Is my rework station a death trap? - Page 1
Forum section: electronics / beginners

author: AllanJ
author_rank: Newbie
timestamp: July 23, 2014, 02:04:30 am
content: Hi guys. My 1st post here, be gentle with meA few months ago I bought a Chinese 852D+ rework station for carrying out smartphone board repairs. I'd heard stuff about poor build quality on things like this so first thing I did was open it up and check to see if it was fused and earthed. All looked ok to my somewhat untrained eye, with proper fuse (albeit in the neutral line only), the case had a clean earth connection and everything looked neat and tidy. Switched it on and everything seemed to work as it should so I put it to use straight away. So far so good ...A little while ago the soldering iron blew and I bought a replacement element. After fitting it I checked to see if the tip was earthed - something that I'd not thought to check before - after all it says "ESD Safe" on the front of the controller so it must be earthed, right? Er, no. The iron itself is ok - it has a 5 pin connector and pin 3 connects to the tip. But pin 3 on the controller does not go to ground. With the iron connected I measured ac voltage across the tip and the grounded case - I get 26.8 volts! That's with the unit connected to mains with nothing actually switched on - the tip voltage does not change when the iron is switched on.I had a look inside again. Turns out the only thing that's earthed is the case, and the PCB and everything else is isolated from it. One of the ICs on the PCB has a pin marked 'gnd'- I toyed with the idea of simply running a wire from that pin to the earth tag on the case - but I don't know enough about these things to judge if that would be a wise move? A schematic would help but I've been unable to find one, for this or any other 852D+ station. There is no hint on the outside of the device nor on the accompanying esoteric 'manual' as to who the manufacturer is - but the PCB is evidently made by YouDe, a company I suspect is responsible for producing many of the clones out there.An obvious course of action would be to junk the thing and spend more money (a lot more money) on a more respectable unit - but surely it can't be too difficult for someone who knows what they're doing to modify this one so it works properly? I'm competent with a soldering iron but I don't have a clue about circuitry - can anyone give me some simple guidance? (Like am I risking anything by connecting that 'gnd' pin to the earth tag ... )I should mention that I've used this device, soldering iron and hot air blower (also recently discovered has >10VAC at the shroud) to replace damaged or missing SMD / BGA components on iPhone 4 and 4S logic boards and restored them to full working order - I've done six to date. And surprisingly I haven't actually destroyed a board yet (I'd find this surprising even if my rework station had been behaving normally!) So maybe I should pretend I haven't noticed anything out of the ordinary and carry on regardless!

author: sleemanj
author_rank: Super Contributor
timestamp: July 23, 2014, 06:03:57 am
content: You might want to read and post in this thread:https://www.eevblog.com/forum/reviews/w-e-p-yihua-852d-combined-hot-air-station-and-soldering-iron/Take some photos in case your version is different.Iron tip should be connected to earth ground a for safety and mainly for ESD - this is really only meaningful if you are working on an ESD work surface connected to the same earth potential, if you're not.More importantly is that the blower shroud should be earthed for safety - there is likely full mains voltage running through the element under that shroud, unlike the iron element which is much less than mains.The PCB should have a ground point to earth ground, usually this would be via a mounting screw into the earth'd chassis, but if it's mounting into plastic, obviously there would need to be a flying wire. Have a look to see if there is an obvious omission, you know what common PCB earth ground mounting points look like, mounting hole with large exposed annual ring obviously connected to ground.

