Author Topic: Yihua 853D soldering station - details about fan circuit repair, incl. schematic  (Read 1421 times)

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Offline mosagepa

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Hi there all EE vblogers!

I've seen other threads here regarding internal details and some repairs on this kind of units.

My 853D stopped suddenly blowing hot air, I suspected the fan. So first I rushed to buy a replacement, although later on it turned the TIP122 was to blame. Don't know even why it failed on me!

Anyway, here are the details I've gathered in this experience.

My subsequent posts in this thread include up to now the following:

- First off, internal PCB overall views
- Schematics  (of the fan control section only for now, but I'm recollecting more sections and hand-drawing them for my own notes.)
- Pictures of section in the test bench with lil' breadboard for controlling fan and test
- Full size FRONT and BACK (mirrored for you to align if you wish) views of the full PCB.

In the first 2 pictures we'll see the PCB just as the unit was opened, with all the harnesses to/ from panel and different subsystems still in place.

As anyone familiar with these units might know, they have been several revisions (or should I say clones and re-clones, even between various Chinese suppliers themselves ---oh well, competition is good they say!).

My particular 853D has NO RF sensor in the front panel, but otherwise looks externally identical to many ones with same model designation. I got this from Amazon, not AliExpress or the like (yeah I got Prime and was quite eager those days to get it!)

Here follows --again, just for THIS particular PCB revision, silk-marked as "853D-8S19-V3"-- a summary of the purpose of the connectors you've seen in the previous two pictures:

[ ---- to be updated --- ]
« Last Edit: September 06, 2021, 10:59:43 am by mosagepa »
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Offline mosagepa

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Overall pictures re-posted here with lower resolution so as not to deprive resources :)

Offline mosagepa

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Edited first message to add the PCB silk-name: "853D-8S19-V3".

I haven't seen similar PCBs in all other threads I was browsing thru my initial quest for info.

If anyone out there bought his 853D from Amazon or some other "non directly Chinese distributors", maybe got the same PCB model, let me know please.

CNs on this main board:

Code: [Select]
  --> Left to Right on TOP EDGE:
CON15 (3-pin)  [BROWN-WHITE-GREEN]       from/ to HANDLE FAN
pin 1: [BROWN] (square pad) =  FAN+ (RED from FAN inside HANDLE)
pin 2: [WHITE] GND          =  FAN- (BLACK from FAN ins. HANDLE)
pin 3: [GREEN] CON10 pin 13 =  FAN SENSE (YELLOW from " " ins.")

CON1  (3-pin)  [BLUE-YELLOW-RED]         from/ to HANDLE HEATER
pin 1: [BLUE] =   to mini-PCB inside handle, 'SENSOR' pad
pin 2: [YELLOW] = to EARTH lug for heater inside handle
pin 3: [RED] =    to mini-PCB inside handle, 'HANDLE' pad

CON9  (power,2-pin)   [GREY-TRANSP]      to IRON HEATER  (24VDC ???)
pin 1: [TRANSP.] = to HEATER active voltage input
                pin 2: [GREY]    = to mini-PCB inside handle, 'GND' pad
  (NOTE: also connected inside, to heater's EARTH lug.)

CON14 (power,2-pin)   [BLACK-RED]        AC (post-fuse) to Transf.
CON12 (power,2-pin)   [RED-RED]          from Transf. INPUT
CON2  (power,3-pin)   [RED-WHITE-BLACK]  from Transf. 20V-10V-0V OUT
CON5  (power,3-pin)   [BLACK-WHITE-BLUE-n/c]  from ext. trans. 2N
  --> Top to Bottom on LEFT EDGE:
V2    (3-pin)  [WHITE-WHITE-WHITE, red marks] from PANEL FAN POT
CON11 (4-pin)  [RED-RED-YELLOW-YELLOW]  from Transf. 30V & 10V OUTs
CON8  (2-pin)  n/c ???
  --> Left to Right on BOTTOM EDGE:
CN10  (sic) (long; 13-pin)  from PANEL (identify component lines!!!)
CON4  (5-pin)  [WHITE-WHITE-n/c-BLACK-RED]  to/ from IRON SOCKET
CON6  (2-pin)  [BLUE-BLUE]  from Transf. 24V OUTs
CON3  (3-pin)  [WHITE-WHITE-WHITE, red marks] from PANEL DC SOURCE POT.
pin 1 (square pad): to TL431 volt.reg.ctl. (for DC Source)
pin 2: to U3-A (LM358) Pos. Input
pin 3: GND
CON13 (2-pin)  [WHITE-WHITE, red marks]         to PANEL RED LED
CON7  (power,2-pin)  [BLACK-RED]                to PANEL DC METER

« Last Edit: September 06, 2021, 10:33:25 am by mosagepa »

Offline mosagepa

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Here comes picture of the labelling on the fan that "failed" (I made sure I got the precise same labelled replacement, this time yep it had to be from AliExpress).

