Yihua 959D hot air station - cautionary note - Page 1
Forum section: electronics / general

author: mcovington
author_rank: Regular Contributor
timestamp: November 17, 2022, 03:14:12 am
content: I just bought a Yihua 959D hot-air station from Amazon for occasional use. Having been warned about such things in other Chinese equipment, I opened it up and found that the fuse and power switch are in the neutral wire, not the live wire. (They may have been misled by the US color code, black for live, white for neutral; I believe the old British code is black for neutral, red for live; now blue for neutral, brown for live.) (If I've mixed any of this up, tell me!)I'm going to swap the live and neutral wires coming into the unit; maybe even fit a power cord with the newer brown-blue-green color code. I'd rather have peace of mind about that than have a valid warranty...The other thing I wanted to verify is that the power switch does cut off all incoming AC power, and it does. Not just the control circuitry. If the latter had been the case, a shorted triac might leave the heating element energized with the switch off.

author: Shock
author_rank: Super Contributor
timestamp: November 17, 2022, 04:32:49 am
content: Do check when it's unplugged that the pin to wire is correct (effectively wrong pins and wrong color code) as well as earth.You are right you shouldn't leave cheap chinese stuff powered on at the wall. I'll go as far as swapping nasty low cost smps out.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: November 17, 2022, 04:53:32 am
content: I just use a cheap Atten hot air gun and it has been very good.Only mishap was me leaning down to pick up blower without looking properly and grabbed the hot end !It burnt me quite badly but I guess it would at 400 degree's.

author: mcovington
author_rank: Regular Contributor
timestamp: November 17, 2022, 02:02:34 pm
content: Yes -- I looked inside and will look inside again -- because of course there was the possibility that the colors were just backward throughout. No; it really is the live wire that they've switched and fused. But I will trace everything before modifying. A lot of unrelated wires are tied together with a zip-tie. I want to divide this into 2 bundles, high and low voltage.If I arrange it so that the on-off switch completely cuts the live wire, and there is no other connection from the live wire to anything inside, do you think it is safe to leave it plugged in, or should I still unplug it (or turn off an upstream power strip) when not using it?

author: Shock
author_rank: Super Contributor
timestamp: November 17, 2022, 03:33:10 pm
content: If a power switch and fuse isolates the mains, it will be as good as those two components. I typically leave equipment that switches power off fully plugged in, and most of my gear is not chinese. In my opinion a smoke alarm is a must.My test equipment run off a server pdu which avoids me reaching behind things. It's a trade off using the computer to turn things on but I can stagger powering gear on automatically, in groups or off. One switch turns off all my test gear is quite useful, handy to have separate dut and lighting circuits as well.

author: mcovington
author_rank: Regular Contributor
timestamp: November 17, 2022, 05:21:12 pm
content: I've decided to put all my soldering equipment on a switchable power strip that will also contain a fairly prominent red light (not just its indicator, but an actual small light of some kind) so I'll be well aware if it's on or off. That way there will be two switches between me and disaster. And yes, we have smoke alarms.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: November 17, 2022, 05:26:21 pm
content: Which version do you have? My hot air station is the 'black panel with blue buttons' version which seems to be an 'evolution' from those described elsewhere. But the hot air handle/jet engine is the same piece of plastic ***p.I did the safety cable check (thanks Dave) and, live is correctly tagged to the fuse. Live-nuetral polarity is maintained on the PCB. Earth is tagged to the transformer. Earthing the rest of the case relies on the 'cut' of the bolts on the (painted) baseplate. A problem for the China assembly slave tasked with making 100s of these a day, might be the live and neutral wires are joined to identical colored red wires?With my Yihua 959D, I thought of replacing the mains side with a combined 3 pin socket, fuse and switch, mounted on the back. The sub-minature switch on the front would then be a neon indicator. In the end, I just replaced the front switch with a neon version as this is not a 'bench' installation. [ See attached image ] btw The pot went nasty very quickly, so was replaced. I also tidied those cable looms!I attempted a schematic of my hot air station too, which I will post here soonwhenI get hold of the Kicad files.

author: mcovington
author_rank: Regular Contributor
timestamp: November 17, 2022, 05:41:28 pm
content: I have the very latest (black, blue buttons) as shown in this Amazon link -- have only had it a couple of days -- and have put the wand rest on the left rather than on the right. I'm going to open it up again and double-check wiring and make sure live goes to the switch and fuse. I may put in a longer power cord at the time.https://smile.amazon.com/dp/B08BK3M6YW?psc=1&ref=ppx_yo2ov_dt_b_product_detailsI'd really like to see that schematic!

