1

My soldering iron was working fine for a few years. One day, I used it and it worked fine again, then I unplugged it then tried to use it again a couple of hours later but it wouldn't heat up.

I took it apart and pulled a Big Clive and mapped out the schematics. I tested the few components and they seem fine. Both of the SMD resistors check out as does the SMD capacitor. The diode doesn't register with the diode-tester on my DMM, but my Mega328 ESR/LCR tester detected it as a diode. I don't know what resistance the pot should have, but it definitely seems to have a range (it's not shorted or open).

The 97A6 thyristor/triac seemed dead (I don't recall the exact nature of the failure), so I got a pack of MAC97A8s, tested one, and put it in. I don't think the orientation of the triac should matter, the gate is in the center either way and iirc, the anodes are both functionally equivalent.

The only thing left that could have a problem is the ceramic heating element, but I have no idea how to test that (I don't know what properties, such as resistance, it's supposed to have).

Is there some way to diagnose the problem?

I already got a replacement, but I'd like to salvage this iron and avoid throwing it out if possible. (My old one with the wire-wound element died the same day this one died, so I'd like to keep this as a backup until I can get another backup backup, and also just not waste what seems like a perfectly usable iron—well, other than the not working. )

Front (with new triac): Dead Soldering Iron Front Back (with wires splayed to show traces—yes, I know I didn't trim the leads yet): Dead Soldering Iron Back Original triac: enter image description here

Synetech
  • 363
  • 2
  • 4
  • 12
  • 1
    Triacs are *not* symmetrical. MT1 \$\ne\$ MT2 – Spehro Pefhany Sep 28 '21 at 02:13
  • Doh. Well I checked the photo I took of the original before putting the replacement in, and it was flat-face-down. I checked the datasheets for the original and the replacement and they both had the same pinouts, so it (should be) correct. (I also tried putting a triac in the other way around as a test, but that didn't work either.) – Synetech Sep 28 '21 at 02:56
  • The soldering on pretty much all components is poor. D1 in particular looks very fishy. I would strongly advise to redo every single joint, use flux. Very ironic that the companies making solder irons don't know how to do proper soldering... – Lundin Sep 28 '21 at 07:42
  • You can usually find an inexpensive heating element on Bang Good or where else these soldering irons are sold. Try Amazon too. – MicroservicesOnDDD Jul 08 '22 at 14:55

1 Answers1

2

Element is often a prime contender.
Resistance when hot is about
R = V _squared/Power_max.
R is usually reasonably temperature independent.

R MAY be lower if they never run at 100 % duty cycle.

Place a resistor of somewhat above R_calculated across element, set on low heat and see if it gets warm.

Russell McMahon
  • 147,325
  • 18
  • 210
  • 386