Soldering station T12-953 fuse blown - how to fix?

[nb]

Hi All,

I am a hobbyist using a Quecoo T12-953. It was working well for years, until the fuse (250V 3A) was blown when I was working with an old TV pcb.

Perhaps I was not so careful enough. After resoldering a few spots, when the tip touched another spot to resolder, the fuse was blown. All but the fuse insider the soldering station looked okay, so I replaced the fuse, but when I turn the station again, the fuse was blown again. I removed the soldering handle cable from the station and tried again, but again the fuse was instantly blown.

What would have gone bad in the soldering station? When I measured the resistance between AC input, no shortage was shown. How could I fix it?

Comments will be appreciated very much!

[nb]

It turned out that two of the rectifier diodes were bad (closed). They were M7 (smd version of 1N4007) but the only parts I had was 1N4004. Their difference is the max reverse voltage (700V vs 280V). Because 280V is still higher than the mains voltage, I thought 1N4004 would also be okay. I replaced the bad M1 diodes with 1N4004, and the soldering station worked well. So, luckily, other parts were not damaged, I guess.

Perhaps I should be a bit concerned about using 1N4004? After this weekend I may have to order some M7 or 1N4007...

[Doctorandus_P]

Do you realize that 230Vac RMS is a bit over 300V peak?
And here in the EU, that is nominal voltage, and mains can be upto almost 250Vrms = 350V peak.

And that is without surges, lightning strikes and other nasty business, so indeed putting in diodes for a higher rated voltage is advisable.

[wraper]

Do you realize that 230Vac RMS is a bit over 300V peak?
And here in the EU, that is nominal voltage, and mains can be upto almost 250Vrms = 350V peak.

And that is without surges, lightning strikes and other nasty business, so indeed putting in diodes for a higher rated voltage is advisable.

1n4004 has 400V peak rating and 280V RMS. Still it's uncomfortably close and does not account voltage surges.

[nb]

Thanks a lot for your comments, Doctorandus_P and wraper! It was exactly what I needed. As suggested, I will replace them with 1N4007 or M7.

By the way, what is a "standard method" to make an appropriate choice of peak rating (eg accounting voltage surge) in such a situation? I'd like to learn more, because my hobbyist knowledge was limited to only comparing mains' 220V RMS and diode's 280V RMS...