead measure the voltage on the center pin of Q1 (should be 0v) and the left lead of Q1 (should be 12V). Also confirm that you see the same voltage (12V) on the right pin of Q3.

Now set your HM to 100% and make the same measurements, the center pin of Q1 should now read 3.3v, the left pin should now read 0V (as well as the right pin of Q3)

The voltages you report from the above tests will tell what is going on here. The flow of the circuit goes like this, the ATMega puts out a voltage between 0-3.3V, that voltage controls the bias on Q1 which in turn controls the blower driver MOSFET (Q3).

Report back results of these specific tests and I will try to help you get this HM up and running...
 
Report back results of these specific tests and I will try to help you get this HM up and running...

Thank you for taking the time. It turns out that it was the RasPi. Replacing it and everything seemed to work.

(Also, this is the HM that I received where the screen doesn't work. I'd still like to get that figured out, but for now I've got a working HM + RasPi.)
 

 

Back
Top