I've done a few additional measurements, this time with a scope. And, by now I actuall tend to agree with both of you. All signals I measured look ok to me, everything points to a faulty MCU. First I did not believe it to be the MCU, because it was brand new, purchased at digikey or farnell (don't remember, but definitily either of the two), so I sure hope it's no chinese copy. Sadly, I do not have a replacement at hand right now. But, I wanted to order a few things at digikey anyways, so I guess I'll just get another PIC and try to replace it. Will report back to you guys as soon as I have my replacement and soldered it in place.
Again, heaps and heaps of thanks to you guys for bearing with me! I really do appreciate it.
Edit: For completeness sake: Yes, the voltage reference is rock stable at 2,978 V. It is a little less than 3 V, but I guess it's ok. It would only lead to a slight offset in the termperature measurement.
It should be logic "0" (at least less than 0.8V ) in cal. mode. That's mean firmware or U5
Yes, that's what I tought. As I said, it was either U5:2 or U5:3, after reflowing it works properly now.
The temperature now rises beyond room temperature, but it is very, I don't know how I should call it... jerky? It jumps around wildly, every now and then a realistic temperature value pops up on the display, but mostly it's rubbish. I've tried to capture it with the software by logging the data through USB, I've attached the screenshots. "Calibration.png" shows the data acquired in calibration mode. Looks very good. "wCartridge.png" shows the data logged during heating. And this is the one making absolutely no sense to me. The ADC value looks perfectly fine. The "Current Temperature", "Filtered Temperature" and "PID Temperature" on the other hand make absolutely no sense to me. How is it possible that they deviate so much from the ADC value's behaviour?
now, that is a very interesting thought, and it also seems to be the right place to start looking. Because, the voltage across C10 is 0,7 V, which in my opinion is everything else but close to 0 V. Tracing the problem back to the µC lead me to a broken pulldown resistor for U3 (R21 was bad). Replacing it did not change anything, but ONOFF seems to be having a duty cycle of 50% (at least the voltage of the ONOFF trace is ~1,7 V, measured at U3A:2 and U5:2).
As I am writing this, I reflowed pins U5:2 and U5:3. That solved the temperature problem, indeed. Now, onto the next problem: the lab supply I'm using seems to struggle with providing the required power. It did work in the past, it's specified for up to 8 A, but I guess that's a problem not related to Unisolder but rather something I have to solve on my end. The supply is like 30 years old... Will report back testing with a different supply.
For now I really want to thank you guys for supporting me and leading me to the solution!
so, I reflowed everything as promised the other day. But, no change, the temperature still is only room temperature. But, as an added bonus now the USB communication works, which previously did not work (found that out shortly before reflowing everything).
But, I have got an interesting change. Now the iron starts heating, even when I am in cal mode! Before it just showed me the TC voltage without heating. Now it starts heating the instant I plug the iron + cartridge in, no matter if I am in cal mode or normal mode.
Another very interesting thing I absolutely cannot make sense of is the iron ID. When I connect the handle only (without cartridge), it correctly shows 24 5 as IDs. When the cartridge is inserted, this changes to 24 8, even though "JBC C245" is still displayed as tool in the top of the display. And, as I said, it instantly start heating, even in cal mode...
What is left - U5 for a re soldering or a replacement
I completely resoldered U5, sadly without a change. U5 is brand new, I replaced it a week ago. I cannot replace it at the moment, because I do not have a replacement at hand.
Tomorrow I will reflow all components on the PCBs with a hot air soldering station, if that does not help I might retry using an reflow oven. But right now, I again am without the slightest clue, what might be wrong with the board.
I've just tried to heat up C245 with hot air @270*C and got ADC value around 250, maybe it helps somehow.
That helped tremendously, indeed! Thank you! Now I know the wiring is ok and the OpAmps work correctly. When I let the tip heat up for around 3-4 seconds, I get a similar ADC reading, slightly above 220, seems to be about right. So in my eyes now the wiring is ok, the OpAmps are all ok and the cartridge is ok.
kage-chan, try to check U13B or replace U13, check Vshunt line for a connection and proper soldering resolder Rs1
Nice idea. From Rs1 up to U5:12 every trace, solder joint and connector has continuity and a very low resistance (not measurable with my DMM). While heating up the iron, I can measure about 500 mV at C59 with my DMM in DC mode (yes, I know, wrong tool, but that's all I got at hand right now). So that shows me that the vshunt path is doing at least something. Next time I get an oscilloscope in my hands I'll try graphing the voltage at C59. In Cal mode all voltages along the vshunt path are zero in my case. To me, from the schematics it makes sence, but can somebody confirm that?
tried reversing the red and green wires ind the handle's connector, still, no change.
As for the FW, I am still using sparkybg's code from the original post, which hasn't been update for quite a while. Might that be an issue? You guys seems to be working on the FW...
