DC voltage on T12 soldering tip - Page 1
Forum section: electronics / general

author: p_wats
author_rank: Contributor
timestamp: October 12, 2022, 01:15:12 am
content: Long story short, I'm measuring 1-3v DC on the tip of my Shinenow T12 soldering station.The soldering tip itself is grounded via a wire directly to the IEC ground (this was present upon arrival, but I also added a chassis ground, which was absent). However, it appears the PSU and controller section don't share the same ground (there is no continuity between them), so some DC voltage seems to still be reaching the tip.Is it as simple as connecting the controller section ground to the same chassis ground as the rest, so everything is grounded to the same point? I tested that with a gator clip and it removes the DC from the tip, while everything else seems to work as normalI'm trying to decide if I relegate this station to non-sensitive components only (had a few too many chips mysteriously fry since getting this unit) and buy a new, more reliable station for CMOS, MOSFETs, etc. or if making sure both the AC and DC portions of this circuit are connected to ground would be enough.Here's a pic (before I added the chassis ground). The green and yellow wire is the ground for the tip.

author: ygi
author_rank: Regular Contributor
timestamp: October 12, 2022, 08:56:46 am
content: Both encoder and iron plug body are metal and make direct contact with the case which should be grounded/earthed. They are also internally connected to the controller board gnd plane. That in itself should tell you they are meant to be tied together but aren't because of cheap/lazy assembly.

author: p_wats
author_rank: Contributor
timestamp: October 12, 2022, 01:13:46 pm
content: Quote from: ygi on October 12, 2022, 08:56:46 amGood point. I had already grounded the power supply board/IEC connector to the chassis, but seems that only took care of the AC power supply circuit, with the DC ground still floating.Easy enough to connect the DC ground to the chassis too, I suppose. Just wanted to double check before going ahead. The unit works well on non-sensitive stuff, but I'd sure love to not fry any more FV-1 chips (could always just use my ancient Weller on those).

author: ygi
author_rank: Regular Contributor
timestamp: October 12, 2022, 08:20:04 pm
content: That's what I'd do too.

author: p_wats
author_rank: Contributor
timestamp: October 14, 2022, 03:06:11 pm
content: Thanks for the help!

author: thm_w
author_rank: Super Contributor
timestamp: October 14, 2022, 09:35:55 pm
content: Earth grounding the tip is the important part here, doesn't matter if the DC is floating.If you want to do it because you don't trust the manufacturer for your own safety, ok.Use a multimeter to check resistance from iron tip to ground on the end of the power cable you are using. Then use an outlet tester to verify that the wall outlet is properly earthed.

author: p_wats
author_rank: Contributor
timestamp: October 17, 2022, 02:30:22 pm
content: Quote from: thm_w on October 14, 2022, 09:35:55 pmThe tip is earth grounded. It's the floating DC that worries me, as I'm able to measure a fluctuating amount of DC voltage on the tip, which I assume is a bad thing when it comes to sensitive chips, etc. After receiving this unit I had several projects not work due to fried chips (something that never happened with my beat up old Weller), so I just haven't been working on anything other than simple patch cables for a while.

author: thm_w
author_rank: Super Contributor
timestamp: October 17, 2022, 09:15:58 pm
content: Quote from: p_wats on October 17, 2022, 02:30:22 pmMeasure from where to the tip?You shouldn't measure any significant DC unless your earth ground path is bad. Shut the station off and measure the resistance to the plug, and that the outlet is good, as I noted.

author: p_wats
author_rank: Contributor
timestamp: October 17, 2022, 10:07:08 pm
content: Quote from: thm_w on October 17, 2022, 09:15:58 pmI've measured continuity between the tip and ground lug of the IEC cable (there is a cable wiring the tip directly to power cable ground).As for DC, using my DMM with one test lead on the DC ground and another on the soldering tip I can measure a fluctuating amount of DC voltage that increases depending if the station is heating up or stable.The DC portion of the circuit is not grounded to the same point as the power supply circuit (no continuity between grounds on the different boards).

author: thm_w
author_rank: Super Contributor
timestamp: October 17, 2022, 11:13:39 pm
content: Measuring voltage from DC ground to the tip doesn't really mean anything, as the DC section is floating.No ICs will be harmed as long as your earth ground is connected to your static safe mat + wrist strap, which is also connected to the tip.

author: p_wats
author_rank: Contributor
timestamp: October 17, 2022, 11:31:13 pm
content: Quote from: thm_w on October 17, 2022, 11:13:39 pmHmm. I guess that makes sense, as it's not like the circuit I'm working on would share a ground connection with the T12 control board. I don't currently have a mat or wrist strap (most of the stuff I deal with isn't very sensitive, until a few recent digital chips), but could get those.Basically, I figured I'd try a T12 unit to replace my old entry level Weller (no temp control, etc.) and since switching I've had problems with several of the same FV-1 chips and a few transistors in a row, when I never had any issues prior to using this unit, so I was hoping the measured voltage would explain that, but sounds like that's not it?

author: thm_w
author_rank: Super Contributor
timestamp: October 18, 2022, 12:54:50 am
content: If your body is statically charged, and you are say holding the IC in one hand, and then touch it with the iron in the other hand, the grounded tip could almost be worse as its a lower resistance path to ground. Not sure if that is a realistic scenario though. Either way, ESD mat is a good idea if you deal with any sensitive ICs.I suspect you'd be feeling and seeing the static shocks at the point that this stuff is being damaged though.. as it should be reasonably robust.I assume you have the iron set to a reasonable temperature?There is not chance its a bad connection or something right, you swapped out the transistors and then they worked? Did you measure the transistor out of circuit and see it shorted.

author: p_wats
author_rank: Contributor
timestamp: October 18, 2022, 04:39:22 am
content: Quote from: thm_w on October 18, 2022, 12:54:50 amYeah, no abnormal temp or anything. I've used the same station on a few simple things without issue.It just so happens that after I got this station I burned through 4 FV-1 chips in a row (purchased from different, reputable sources) in circuits I had previously built without issue. After extensive troubleshooting in the forum dedicated to the circuit in question, the only remaining theory was that these usually somewhat robust chips were being fried somehow, even though everything else in the circuit measured correctly (I had also restarted with completely new boards/parts a few times, to be sure). This soldering station seemed to be the only remaining variable.I basically took a break from soldering after that, as it was too frustrating. I've since moved and am setting up a new work space as I want to build a few things, but am apprehensive, having never solved the problem. It's possible the station has nothing to do with it, but it's the only thing I can think of at this point.