v4.0 Blower Circuit Troubleshooting


 

TB Gallant

TVWBB Member
Hey guys,

So have my old v4.0 board working pretty good except the blower doesn't work. I tested it by hooking it up direct to 12V and works good so must be something on the HM side. Some things I've tested so far:

- checked the various 5V and 3.3V on the HM board using an old diagram I found. Some of the 3.3V locations are a bit 'low' in voltage (2.9V and 2.8V on RX and TX I think) but otherwise all good.
- checked the +12V pin on the blower J4 and it is 12.5V
- when I first power up the HM/Pi (Zero W) the output on the blower starts high (closer to 12V) but then consistently drops to essentially nothing, 0.16V or so. This must be a clue but I'm not electrically intelligent enough to know what it tells me
- the center pin of the FDP7030BL does seem to 'pulse' to ground (check ohms between ground and center pin, goes from 1 (infinite) to some other value, back and forth cycling)

I know that this old v4.0 setup pulses the blower ground, but even with the fan output stating 100% the same symptoms happen above.

Appreciate any help someone may be able to offer for this ancient board.

Cheers,

Tim
 
When you say the blower voltage starts high when powered up, then trails off to 0V, is this measured from the blower ground (which is pulsed) or from a true ground? I am trying to figure out if your 12v supply voltage to the blower circuit is going away or if the ground is causing the voltage to trail? I would check the 12V supplied to the large MOSFET measured from ground at the power jack to confirm if it is steady or falls off?

Beyond that, the most common causes of blower circuit failure would be a blown BS170 (which may be a different model transistor on v4.0, I don't recall, at any rate, the small transistor in the blower circuit) or a solder bridge at the large MOSFET, or sometimes not flowing solder to the other side of the board to make the part of the circuit that is laid out on the top of the board.
Also, make sure you have the blower set to PULSE mode in the HM config, 'cause v4.0 does not have the feedback circuit required for voltage mode.
 
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When you say the blower voltage starts high when powered up, then trails off to 0V, is this measured from the blower ground (which is pulsed) or from a true ground? I am trying to figure out if your 12v supply voltage to the blower circuit is going away or if the ground is causing the voltage to trail? I would check the 12V supplied to the large MOSFET measured from ground at the power jack to confirm if it is steady or falls off?

Beyond that, the most common causes of blower circuit failure would be a blown BS170 (which may be a different model transistor on v4.0, I don't recall, at any rate, the small transistor in the blower circuit) or a solder bridge at the large MOSFET, or sometimes not flowing solder to the other side of the board to make the part of the circuit that is laid out on the top of the board.
Also, make sure you have the blower set to PULSE mode in the HM config, 'cause v4.0 does not have the feedback circuit required for voltage mode.

Thanks for the reply Ralph. To confirm, the voltage drops only when I start checking it with the DVM between the blower jack "+12V" and the ground pin on the jack. The +12V pin/hole in the board stays constant at 12.5V when using another board ground with the DVM. Another 'symptom' is that even if I leave HM running for a few minutes upon start up, when I first check the blower voltage (using the +12V and the blower jack ground) it starts at ~ 12V and only starts dropping when I use the DVM. Almost like it only drops when there is a 'load' on it (if that makes sense)?

I don't see a transistor in the blower circuit on v4.0 (but I don't really know what I'm looking for). I'm using this trace picture of the board:

http://capnbry.net/linkmeter/pcb/hm-4.0/HeaterMeterPI-brd.png

So I'm guessing it is the MOSFET? I resoldered all of the pins on the blower circuit without any change. They all look pretty good to me. Not sure how I can test it.. so I guess I just have to buy a new one? Try and track it down locally to save crazy shipping.

Cheers,
 
It has been a while since I've looked at a 4.0 board, but the circuits are completely different from the current 4.2/4.3 design. I do know that you can't measure the voltage on the blower's output directly-- the ground pin on the blower jack is not ground. I've spent a good 15 minutes staring at the 4.0 schematic to try to figure out how to troubleshoot it. I dug through the boxes of HeaterMeters I have and was shocked to find no working 4.0 setups, I think I gave away my working 4.0.

Before any of that, can you verify that in the webui configuration you've got the blower output set to PULSE mode (not Voltage), on above 0%, min 10% (shouldn't matter), max 100%, startup max 100%, invert output not checked.

Set the setpoint to 0% (manual mode), no blower connected. Short the two blower pins together with a piece of wire or something and then measure the voltage on the capacitor right next to the BLW pins. With the BLW pins shorted, you should see your full 12V on that capacitor. Now REMOVE THE WIRE SHORTING THE PINS and set the setpoint to 100% (manual mode). Measure the voltage on that capacitor again, it should drop to 0.000V and be steady as a rock. If the voltage is still slowly dropping, then the MOSFET isn't on properly. Check the pin on the MOSFET furthest from the board edge (closest to the boxy robot logo) and it should be 3.3V steady, measured between that pin and a real GND, like the power input jack.
 
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