Troubleshooting help


 
B

BrentV

New member
Hello all,

So, being the genius that I am, I left my HM 4.1.4 out in the rain after my last cook. That killed the Raspberry Pi and left some corrosion on the HM PCB. I dried everything out, replaced the Pi and cleaned up the HM with solvents, and now it works - sort of. The switch on the HM does not seem to work correctly and my Vishay 10k ambient temp sensor is off by like 20+ degrees, in spite of resistance being in the 8k range, which matches a spare one I had hanging around. I know this could be a lot of things, but does anyone have any suggestions for how to troubleshoot this?

Thanks,

Brent
 
The vishay is probably reading off because it is connected through a switch inside the probe jack, being out in the rain it probably got wet and is either still wet or a bit corroded. Blow out the probe jack to make sure there is no water in it and then insert and remove a probe from that jack a few times to operate the switch and see if the ambient temp doesn't come into line.

IDK what to say about the switch other than check the traces are still intact after the corrosion and board cleaning, or maybe the switch took on water too? I've never really looked into the switch circuit before, it looks pretty simple....

There's 4 resistors that go between the switch and 3.3v supply, so four of the resistors should have 3.3v on one end and connect to the switch on the other, the COM leg of the switch has a 1K resistor to ground.

The COM from the switch goes to Pin 23 of the ATMega, so you can check continuity between Pin 4 (COM) of the switch and Pin 23 of the ATMega.

Since each resistor is a different value (and all connected to 3.3v) when you put the switch in different positions the COM leg of the switch should show the voltage associated with the value of the resistor connected to that leg of the switch.... 4 positions, 4 voltages. Should be easy to test and trace.
 
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Ralph,

Thanks - I dried it out, then gave it an alcohol bath, which should have 'dissolved' any remaining water, then blew it off with low pressure compressed air. Traces are intact under microscope inspection. I think I'll start with checking the switch for correct operation and work outward from there.
 
Short out the back two pins on probe 4 (where the ambient temp thermistor is connected) and see if the temp is correct then. If so, then the switch in your probe jack is the issue.
 
Shorted the pins and the temp was correct. I'll replace that jack (ugh, desoldering) and I'm working on testing the switch right now.
 
Update: used a little shot of solvent and plugged a probe in and out a few times and the ambient temp sensor worked again. After some testing, I saw that the switch was not working. Lucky for me, I ordered a few extras of those 4-way switches before they were EOL, so I was able to replace it and everything is working again. Thanks, Ralph, for all the help.
 
Glad to hear you've got it all dialed in, good call on ordering the extra switches, I have a few here myself for that same reason....
 
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