New build - working with a few issues


 
J

Justin F

New member
Finished my build - all seems to work except a few issues:

* Probe ports 1, 2 and 3 (which has the ambient temperature on it) all work, but probe 0 doesn't work at all. Checked all the solder points, swapped out the probe from a verified working probe on port 1 to port 0. Never anything except "No Pit Probe". What solder points should I check and what else could be causing this? How can I troubleshoot this?
* I have 2x ET-732 probes. They don't seem to work unless they are plugged in half way and never below about 90deg. Is this expected? What would be better probes to buy that work to colder temps and can be plugged all the way in and work to colder temps (meat often goes on at 60-70deg)?

Feel like I am almost there! Thanks for all the help and direction - super excited to get this working.

-Justin
 
1) Looking down from the top of the board (solder side), check the voltage on the top right pin (28) of the ATmega chip. With nothing plugged in, this should read 3.3V. When you plug the probe in it should drop to a value that represents the temperature. If it does, verify your coefficients are set properly for the ET-732 probe. Also make sure it is warm enough to get a reading, see below.

2) The ET-732 probes bottom out around room temperature when used with the standard 10k offset resistors. See the Wiki. You can replace your 10k resistors with a higher value to extend their range. The plugs being slightly longer than the ET-72/73s-- there's nothing I can do about that but you can mod the plugs to make them work a little better.
 
Bryan Mayland said:
1) Looking down from the top of the board (solder side), check the voltage on the top right pin (28) of the ATmega chip. With nothing plugged in, this should read 3.3V. When you plug the probe in it should drop to a value that represents the temperature. If it does, verify your coefficients are set properly for the ET-732 probe. Also make sure it is warm enough to get a reading, see below.
Click to expand...

Thanks for the quick reply!

* I've checked to make sure that the probe is warm enough (put it in hot water) as when I plug it into another port, it works.
* I've checked the coefficients are set to the presets for a Et-732.
* I'll check the voltage - if I don't see the 3.3v or don't see a drop, what would be the next steps to fix or troubleshoot?

Any other ideas?
 
if you don't see 3.3v at pin28 with the probe uninstalled, check R18 installation. you should see 3.3v on both sides of it.
 
It is the resistor on the top right of the ATmega chip, the 10k resistor closest to the probe jacks. If it doesn't go down when you plug in the probe, the jack itself might be physically broken and not making a connection. Without a probe the left and right pins of the probe jack footprint should read open. When you plug it in, it should get resistance.
 
Bryan Mayland said:
1) Looking down from the top of the board (solder side), check the voltage on the top right pin (28) of the ATmega chip. With nothing plugged in, this should read 3.3V. When you plug the probe in it should drop to a value that represents the temperature. If it does, verify your coefficients are set properly for the ET-732 probe. Also make sure it is warm enough to get a reading, see below.
Click to expand...

I checked this today - actually measured at the probe jack. All the other ports give me 3.3v but the one in question gives me 1.88v. Any ideas?
 
Also - when I take voltage readings across the R18 resistor, I see about 1.4v, whereas the other two that are reading correctly show 0v.
 
There's something connecting the output of R18 (the half closer to you) to ground, through ~8.3k ohms of impedance. That could either be something connected to the left pin of the probe jack (the pin on the back of the jack), or to pin 2 of the pin header marked PROBE, or maybe the jack itself has something in it that's making contact. There's not a whole lot of circuit between there and ground so there's not a whole lot to check:
 
Dave Pike said:
if you don't see 3.3v at pin28 with the probe uninstalled, check R18 installation. you should see 3.3v on both sides of it.
Click to expand...

Just checked - I get 3.3 volts on the input but only 1.8v on the output - could the resister be bad?
 
Last edited:
Probably not. Voltage drops over a resistor proportional to the amount of current going through it. If there's no probe plugged in, there's no current so you should see 3.3V on both ends. However, if the output side is making contact with something in the pink area I circled above, then current will flow and you'll see a voltage drop.

Because it is 1.8V, we can tell the resistance of whatever it is connected to is ~8.3k ohms, so it isn't a short, and it isn't connected to the next resistor over. That's all I can tell though.
 
remove the probe jack. look for any solder bridges. look on the jack also. test board. with no probe and no current, the voltage on each side of r18 should be 3.3v, and zero voltage when you read across r18 directly (this is a recap of the msgs above). if there is voltage across r18, which side is the + side (just for verification)? also, there are some probe takeoff locations on the board that do not connect to the jack. make sure those do not have a solder on them. if all these are in order, I am wondering if removing the avr might be in order to verify if it is the one pulling down the one side of R18. a reflash or replacement might be needed then. try a reflash first.
 
Bryan Mayland said:
Probably not. Voltage drops over a resistor proportional to the amount of current going through it. If there's no probe plugged in, there's no current so you should see 3.3V on both ends. However, if the output side is making contact with something in the pink area I circled above, then current will flow and you'll see a voltage drop.

Because it is 1.8V, we can tell the resistance of whatever it is connected to is ~8.3k ohms, so it isn't a short, and it isn't connected to the next resistor over. That's all I can tell though.
Click to expand...

First off - thanks again for all your help. I really appreciate it.

I have tried to re-solder R18, look for any connections in the pink area and am stumped. Hoping you guys could take a look at the pictures and see if you see anything I don't. Again - sorry if this is to amateur for this group - i'm new to this :)

IMG_3103.jpg

IMG_3104.jpg


Thanks again - can't wait to solve this last issue and get my first cook going!
 
More info -

When I read resistance over the resistors, starting at R18 (working my way down the line, starting at the resistor closest to the probe jacks) I get 116k, 10k, 10k and 5k. Also, voltage on pin 28 of the ATmega is identical to the output of R18 (think this is to be expected). At this point think I need to start tearing down the board, starting with the probe jack. Don't see any other bad connections...other ideas? Shouldn't resistance over R18 read 10k?
 
In-circuit resistance measurement is *usually* never valid, because resistance measurement is done by the instrument being a current source, and everything else in the circuit can effect the measurement of the subsequent reading.
 
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