Author Topic: Yihua 959D hot air station - cautionary note  (Read 818 times)

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Offline mcovington

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Yihua 959D hot air station - cautionary note
« on: November 17, 2022, 03:14:12 am »
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.
 

Offline Shock

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Re: Yihua 959D hot air station - cautionary note
« Reply #1 on: November 17, 2022, 04:32:49 am »
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.



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Offline nigelwright7557

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Re: Yihua 959D hot air station - cautionary note
« Reply #2 on: November 17, 2022, 04:53:32 am »
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.
 

Offline mcovington

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Re: Yihua 959D hot air station - cautionary note
« Reply #3 on: November 17, 2022, 02:02:34 pm »
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?
 

Offline Shock

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Re: Yihua 959D hot air station - cautionary note
« Reply #4 on: November 17, 2022, 03:33:10 pm »
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.
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 189, 87V, 117, 112   >>> WANTED STUFF <<<
Oszilloskopen: Lecroy 9314, Phillips PM3065, Tektronix 2215a, 314
 
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Offline mcovington

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Re: Yihua 959D hot air station - cautionary note
« Reply #5 on: November 17, 2022, 05:21:12 pm »
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.
 
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Offline AndyBeez

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Re: Yihua 959D hot air station - cautionary note
« Reply #6 on: November 17, 2022, 05:26:21 pm »
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 soon when I get hold of the Kicad files.
« Last Edit: November 17, 2022, 05:50:47 pm by AndyBeez »
 

Offline mcovington

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Re: Yihua 959D hot air station - cautionary note
« Reply #7 on: November 17, 2022, 05:41:28 pm »
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_details

I'd really like to see that schematic!
 

Offline AndyBeez

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Re: Yihua 959D hot air station - cautionary note
« Reply #8 on: November 17, 2022, 06:32:40 pm »
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 the jet 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 heater must be 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 soldering :o

I 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.
« Last Edit: November 17, 2022, 08:45:18 pm by AndyBeez »
 
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Offline floobydust

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Re: Yihua 959D hot air station - cautionary note
« Reply #9 on: November 17, 2022, 07:38:41 pm »
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 have two three 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.
« Last Edit: November 18, 2022, 04:37:59 am by floobydust »
 

Offline mcovington

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Re: Yihua 959D hot air station - cautionary note
« Reply #10 on: November 17, 2022, 07:50:42 pm »
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.
 

Offline thm_w

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Re: Yihua 959D hot air station - cautionary note
« Reply #11 on: November 17, 2022, 10:22:35 pm »
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.

Yes 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.
Profile -> Modify profile -> Look and Layout ->  Don't show users' signatures
 

Offline mcovington

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Re: Yihua 959D hot air station - cautionary note
« Reply #12 on: November 18, 2022, 01:48:23 am »
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.
 

Offline Shock

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Re: Yihua 959D hot air station - cautionary note
« Reply #13 on: November 18, 2022, 06:03:38 am »
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.
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 189, 87V, 117, 112   >>> WANTED STUFF <<<
Oszilloskopen: Lecroy 9314, Phillips PM3065, Tektronix 2215a, 314
 
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Offline mcovington

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Re: Yihua 959D hot air station - cautionary note
« Reply #14 on: November 18, 2022, 02:00:46 pm »
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.
 

Offline AndyBeez

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Re: Yihua 959D hot air station - cautionary note
« Reply #15 on: November 18, 2022, 05:52:57 pm »
@mcovington

As 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 as de facto; it's just my impressionistic interpretation of 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 no mains and not mains sectioning. 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 [likely] 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.
« Last Edit: November 18, 2022, 05:58:06 pm by AndyBeez »
 
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Offline mcovington

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Re: Yihua 959D hot air station - cautionary note
« Reply #16 on: November 18, 2022, 10:03:00 pm »
Many thanks!!!
 


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