Q1 was dead as a dodo once replaced everything went alive.
thx xystwr as advised I focused on REF3030 and "bingo" one of the solder joints was not giving correct contact. Now it is showing ACF. Calibration went smooth no issues.
I wired up my C245 handle and inserted my test tip and I am getting message that heater is open. I checked continuity between V1- and V1+ on my connector and this is correct. Any hint where to look for fault? I will be very grateful.
PPS: ZD3 is in wrong package!!! You should use a zener in SMB package. The one you used is too small and low power. I cannot be sure that the problem is there but it is in wrong package anyway.
I noticed this during assembly but this error comes from existing BOMs as they list this package as SOD123 same applies for ZD1 ZD2 and ZD4 they point towards SOD323. My current ZD3 is SZMMSZ5258BT1G and 3V Zener is BZX384-B3V0.115
I would be more then happy to replace them to correct package but I am not sure if what I found will be adequate. ZD3 - Z2SMB36 ZD1 ZD2 ZD4 - BZT52C3V0
The oscilloscope need to be isolated if you have connected the EARTH from the mains plug to anywhere. Did you?
And what problem do you have on J3? There should be 3.3V, -0.6V and GND there. Do you have these voltages there?
Make a detailed picture of your back board around U1 and Q1 please.
Thank you for your support on troubleshooting this issue. On the very begin before I attached a front PCB I measured a voltage to ensure J3 pins gives correct voltage. Everything was fine until yesterday. From unknown reasons voltage is no longer there. Q1 needs replacing as I do not like a slight crack in the middle of this component. Picture of my U1 section below . Forgive me exposed mask but tracks are still fine.
Faulty Q1 won't lead to DC detection instead of AC. By all means, you have fault there, but you have also fault elsewhere. Unfortunately without oscilloscope it is extremely difficult to say where it is.
Basically, in order to detect AC, the voltage after rectifier diodes is directly fed to a voltage divider R43-R43, limited by ZD4, and filtered by C60. The voltage on C60, which is rectified sinusoid, limited to just above 3V, is fed directly to the MCU pin, where the MCU comparator reads it. For some unknown reason, you either have a DC voltage on C60 instead of rectified sinusoidal voltage, the plateau voltage there is above the comparator's reference point, or the comparator itself is not functioning properly. This leads to a constant high level of the comparator and the MCU thinks that there is a DC voltage on the input power port.
I might be ale to put my hands on oscilloscope at my workplace so once I will fix J3 power issue I will give it a try.
I mean he put a very little effort in debugging still and this should be an easy power thing. And you advised to spend $100 on top of already spent $80 or so and throw those $100 in the bin.
I would follow the power path, starting from AC voltage after the fuse. May be measure voltage drop around R9, check R47, R51 divider resistance. The problem with incorrect zeners was already discussed and solved here.
Thx for support. I did not see much of a benefit of moving parts to a new PCB either as the fault is within some components. I personally prefer to document this kind of issues and troubleshooting in this thread as this can help other people in the future. I done some more diagnostics but I stopped getting correct voltage on J3 and zener diodes voltage on ZD2 ZD1 is to low. I suspect faulty Q1 FZT605. I will give some more update once replaced. Once again thank you for support.
...but this is why it detects DC. The threshold fro detecting AC is 5.625V, and you have minimum over 7V.
Replace ZD1 and ZD2 with the right zeners. Replace ALL 3V zeners, with the right ones. Obviously they gave you 4.25V zeners instead of 3V.
Thanx for your help. This component definitely seems to be iffy.
I removed ZD2 to double check voltage as part seems to be correctly marked. I verified this with 1k resistor and 5V power source measured voltage on this component is 4V.
Looks like I will need to wait a week to get the replacement parts.
Looking good Vulkan35. I found one more case that is suitable size. I am planning to replace front and back panel with transparent acrylic sheet. I need to wait for delivery to confirm panels dimensions. In the meantime I am looking for someone able to make some laser cuts acrylic sheets for me.
I replaced U3 chip today and unfortunately I am still not able to calibrate my station. As mention before I power my station with 24V 5A AC but station shows DC. Any ideas what else should I check.