author: AndyBeez
author_rank: Frequent Contributor
timestamp: November 17, 2022, 06:32:40 pm
content: I'm a 'lefty' too! I think there is a factory temperature calibration mode, but I have found nothing anywhere online. Anyone else know of this? I placed a thermocouple in thejet wash(right term?) and, +/-10C, was accurate enough for my shrinking and melting tasks.Important: With my British/European/240V version, the heater operates at mains potential. Hence the metal casing of the heatermustbe connected to earth. Check you have continuity between the metal case and the earth pin on the power plug.For those interested, here is the hot air handle exposed. You'll note the location of the reed switch, which the uC 'senses' in the holder. The fan is a 24V axial blower. Note the quality volume hand solderingI wonder if there should be a 180C rated thermal fuse in there? Although the fan seems to have a 'fan speed' pin, the intake can still block - or worse the triac can fail 'on'. So the temperature behind the handle might raise enough to melt the plastic before the operator drops it! Thoughts anyone?+++ EDIT +++ I Just noticed how close the bare metal casing of the heater is to the bare metal lead of the reed switch. About a 3mm gap. I think there is some high temp sleeving missing. Or not. Also, the wiring PCB and cables are obstructions in the airflow.

author: floobydust
author_rank: Super Contributor
timestamp: November 17, 2022, 07:38:41 pm
content: These chinese hot air stations are unsafe. There's youtube videos, fire when the triac shorts, the connector having hazardous live present (even when switched off), no or crappy PE ground to the heater tube, the wand cable and pc board not rated for mains voltages and the current, the main pc board having indequate spacings, fuse is way too big, etc. etc.I havetwothree rules:1. Never ever leave it plugged in to mains.2. Feed it power through a GFCI.3. Never leave it unattended, even in cool down.The low price has some caveats and then add in low quality components and no safety approvals, it's a bit too unsafe out of the box.

author: mcovington
author_rank: Regular Contributor
timestamp: November 17, 2022, 07:50:42 pm
content: Two, for sufficiently high values of "two"Seriously, I hear you. I am going to give mine a thorough looking over (internally); I think it lacks most of the safety hazards reported in earlier ones, especially after I fix the swapped live and neutral on the power cord, and verify that the power switch actually cuts the live wire and there is no other path for 120V AC into it. I am also going to keep it either unplugged or plugged into a turned-off power strip. I've just set up the power strip, which has a small but conspicuous light on it (a largish "night light," not just its own indicator) so I can't forget about it if it's turned on. If I turn off the lights to leave the room and it's still on, the light will be quite conspicuous.And upstream of all that, there is going to be a GFCI, a brand new one to be installed today.

author: thm_w
author_rank: Super Contributor
timestamp: November 17, 2022, 10:22:35 pm
content: Quote from: mcovington on November 17, 2022, 05:21:12 pmYes this is the smart way to do things.Another thing you could do is have your fume extractor on the same power bar, so if your iron/hot air is on, the fan is on.

author: mcovington
author_rank: Regular Contributor
timestamp: November 18, 2022, 01:48:23 am
content: I had the same thought about the fume extractor. I'm going to tape its own switch "on" and put it on the switched power strip. That will keep me from walking away while soldering equipment is energized. Even more so than the light.

author: Shock
author_rank: Super Contributor
timestamp: November 18, 2022, 06:03:38 am
content: Could change the front switch over to an illuminated one of a known origin, that will let you know it's on as well. Plus you can also harvest a decent power cord and rewire it cheaply.At least then you don't have physically unplug it. Having power switches on the strip at least avoids this. I know they are less common there but here switched outlets are standard.

