4.3 issues that have me pulling what little hair, I have, out.


 
J

John Bostwick

TVWBB Wizard
I been having lots of issues soldering these 4.3 boards, for some odd reason. My problems all deal with bad temps on the thermocouple. I have been getting 217°f at boiling water. Not just one board, but 3 boards. The last board I been trying to figure out, is actually reading a temp of 868° at room temperature. I been able to fix two of the three boards.

I had a 4.2 board that had perfect temps, and after trying everything else, I changed the atmega chips and sure enough the temps were perfect. And I put the bad chip into the good 4.2 board and it was 5° over at boiling.

I recieved some new atmega chips and some ad8495 amps and they have not helped.

I checked for shorts, bad solder joints, and reflowed solder joints, usding a reflow solder gun. I checked my components and that's one thing I'm having a problem trying to figure out if I accidentally mixed up my 1n and 10n smd caps.

If I did mix up my 1n and 10n caps what would happend? Would it make a difference in temperatures. I'm going to solder another base board today, and hopefully this one turns out better.

I have rambled on enough, been up since 1pm yesterday, time for some bed, lol
 
Mixing the 1nF & 10nF caps shouldn't change the measurements that much, or really at all. It would change the noise rejection filter cutoff frequency some. But that filter is really there for RF type frequencies, with the cutoff in the kHz range either the right or wrong way. It is getting colder out which means more ESD, maybe things are getting inadvertently zapped?

Do the other probes work fine, and just the thermocouple off? If so - that should eliminate the atmega, and put the focus on the AD8495 and surrounding components.
 
If the temp offset followed the ATMEGA chip to a previously working board, you would think that there's a config value set that is creating the problem. On the v4.3 board I built, I had a problem with one of the food probes reading high. It turned out to be a bad 0.1u filter cap. My guess is that I ruined it by pumping too much heat into it during the soldering process. One of my observations of the v4.3 boards is that the copper ground plane seems to be sucking up a lot of soldering iron heat.
 
Yeah, chock up the heat issues to "used to designing boards for production lines and not for hobbyists." The wagon wheels are thermal relief around the ground plane, and are supposed to help. Be generous with the flux, and get a large glob of solder on the iron before touching. The glob adds thermal mass, and helps to get a rush of heat local to the solder joint before it can start to spread out. Solid ground planes are good for low noise, but bad for solderability - it's a trade off.

I know Bryan was doing some work with the thermal calibration in a relatively recent code releases. Do you have the same version of code between the two Atmegas?
 
I'm pretty sure it's the atmega chip. After I recieved new chips, I have not had the same problem. But, it's probably due to heat, as I just recieved an resolder station and may have applied to much heat.

All is ok now,
 
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