Your voltages seems perfectly fine. Only R55 separate U17:6 with ADC input, but it's unlikely the cause of the problem.
Based on this, I measured from r55 to u5, and found a few ohms of resistance. Reflowing all of U5 seems to have fixed my problem. With no resistor, adc is steady 1023, and R is steady 2087. Room is steady 24.
With resistor, I have adjusted it to 1000, but the last digit still fluctuates rapidly (999 to 1001). If touch the board by the edges, the number drops to 991. Is that normal? Or is there still an issue?
Spiftacu1ar, can you check -0.6V at U18 and U13 , also at your picture is not good visible b/n caps C36, C37 and ADG734 for a left residue of a flux
U18:4, U13:4, and input at J9 are all -0.683. However, if I unplug J9, the input power changes to -0.589v. I suspect something might be wrong here?
Also, the new meter came in the mail today. I am measuring 2.8mv where expecting 3.8mv (measured 0.004v or 4mv on old meter) If I remove 10ohm resistor, I get ~343uA, consistent with my measurement with 1k resistor.
I took the pictures directly after reflowing, but cleaned the flux before powering it on.
Try to adjust the current by up/down buttons in the calibration menu and check if voltages changes accordingly. Check reference voltage on C44, should be 3V.
C44 is measuring constant 3.000v
I took all the measurements with the 10ohm resistor, and with cal menu current set to 64 and 256 (128 column is copy from before). '~' means that the measurement is still fluctuating, but I took an approx number in the range.
Which voltages would I expect to change when I adjust current? I'm guessing the the 3.8mv should scale with the the current? (e.g. if I go from 128 to 64, I would expect to see 1.9mv?)
To short a bit the efforts, measure Vtemp (Volt. drop over C65), the time you turn the RC2 and just to be sure same procedure at C62, while is connected calibr. R and you are in calibr. menu
I did this with only 10 Ohm resistor in place (Vout1- to SenseA), and in cal menu: Rc2 full counterclockwise: C65: 0.102v steady C62: 1.23v-1.30v fluctuating
Measuring fluctuation between ~0.327v and ~0.347v (hard to read, because the number is changing pretty fast) across a 1k resistor (measuring 998ohms on my meter) between Vout1- and SenseA.
First off, thank you all for the support! This morning, I have reflowed u10, u11, u12, u13, u15, u16, u17, and u18
U15-5 is now reading 3.154 Vcc is 3.267
I have followed the layout here: https://5n44p.github.io/unisolder-chips/ so I am pretty sure they are installed the right way. I have uploaded images of the resistor placement and cal screen.
Turns out my ability to count is bad. I was probing the wrong pin before. U10-9 is fluctuating between ~2.71v and ~2.75v, which is a little different than expected, but I think maybe close enough?
Drop across R34 is 2.047v, which seems pretty accurate.
U15-5 is fluctuating between 0.7 and 0.75, so I guess I need to look into u16, u18, and u13a per sparky's comment I quoted above. I'll start by reflowing those.
I just finished assembling my boards, and am having some issues with the calibration step. I have a 10 ohm resistor between SenseA and Vout1-, but no matter how I turn the cal pot, R value remains around 180, with the last digit fluctuating rapidly. Moreover, after being on for about 5 mins, I get a power lost message, it reboots, and then it reboots every few seconds (and get progressively faster). On page 35, I found someone with a similar issue (sans the power loss after a few mins).
Sparkybg had responded with the quoted message. So far, I am unable to measure 383uA, due to not having a multi-meter that measures less than 1mA. However, at U10-9, I measure 3.27V, so that seems wrong. Vcc is measuring at 3.27v, so U10-9 should be Vcc-0.625 =~2.65 if I understood that correctly. Sparky also mentioned U12A, Q21, Q22, and D19, but I am not sure what I should be measuring at these. I have tried re-flowing U10, but have not tried anything else at this point.
Remove the resistor and measure what current flows between SENSEA and Vout1-. It should be around 383uA. It if is not, you have a problem with current source (U10-9 should be around Vcc-0.625V, U12A, Q21, Q22, D19).
If it is 383uA, remove the resistor and the ADC should be 1023. It it is not, you have a problem on the signal path from SenseA to the MCU (either short circuit to ground or defective chip). Measure the voltage on U15-5 - if it is a little below 3.3V, the problem is with U15, U17, U11 or around them. If it is close to GND, the problem is U16, U18, U13A or around them somewhere.
For some additional background, prior to this, I had an issue where the board kept rebooting after ~0.5s with status 21 and power lost message. Reading through the thread, I found some information about ZD1,2,4 being 4.2v zeners instead of 3.3v zeners. My zeners had the same marking as the other people, and was also dated back to 2015, so it seems I had the same batch of mislabeled parts. All 3 are replaced now, and it boots and shows AC at the bottom right.
