Late response... had little time past week. Today I have measured U at R11 as requested. I tried with AC and imagine my surprise when the controller was working. At that point, I had not put back D12 and R9 yet. And I guess last time I did not test on AC because it was not working on DC. The problem with DC is my lab PSU, which I think trips out at the current spikes. I then put back the diode and resistor to test my theory and yes! It is no longer working. This means I have a problem in the power factor correction circuit. Just need to find where.
Hello! I figured out the problem. My ZD1 and ZD2 were 4.2V zeners. I had to replace them 3 times before I got the correct values. I ordered from Mouser. It scares me that you can get the wrong parts 2 times in a row. Different order dates and different part numbers. The webpage contains false information (serial number) stating they are 3V zeners and you can not help yourself with the datasheet (because of the wrong serial number). Anyway, the station is now working and I enjoy working with it very much.
Late response... had little time past week. Today I have measured U at R11 as requested. I tried with AC and imagine my surprise when the controller was working. At that point I had not put back D12 and R9 yet. And I guess last time I did not test on AC because it was not working on DC. The problem with DC is my lab PSU, which I think trips out at the current spikes. I then put back diode and resistor to test my theory and yes! It is no longer working. This means I have a problem in the power factor correction circuit. Just need to find where.
I've attached images of the boards and oscilloscope signals. Images are named after signals they are showing.
You can see there are spikes on the Vin rail, every time the controller turns on a channel to start heating the iron. In other words, when Q2 or Q8 get turned on. I have traced the spikes to connector IRON J2.
On the other hand, the spikes are lost / filtered out in the controller power supply path. The second image of the scope shows that there are no spikes on VPre line but voltage drops are still present. I suspect this is normal. It rises the question "Why does the controller loose power and restart?" though. The voltage drop on Q1 Uce = -1.63V.
I have also measured the voltages on the PWR J3 connector. They have very little noise, unmeasurable with my scope. Front board not connected:
DVdd = 3.295V
3.3V = 3.292V
-0.6V = -0.5309V
Front board connected:
DVdd = 3.295V
3.3V = 3.186V
-0.6V = -0.6850V
Should 3.3V rail draw so much current that SMPS couldn't regulate the voltage? Why the hell is -0.6V rail more negative than unloaded?
Hello guys, almost done with my unisolder. It is functional and heats the tip. My problem is that there are huge voltage drops on the power rail. Because of that it only works on my lab bench PSU, where I can set the voltage. Above cca 16V the drops become so large that the controller power cycles. Consequently, on AC the controller doesn't at all since I only have 24V transformer... which has even higher DC peaks. I have measured the voltage rail with oscilloscope. The channel was AC coupled an I could see the peaks getting bigger with increasing voltage. I read in this forum thread, that user @RRRoamer was having voltage drop problems. His issue was wrong zener diodes in valley-fill circuit. My components measure fine. I have even replaced Q5 just to try. I've also removed D12 and R9, to completely eliminate this part of the board. I don't know what else to try. Can anyone point me in a direction? What else could I measure?