author: AllanJ
author_rank: Newbie
timestamp: July 23, 2014, 11:36:46 am
content: Quote from: sleemanj on July 23, 2014, 06:03:57 amThanks for this. I did consider posting on that thread you quoted but as the discussion effectively ended 3 years ago, with one post added fairly recently but ignored, I thought I'd better start a new oneI was expecting to find an earth connection for the PCB present but ineffective, like dry joint or onto painted metal, but there is no earth connection of any kind that I can see. There is one earth terminal brazed to the case and solely the earth lead from the incoming mains cable connected to it. The PCB is mounted solely by the three temperature/air-flow control pots on the face plate, the casings for which seem to be isolated. I can see nothing on the PCB to suggest an unused earth terminal; as I said the only hint of earthiness I can find is the IC pin marked "gnd" - I did a random scout around some of the caps with a continuity tester and noted that several of them had one leg going to this 'gnd', circumstantially suggesting it is indeed a ground point. It does seem fairly obvious that running a wire from 'gnd' to the earth terminal would do the trick - but, as I said before, I'm basically ignorant about these things and I just want to be sure that this isn't an example of some kind of alternative arrangement where the PCB, solder tip etc are left unearthed, all in the interests of "ESD safe" ness, and attempting to earth it won't result in terminal disaster!!! I'm intrigued to know why repeatedly applying solder to iPhone logic boards and components with nearly 30VAC at the iron tip hasn't wreaked untold havoc!I'll post up some pics if it helps - I don't know if it's different from the unit/s discussed in the other thread because I can't see any photos on it.PS I do work on an ESD work surface connected to the same earth. And when I've got the general earthing question answered I'll certainly ground the blower shroud as you suggest

author: amyk
author_rank: Super Contributor
timestamp: July 23, 2014, 12:11:48 pm
content: Quote from: AllanJ on July 23, 2014, 11:36:46 am- Protection diodes- The circuit must be complete for current to flow (and cause damage)

author: AllanJ
author_rank: Newbie
timestamp: July 23, 2014, 12:32:19 pm
content: Quote from: amyk on July 23, 2014, 12:11:48 pmThat's the sort of answer I'd been kinda expecting. So does this mean the unit is designed to be run without anything earthed apart from the case? If so, is this really a good idea?

author: zapta
author_rank: Super Contributor
timestamp: July 23, 2014, 02:53:14 pm
content: Quote from: AllanJ on July 23, 2014, 12:32:19 pm26V between the tip and ground is not a good idea.In the past I got one of those small Chinese digital hot air stations and returned it after inspecting the internal ground path.

author: Rick Law
author_rank: Super Contributor
timestamp: July 23, 2014, 04:42:05 pm
content: Quote from: AllanJ on July 23, 2014, 02:04:30 amIt could be merely induced voltage... You will get interference even over a foot away from a typical wall-wart. All AC will emit EM field at very low energy. My 3COM managed switch (old now, but $2000+ when new) well build and well shielded could still be read as an AC volt meter at 1/2 meter away.To test if it is a short or an induced voltage, put a small load on to it, say a 100K resistor, the voltage disappear if it is induced.

author: AllanJ
author_rank: Newbie
timestamp: July 23, 2014, 10:16:08 pm
content: Quote from: Rick Law on July 23, 2014, 04:42:05 pmHmmm. I'd like to try that but unfortunately I don't have a stock of resistors. Trying to think what else I might have to hand that may have that kind of resistance.

author: AllanJ
author_rank: Newbie
timestamp: July 26, 2014, 12:17:18 pm
content: OK, I acquired a 100k resistor ...Today I measured 56v ac at the soldering iron tip (yesterday it was 28v. WTF etc). Voltage dropped to zero when I applied the 100k loadSo, from the results of this experiment, together with other information on this thread taken into consideration it appears that:1. My workstation may not be a death trap2. My workstation (YouDe 852D+) is designed to be run with an unearthed soldering iron.3. That I have used this soldering iron to desolder/solder many components (including cleaning and hand re-balling a 63 pin BGA IC) on several smartphone logic boards without any kind of mishap suggests that this unearthed soldering iron arrangement works just fine, and ...4. It's probably ok to continue using it without modification.Maybe I'll post this somewhere else on the forum, see if it upsets anyone!