As you may notice, this have 3 wires, (red-black-yellow), but it's NOT a brushless motor. The driving circuit as we'll see in my home-made schematics is just a TIP12x-activated circuit, very common and easy to understand.

Although the transformer yields 30V and 10V (AC, rectified by respective 1n4007 bridges), the fan is 24VDc nominal. A convenient zener in the circuit limits the maximum attainable feed into it (see schematic).


Offline mosagepa

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Here comes the hand-drawn schematic of the part of PCB that controls the fan blower.
It includes: TIP120 (replaced the former TIP122, only difference is TIP122 allows for max. 100V, TIP120 "just" 60V.)  Both rated 5A max I think;  2x2N3904-kind SMD for control. The Zener, and the front panel POT (B-10k) which is interposed with a 15k to control the range of fan velocities.

I'll try to pass this hand-drawing to a more decent, say Kicad or some medium if I get the time.

You're free to comment anything, or ask questions about this station. I'm willing to answer or locate anything you need or are interested in this PCB or unit.

(In fact it's way best and easier NOW that I have ti fully opened and in my bench...)

I'll keep posting further details and pictures of it.

Kind regards.


Offline mosagepa

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Now let's describe a bit operation of this part of the unit, the fan control schematic, for anyone interested (although a lot of forum followers here will find it almost self-explanatory):

I'll paraphrase/ adapt/ reuse here a quite plain description found here for a similar model (858D), for it mostly applies here with a mere re-annotation of components:

"The fan is controlled through transistor U9. The fan is rated for 24V, but the supply voltage is a bit more
than 30V. The circuit has to make sure that the fan is not overloaded. The microcontroller can use
transistor Q13 to drain the base current of U9 and turn the controller off this way. If Q13 is turned off,
the speed control is implemented through Q14 and the surrounding circuit. The more Q14 is conducting, the more the base current is drained and the less U9 is conducting. However, Q14 cannot drain U9 completely, as the emitter voltage of Q14 always sits one diode drop above ground level."

"POT (B10K) which is the front-panel potentiometer, can be used to control the voltage divider between R55 and R59.
The higher the voltage at the taper of the potentiometer, the higher the base current of Q14, resulting in
less conductance for U9. In addition the aforementioned voltage divider and the transistor form a feedback loop to control the base current of U9, and in result the voltage on the fan."

« Last Edit: September 06, 2021, 10:34:35 am by mosagepa »

Offline mosagepa

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Some pictures for fun, of my "bench" when I was testing just this part of the PCB.

To test just the fan feeding section, it suffices to connect headers:
- V2 (3-pin) to the Panel POT B10kOhm  (using original harness)
- CON11 (4-pin)  (red-red-yellow-yellow)  which feeds the 30V, 10V AC respectively from the transformer into the PCB.   (again original harness)
- CON14 (2-pin)  (black-red)  (gross wires, original)  These are the mains wires that come from the fuse assembly into the PCB.
- CON12 (2-pin)  (red-red) (gross wires, original)  "copies" CON14 points to the outside of PCB towards the transformer's main AC input
- CON15 (3-pin)  (brown-white-green)  (FAN+, FAN-GND, and FAN "sense" wire, respectively).

Now about the replacement fan wiring (the original one I dismantled even if original TIP122 was suspected and replaced, too).
As it came with just stripped wires, I had to make a JST-to dupont 3-wire harness to feed it adequately. Notice that the yellow wire I am not using in this "experiment" to test the fan.

One of the pictures show a little breadboard which serves me to feed +5V / GND signal using the pushbutton.  If you feed GND to CN10 pin 9 on the PCB,  the fan runs at a speed regulated by the POT. If you feed CN10 pin 9 with +5 volts, the fan stops as explained in the above post.

CN10 pin 11 is GND.  You can see the duponts attached there.


