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I am trying to understand a soldering iron PCB circuit. I am trying to use a different range circuit for my prototype.

Can someone please elaborate how it is controlling the temperature?

Secondly, I am unable to get any details of D8 (blue component near LED) as C32 written on it.

PCB TOP Side Image PCB Bottom Side Image Hand Drawn Circuit

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    \$\begingroup\$ Start by tracing out the circuit and drawing the schematic. You may have to do this three times or more to get it into a sensible layout. If you mirror the image of the underside of the board it will be easier. There is a schematic drawing tool on the editor toolbar so you can add your attempt into your question. \$\endgroup\$
    – Transistor
    Commented Apr 8, 2021 at 6:31
  • \$\begingroup\$ Since D8, begins with a D I would say it is a type of diode. \$\endgroup\$
    – Emre Mutlu
    Commented Apr 8, 2021 at 7:40
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    \$\begingroup\$ How ironic that they did a poor soldering job on the soldering iron PCB. \$\endgroup\$
    – Lundin
    Commented Apr 8, 2021 at 13:16
  • \$\begingroup\$ Can we get this guy some upvotes for actually doing the work and coming back with a decent schematic pls? \$\endgroup\$
    – K H
    Commented Apr 12, 2021 at 0:02

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I'm not going to trace it out, but it doesn't really look like a temperature controller at all. Looks more like a phase control that's only slightly more sophisticated than a light dimmer (reduced snap-on).

The diode may be a 32V diac similar to DB3, in which case the TO-92 part U10 would be something like a MAC97.

Edit:

Based on your schematic- this is a simple phase control. The pot adjusts the trigger angle. The trimpot is used to trim the minimum power setting. The bridge and R25/26 are used to help reset the timing capacitor C1 to reduce "snap on" effect. The time constant is between the pot/trimpot,R and C1.

When the voltage across C1 exceeds about 32V it triggers on, triggering the triac. Image from here:

enter image description here

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  • \$\begingroup\$ Thanks Spehro, yes its a temprature controller and U10 is MAC97A6. I am not sure about the functionality of diode D8 (blue) which you suggested as diac. Can you please explain it a little. \$\endgroup\$
    – Iffi Hus
    Commented Apr 8, 2021 at 9:06
  • \$\begingroup\$ @IffiHus I doubt it's a temperature controller because there's not enough wires for that. The blue/red is connected together and clearly marked Neutral. The black/other red pair looks like the supply/switched output and the green ones are just earth. So where's the temperature sensor? Likely just phase control as said. \$\endgroup\$
    – Unimportant
    Commented Apr 8, 2021 at 10:44
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    \$\begingroup\$ It's a power controller, not a temperature controller (there's no sensor). You can look up the functionality of a diac. Here is a datasheet. It simply breaks down and latches when the voltage (in either direction) across it exceeds some threshold. That triggers the MAC triac, once every half-cycle of the mains. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Apr 8, 2021 at 16:24
  • \$\begingroup\$ Thanks Spehro, there is no temperature sensor. P1 is AC L, P6 is AC N. P4 and P5 are heater leads. Actually I just draw the circuit of the PCB but I don't know how to attach it here. Can you please guide me how to attach it here or share your email so that I can send the hand drawn schematic to you? It would be a great favour. \$\endgroup\$
    – Iffi Hus
    Commented Apr 9, 2021 at 5:04
  • \$\begingroup\$ Upload it to an image site such as imgur.com, and put a link in your question if it doesn't allow you to directly insert an image. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Apr 9, 2021 at 5:20

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