Hi anyone using weller WE1010 soldering station?
I have this unit (my mains is 220VAC 50Hz so I use it with a 220v-110v step down converter) and suddenly it stopped working.
So I opened it up and did the following tests:
1. transformer primary side shows 8 Ohm, secondary side shows 0.5 Ohm resistance
2. Secondary Polyswitch and Fuse was good.
3. At power applied, primary side has 100VAC 50Hz, secondary side shows 19VAC rms
4. The onboard fuse on the PCB was also fine.
5. But the 470 marked resistor ( R22, is it a 3 watt one?) on the attached picture shows a variable value roughly from 250 KOhm - 1M Ohm.
6. The rectifier diodes(D4, D3) were good and forward voltage was 0.6V tested with my DMM.
7. But the rectified DC voltage across the electrolytic cap showing around 2-3V, so obviously the 7805 voltage regulator was not supplying any DC current to the main controller.
I have tried to reconstruct the rectifier circuit from the PCB traces.
Please see the schematic picture I have added.
I don't recognize either of the diode markings (729 ZHK and A4) , nor I found anything useful by searching them on google. there ar lot of diodes with similar markings.
Also the diode rectifier part is a bit odd to me. Is it possible that D4 is a zener dropper in combination with R22 and the D3 is only acting as half rectifier?
In that case R22 is damaged by an overcurrent (may be an unusual in rush or surge) condition makes sense to me ( just suspecting, I am not an expert on electronics).
Also I don't understand why didn't the fuse tripped first in that case.
So after all these tests my guess is the 470 marked resistor is somehow gone bad.
But I am still confused to replace it with a good 47 Ohm with it because I m not certain about the root cause that made the resistor to fail.
Any ideas anyone?