It just came to my mind, I did modify the FW before, because I'm using a different display (SSD1603, twice the size of the original, had to flip text). I'll check with the original FW again, even though, I honestly don't think I broke it THAT much...
Edit: Ok, just tried the original FW from the first post without any modifications, no success either. Does anybody have a list of TC output voltages for different temperatures (including RT, please) for the C245 cartridges? And, can anyone point me to the place in the FW code where I can change the delay between turning off the heater and measuring the TC voltage? Would try increasing the settling time for the TC...
FW modification is required. Theoretically, only SChannel parameter of NO INSTRUMENT profile have to be changed to 2, but I didn't tried it. Both current source channels are set to 128, so calibration resistor can go to either. If you have some problems with ch. B ADC value would be close to its limits.
Thank you for the SChannel hint, I couldn't find any documentation of that parameter in the source code, it would have taken me a lot longer to figure out. Thanks!
And, senseB seems to be perfectly fine. When I change only the SChannel parameter to 2 and connect the 10 Ohm resistor between vout1- and senseB I get ADC values of around 999-1002 (exactly the same as with senseA). When I additionally change the heater channel to 1 and connect the resistor between vout2- and senseB I get 993-995. So an acceptable deviation. But, that in my eyes also shows, that the wiring is definitely ok, right?
Any other ideas what might be wrong?
I just noticed that my EARTH wire is not connected anywhere yet, it's floating. Wanted to connect it to PE later, when the PCBs are in an enclosure. I'm powering the PCBs with a DC lab supply at around 15 V. Might that be an issue? Just wondering...
It's because C210 TC is connected differently within cartridge. With C245, temp sensing is using both diff. amp. channels with ch. B going below GND, while calibration is done using ch. A only, probably the problem is with ch. B, i.e. U16 and surroundings. Is -0.6V rail OK? Having the ability to switch between channels in calibration mode will ease the input section troubleshooting.
Thank you for the clarification regarding the C210. I also do suspect channel B being not ok. U16 is more or less brand new. I replaced U16 before. Shortly after that, I realised that I had D21 and C64 shorted (GND pin of D21 to high side of C64). That should have protected the BCH input of U16 from any damags I guess. How can I test if it is ok or not? I do not have a replacement at hand. The -0.6V rail is at -0.67V, I guess that's ok? Is there a way in the supplied FW to calibrate Ch B?
that's correct for the molex, about mess with Vout2, if you have correct ID and the Fuse 5A wasn't burned still everything is ok, to be sure check R64 and D21 use 10 Ohm R when measure the input chain ( to have your hardware safe, the time you measure and your hands free ). Read and compare from page 190
D21 and R64 seem to be ok, as written above, there was a short, but it is fixed now. For channel A the values match up. Is there a way to do the same for channel B, without rewriting the FW?
I know I am a bit late to start asking questions, but I am really stuck on the last issue. I started building the station like a year or more ago and did not finish it. Now, I wanted to finish it once for all. I am using a JBC T245 handle on the station with a C245 cartridge.
I have read most of the posts in this thread, there also were a few other people with the same issue, but either they didn't post their solution or their solution does not apply to me.
Issue: When I power up the station with handle and cartridge connected, the cartridge heats up, the displayed temperatur is stuck at room temperature. But, aperiodically the displayed temperature jumps up to like 40 or 60 degrees, but still far from the actual tip temperature (after 3 seconds the tip temperature should be well beyond 40°C or 60°C I guess...)
What I have tried so far:
Calibrating works without an issue.
I have double an triple checked my wiring. I cannot seem to find a mistake or problem. Just as an additional information, I have no idea if it matters: vout2+ and vout2- were mixed up before, but they should be correct now. Looking from the top on the Molex connector for the iron power: top left: vout1-, bottom left: vout1+, top right: vout2-, bottom right: vout2+. Could anyone please confirm this?
When in calibration mode and the tip + cartridge are connected, I do see an adc value. For room temperature it is barely above 0 (single digit), if I heat the tip up with a different soldering iron the value will rise. So I guess the TC in the cartridge is ok.
Its hard to tell, but when measuring the voltage at U16A:2, it seems to not rise above 153 mV. As I said, I'm not 100%ly sure about this one, because it's hard to measure only with two hands and an heating element running wild... I have not tried replacing D20 and C63. Maybe I should? But, I also assume that the 153 mV are due to the heating, and not due to the TC.
When powered down, Q2, Q8, Q10 and Q11 seem to be ok (few MOhms between D and S)
Obviously, tool detection works properly, if no cartridge is inserted into the tool, I get a "HEATER OPEN" message. The tool is correctly shown as JBC C245
I have not tried reversing the TC polarity on the connector. But, I also haven't found the reason sparkybg gave why it should not be connected the other way round, like for the C210. Can anyone point me to a answer there?
Any help is welcome to solve the issue, I am stuck for days now, this seems to be really the last issue I am having, I am out of ideas right now.
I am able to compile the FW, so if you want me to change things there to try something I could do that.