Offline mosagepa

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Oops, missed the pushbutton little PCB for testing pic. Here it comes.

Along with aligned FRONT and BACK (mirrored) pictures of the PCB for you to analyze and drool over  :popcorn:


Offline mosagepa

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I present my excuses to anyone that feels my hand-drawn schematic is weird. Also I must point out to the fact that some components seems re-soldered (in a provisional way), see that 2W resistor for example which is tied grossly.

(I had to take some components apart like those big Rs and then refit them, as they didn't allow me to clearly see marking on SMDs and stuff...)

I am yet to clean things up and close the unit one of these days. So feel free to comment anything before that.

About "cleaning", don't get me started about the TONS of flux residue that were on both sides of the PCB!!!  Spent quite a time taking off most of it.  It's really shameful how you can receive some items from Chinese cheap assemblers... I got once an FPGA development board that got so many residue you just couldn't clearly tell out some of the pins!
« Last Edit: September 06, 2021, 12:33:43 pm by mosagepa »

Online fzabkar

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The base of Q14 is held at 8.8V by the zener and Vbe (8.2V + 0.6V = 8.8V). The base is connected to the wiper of the pot. The fan voltage is then determined by the resistances in the potential divider formed by the three resistors.

When the pot is set to minimum, the fan voltage is ...

    37K / 22K x 8.8V = 14.8V

When the pot is set to maximum, the fan voltage is ...

    37K / 12K x 8.8V = 27.1V

The maximum dissipation in the Darlington pair occurs at minimum fan voltage, so ...

    Pmax = V x I = (30V - 14.8V) x 0.2A = 3.04 watts

It seems to me that the transistor is more than adequately rated for this application (65W).

Would it be worthwhile to add a reverse biased 1A 60V (?) Schottky rectifier across the fan terminals as a back-EMF snubber?
« Last Edit: September 08, 2021, 05:48:45 am by fzabkar »

Offline mosagepa

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Many thanks @fzabkar for your input and prospective calculations.

Where do you get/ infer that the Zener is actually 8V2?  Maybe the markings on the pictures?  (I don't have perfect eyesight sorry)  I must confess I didn't measure it  (heck, I am not that used even to *any* testing of Zeners, at least in-circuit,  so a side question is: how could I actually measure it?)   I mean, without powering the PCB, of course.

It's strange that the circuit would allow, according to your computations, more than 24 volts applied to the fan, since it's rated nominal 24V and normally one would not even want to drive it at full voltage, only a tad less  (to allow for tolerances and the like.)

The TIP120 I've soldered replaces a former TIP122. I know both would happily allow this small a load, and all ratings for this precise design. In any case, the fan label warns "0.2A" so it would be good exercise to check that's indeed the case here...?

Do you happen to own a 853D/D+?
« Last Edit: September 08, 2021, 12:19:40 pm by mosagepa »

Online fzabkar

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DZ1 in the original schematic is 8V2 (8.2 volts).

It wouldn't be possible to measure the zener in-circuit without powering it.

I don't own an 853D/D+.

Edit: The calculations assume that the base current drawn by Q4 is much lower than the current in the divider resistors.
« Last Edit: September 09, 2021, 03:54:30 am by fzabkar »

Offline mosagepa

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Oh I see, that schematic I remember, is from 858D ("original" as you mention).

Differences are mainly, that the 853D+ I own uses 30V. The transformer is a bit different and has differing output branches from the 858's. Also the voltage divider around the pot has bit different values. Base resistor to the overall on/off transistor maybe doesn't affect too much.


Online ozkarah

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I have a Yihua 853D (15V 2A version). Today the auto-stopping (when the handle is put to the dock) function of the hot air gun stopped working.

It continues to heat the air gun while the handle is in its dock until set temp is reached. Cooling down never starts.

I checked the magnetic sensor and the wire it comes from the sensor to the board (CON 1 blue wire). They seem to be okay. When that handle is in the dock, the blue wire is grounded. And vice versa. It is not grounded when the handle is removed from the dock. 

Apart from the auto-stop function, the rest seems to work okay:
- Heating stops when the set temperature is reached (but cooling down does not start till I manually turn off the hot air switch).
- If I manually turn off the hot air gun switch, the cooling down starts, and the fan stops at 100 degrees Celcius. 

Do you have any idea to fix the problem?


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