author: Rick Law
author_rank: Super Contributor
timestamp: July 27, 2014, 01:00:52 am
content: Quote from: AllanJ on July 26, 2014, 12:17:18 pmSince I was the one suggesting apply a 100K load, I suppose I should say something...Yeah, if a 100K resistor makes the 56V disappear, it looks like induced voltage. (Rounding to 50V for quick math):At 100K load, a 100V source should give it 1mA, a 50V source 100K load should give it 0.5mA. 50V@0.5milliAmp = 25milliwatt. If your 50V source source can supply 25milliwatt, it would have held the voltage at 50V.You have shown the source obviously cannot supply the 1/2mA (50V got pull down to 0 volt). Therefore, your "source" must be below 25milliwatt power (or it would have been able to maintain 50volt.)I suspect current going around the heat coil use the power wire and the heat coil winding like a transformer inducing the voltage at tip-to-ground you measured using your meter. This induced voltage is below 25mW power. Exactly what induced power it got (can deliver) is hard to say, we know that it is below 25mW, and it is certain no danger to human life.Disclaimer, I am not an EE expert... I am a Physics guy.Rick

author: onlooker
author_rank: Frequent Contributor
timestamp: July 27, 2014, 01:58:53 am
content: If the leakage is a concern, be it by induction , or capacitance, or resistance, you may want to check the leak current or insolation resistance.For mains powered equipments, these are either in the specification or implied by some (local) standards. If you have doubt, you need to check it on your own.For example, my isolation transformer modified from a medical grade isolation power conditioner was speced as having leakage current < 50uA and the real measurement showed 30uA. This is an easier check than the insolation resistance for a hobbyist.

author: zapta
author_rank: Super Contributor
timestamp: July 27, 2014, 02:08:15 am
content: Soldering electronic components with a tip that has 56V RMS open circuit does not sound as a good idea.

author: Rick Law
author_rank: Super Contributor
timestamp: July 27, 2014, 05:09:18 am
content: Quote from: zapta on July 27, 2014, 02:08:15 amI would have to agree with that. But picking up some induced current is normal. EM noise is everywhere. 56V is rather on the high side. At least it is not a "death trap" if it is not providing any power. A mere 100K load will pull it to 0V as reported.This is my book would be "I don't like it, but it isn't going to be deadly."

author: sleemanj
author_rank: Super Contributor
timestamp: July 27, 2014, 07:33:32 am
content: What it says to me though, is that the tip is not grounded in any way, and therefore any static charge on the tip is a danger to any sensitive devices.If it was me, and I was working on sensitive devices, and I was working on an ESD mat, with an ESD strap, and observing at least some ESD practices... leaving the tip ungrounded seems like a big old fail to me.The middle pin of the Iron's DIN socket is the tip (confirm with a multimeter), it should be either grounded (via resistor), or connected to an ESD bonding point.If it was me, I'd take a 1M resistor, and connect it between that pin and the case permanently to ground out the tip.

author: Bukurat
author_rank: Regular Contributor
timestamp: July 27, 2014, 12:15:48 pm
content: I recently purchased an 853D combined hot air and soldering station and DC power supply from an eBay seller located in OZ.Fuse in active side. CheckCase earthed. CheckSoldering iron tip earthed. CheckHot air blower shroud earthed. CheckLooking good. The power cable had ANE marked on the correct pins on both 3 pin plug and IEC socket.For some reason I thought to check the cable wiring, wouldn't know it, despite the clear markings the manufacturer managed to reverse active and neutral in the cable.

author: zapta
author_rank: Super Contributor
timestamp: July 27, 2014, 03:51:37 pm
content: Quote from: Bukurat on July 27, 2014, 12:15:48 pmThe quality of the ground path also matters. The thickness of the wires, the quality of the contacts, etc. You want a reliable ground path that will last for the lifetime of the unit. This is something that it's hard to verify from the outside.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: July 27, 2014, 04:03:51 pm
content: well, i was electrocuted once with one of this crap chinese thing, i was surprised when am doing some soldering on a board when iron tip touch the circuit some led in the board light up

author: Rick Law
author_rank: Super Contributor
timestamp: July 27, 2014, 04:52:42 pm
content: Quote from: sleemanj on July 27, 2014, 07:33:32 amDitto...Kill two birds with one stone, kills induced voltage and static discharge...1M resistor is the best deal. For 1 cent, you get a million ohm. Where else can you buy a million something for a cent..