author: mcovington
author_rank: Regular Contributor
timestamp: November 18, 2022, 02:00:46 pm
content: Switched outlets are basically nonexistent in the US. I appreciated them when I was in the UK and Australia. Over here, you can build one if you really want (using a module that is a switch and a single outlet, that fits in the box that would normally house a double outlet). I haven't seen outlets that arrive with the switch already built in and connected. It would be a handy thing to have. In newer buildings I am seeing quadruple outlets in place of double ones, and that's a good move. In that setting, using one of the four openings for a switch would make a lot of sense. But it is absolutely not something I've seen done.BTW, there is a growing move in the US to install outlets upside down, ground pin up, for 2 reasons. (1) It no longer looks like a little face that appeals to children. (2) If something falls on a partly inserted plug, it will hit the ground pin first.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: November 18, 2022, 05:52:57 pm
content: @mcovingtonAs promised, my schematic for the Yihua 959D version 4 - per my reverse engineering whilst the UK was in Covid lockdown a couple of year ago. It is provided AS-IS and as such, should not be regarded asde facto; it's just myimpressionistic interpretationof what might be if such a thing was to exist as an open source design.I have also provided photos of the donor PCB top and bottom.I did not not mark up all of the component values, but you can get an idea of what they do by their location. If you can spot anything wrong/dire/bad/fatal in the schematic, let me know.Some notes:Of the PCB, there is nomains and not mainssectioning. Thus,the whole PCB should be regarded as a mains voltage sector. The heatsink on the triac is certainly a live part when the relay contact is closed by the opto isolator.CON9 is the ICSP port which was  used during production. Someone possibly unsoldered the connector after the programming/flashing cycle and solder bridged R37 to pull VPP to ground.On my device, the messy flux all over the microcontroller and lumpy soldering suggests it was hand soldered in situ (?) This was reflowed and cleaned.The overall build standard was fair to good, with plenty of red colored glue holding all mechanical parts in place.Postscript: I replaced the mains switch with a neon version, which required a slight replan of the cabling. Later when the pot needed replacing, I added a 0.1uF disc ceramic onto the base of Q3 to ground, to improve noise immunity.

author: mcovington
author_rank: Regular Contributor
timestamp: November 18, 2022, 10:03:00 pm
content: Many thanks!!!

author: jewelie
author_rank: Regular Contributor
timestamp: January 05, 2023, 03:54:21 pm
content: I (in the UK) just got a Yihua 959d this Xmas from Amazon sold by Yihua.I already dislike opening new and "expensive" things, and I hate modding them (a confidence and warranty thing I guess) but I made a deal with myself to push myself a bit out of that comfort zone: if I was going to buy this then I must open it, check it out, and do any significant safety mods if needed.In the main unit, there seems to be a minor PCB update to v4.1 (photo included below.) The only difference I can see is a cut-out in the board around the relay to presumably try to increase mains vs low voltage seperation? The soldering seems mostly quite neat, but I can see that the through-hole soldering, particularly on the component holding posts, hasn't flowed right the way through the vias (I'm not sure yet how badly this needs addressing?)In the (S218A-labelled) wand, there seems to be a different board (or maybe it's just the underside of it.) Inside of wand in second photo below. I seem to have a lower-current fan (150mA vs 200mA.) Also, on mine, the separation between the wire of the reed switch and the bare metal cylinder/shield was even worse.After probing the edge of the wire with a meter for continuity and discovering that bit really was lacking in any insultation where it was needed I decided to add some heatshrink (I don't know how well it'll cope with the temperature but I figured some attempt at improved insulation was better than none.) My dodgy mod in the final picture.Otherwise, the wiring checked out: live and neutral not swapped at any point (thanks so much for the schematic @AndyBeez, it made it easy to check that the relay was defintely switching the live and not the neutral), good earthing continuity where it's was intended to be, OC between the primary and secondary, etc.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: January 06, 2023, 05:52:24 pm
content: Thanks for the updated photos. The V4.1 PCB has an extra slot; commendable that someone was so conscientious with theisolation design. That mysterious CON12 is still there, so they weren't paying too much attention. Like mine, some of the parts on your photos look as if they were soldered in a school lesson; but at this price point, maybe they are? I agree, the reed switch lead is far too close to the bare metal chassis. However, your heat shrink's working temperature should outlast the ABS plastic handle if there is a blow back of hot air. Interesting the blower is 150mA not 200mA. Maybe it blows faster? Or mine just has the wrong label

author: efan
author_rank: Newbie
timestamp: January 21, 2024, 11:08:35 pm
content: I am in the UK i have the Yihua 959D with the 24V 0.15A fan has been unused for a year the fan stopped working and i get the F1 error when i last tried it.Having needed a hot air station again i started looking for a replacement handle or fan.Contacted Yihua on Amazon who want £30 for a replacement handle so had a look on Aliexpress and found replacement fans for £5 or £15 for the handle.Not sure if i want to risk buying anything just my luck for it to pop as soon as i plug it inDoes everyone still use this station and are happy with it for basic use