Hakko fx-888d themister(?) - Page 1
Forum section: electronics / repair

author: NightSilence
author_rank: Newbie
timestamp: September 01, 2024, 06:46:51 pm
content: Hey,I am trying to figure out why m hakko fx-888d stopped working. I did continuity check and realized that the themister(?) is busted. There is no continuity between one leg of it to the other. Can someone point me what kind of themister is this, if it is themister? And can this be replaced?

author: floobydust
author_rank: Super Contributor
timestamp: September 01, 2024, 07:05:17 pm
content: That is a varistor for mains surge protection. It should have no continuity, and note it goes across incoming power.Something else is wrong with the FX-888D. Check ACV on the transformer secondary pins. Or measure Ohms across the end of the power cord (not plugged in obviously).

author: NightSilence
author_rank: Newbie
timestamp: September 01, 2024, 07:27:22 pm
content: I tested that two pins in the pic are getting 120v. What else do I need to test?

author: NightSilence
author_rank: Newbie
timestamp: September 01, 2024, 07:48:44 pm
content: I should have mentioned this earlier, I am currently using wire to make connection, because the fuse was busted. It's temporary solution.It was working fine. I used it whole day yesterday. Today when I turned on the device, I heard something tripped. When opened, I noticed that the wire was touching this pin. And it hasn't turned on since then.

author: floobydust
author_rank: Super Contributor
timestamp: September 01, 2024, 07:49:12 pm
content: Measure the output of the transformer, the pins are on the other side of the bobbin. It should be roughly 24VAC.Or like I said earlier, measure resistance at the power cord prongs. With anything dead, the first check is the fuses.DUDEduct tape and flying loose wire is a quick way to destroy anything, yourself included.For that reason, I'm out.

author: J-R
author_rank: Super Contributor
timestamp: September 02, 2024, 10:43:38 pm
content: Yes, it doesn't seem like you have quite enough experience to be doing this!However, the first order of business is to replace the fuse and restore proper protection. If you would have done the repair correctly the first time, you wouldn't be in this situation now! And don't use the Hakko to solder on itself, if that wasn't already obvious.But beyond that, I think the next area to look at would be the primary side of the transformer, specifically the connection that you pointed out was shorted to that temporary wire. You may need to remove the transformer completely if there are PCB traces on the other side that need to be inspected, or to get a better view of the transformer. Then continuity test the transformer windings looking for an open. If you're lucky, maybe a wire coming off the transformer windings going to the connection pin will be melted open and you could repair that. Most likely you will need a new transformer, though, since rewinding a transformer is expert level.

author: coppercone2
author_rank: Super Contributor
timestamp: September 02, 2024, 10:45:08 pm
content: hahaha at that wire it reassured me that someone will find a wayDon't have strands like that, they will fall off and cause a short circuit and possibly electrical explosion or hang off the PCB energized to mains and shock your arm when it gets too close