author: zapta
author_rank: Super Contributor
timestamp: July 27, 2014, 04:59:22 pm
content: Quote from: Rick Law on July 27, 2014, 04:52:42 pmGood point. I am going to buy three ;-)

author: AllanJ
author_rank: Newbie
timestamp: July 28, 2014, 01:51:12 am
content: Thanks for your continuing advice, good people.This has all been very educational. I guess what I was expecting when I posted this thread were comments like "dangerous rubbish built on the cheap - this that and the other has clearly been assembled wrongly, corners have been cut etc, you need to do such and such things to rectify it". But I've been getting the impression that perhaps this device isn't that bad after all. As I said, the build quality seems pretty good, it all looks neat inside - but I'm unable to judge the quality of the circuit design and the suitability of the components. I'm told I can work with an unearthed soldering iron tip because of "protection diodes" - so perhaps this device isn't earthed by design?Anyway, I've been convinced that grounding the soldering iron tip is what I should do. So that's what I've done. Pin 3 of the soldering iron din connector, which connects to the tip, now goes via a 1m? resistor to the earth tag on the case. Tip voltage is now 3.12VAC. I was expecting something closer to ambient, around 30mV perhaps, but it's certainly a whole lot better than 56v!Which brings me to the mains cabling etc. The plug is correctly wired but the fuse is in the neutral side. Line/active and neutral both connect to red wires - I had a quick look at the board and among the destinations for these red wires the neutral one goes direct to one side of the heating element in the blower and the active one goes to the other side of the heating element via a triac. So should I just rewire it so the fuse is in the line/active side?

author: Rick Law
author_rank: Super Contributor
timestamp: July 28, 2014, 02:55:07 am
content: Quote from: AllanJ on July 28, 2014, 01:51:12 amI think to some extend and in some cases that is true. I see China like the "wild west", plenty of good, plenty of bad, and changing rapidly. There is always good people even in a bad town unless Clint Eastwood was recently in town and eliminated the bad and the ugly.I think more of them are okay or even good design but just plain badly build. I think it is a mindset thing. Once they get a good design (that must be done by an educated person), the part that a trained monkey could do, trained monkey if cheaper would be hired. So, unless quality level is part of the contract/deal, otherwise, the bar is "as long as it works".I look at those as an opportunity to leverage my own skill - apply my skill to repair/improve it and end up with something decent at lost cost.Quote from: AllanJ on July 28, 2014, 01:51:12 amHow about doing another check to make sure that you have no shorts at all to put your own mind at ease. 3.12volt with the 1M resistor is just 9.7 microWatt, not a lot. Also, you know that a 100K resister will take it to zero volt, after a final check, you could hook in a 200K or a 100K. (My YiHUA soldering iron is direct-grounded at about 0.6 ohm between the tip and earth ground. My other good but very old iron is direct grounded too. $70 in late 1970, so that one is no cheapie.)

author: SeanB
author_rank: Super Contributor
timestamp: July 28, 2014, 04:44:34 am
content: Change the fuse so it is in the live, though you are in the UK with fused plugs, so change the plug fuse as well to a 3A one which will offer added protection.

author: AllanJ
author_rank: Newbie
timestamp: July 31, 2014, 04:04:09 pm
content: Quote from: Rick Law on July 28, 2014, 02:55:07 amQuote from: zapta on July 27, 2014, 03:51:37 pmCarried out some checks and discovered the earth points in the room are not entirely consistent. Rearranged things so that resistance from the ground pin at the workbench to the bonded earth-point to the building is 0.1 OHM, best I can manage. Means I now have 21mVAC at the soldering iron tip, which is far healthier.Also voltage at the blower shroud is down to about 30mVAC (from 10VAC) which I'm happier with - but it isn't grounded. Achieving this isn't something I feel equal to at the moment! Not sure how I'm going to connect a wire to the shroud, then there's the matter of routing the wire inside the air tube which will entail breaking and remaking the air seal into the case. I'm always very careful not to touch the metal part of the blower onto anything when it's on so I reckon I'm safe enough.Quote from: SeanB on July 28, 2014, 04:44:34 amI have a 3A fuse in the plug, which is of course in the live, so was thinking perhaps it wouldn't hurt to leave the (6A) case fuse where it is in the neutral?Anyway I now feel much more confident about my rework station thanks to you guys, I'm glad I came here