8586 858d Hot air station 2in1 Help Please - Page 1
Forum section: electronics / repair

author: Quantum1
author_rank: Newbie
timestamp: May 14, 2024, 11:55:34 pm
content: Hi all. Was wondering if someone could help me with this 8586 hot air unit. Its basically same as the 858d but with added soldering iron. Anyway, When I turn it on via rear switch, I hear a small buzzing from the fan. This is without turning on any of the front 2 switches. Then when I turn on the front switch for hot air, the fan starts and heating element turns on. The pot on the front that increases and decreases fan speed also works as normal. But the display reads zero and only goes up to about 26 degrees when the hot air is fully hot. Then when I turn off the front switch, it's supposed to turn off heating element and run the fan for a little while to cool everything down, but it does not do this either. It either turns everything off and goes back to fan buzzing, -or- it turns everything off except the heater. I know this is a weird complicated problem, but if anyone can point me in the right direction it would be a great help.Btw, I measured the fan while its off and buzzing. It's at 1.6v. Also, checked the thermocouple with multimeter which is at around 2-3 ohms when ambient and goes up when heated. Measured the low voltage (diode) side on optocoupler and getting voltage drop of 0.5v one way and 1.4v the other direction. Is this normal for the optocoupler? Another thing is I measured the R40 resistor coming from pin1 of MOC3023 optocoupler and it reads 900k ohms when its supposed to read 4.7m ohms, but when removed from circuit, it reads as normal - 4.7m ohms, so I soldered it back on(pic on bottom with red arrow). Also checked another resistor R37 next to triac (pic below with blue arrow) and it reads 75 ohms in circuit but it reads the normal 330 ohms out of circuit. I have checked all other resistors and they're all reading normal. Im thinking there's a semi short somewhere or a bigger component is bad but this is my first time messing with this kind of circuit and am not too familiar. Please help and thank you in advance.

author: AndrewEp17
author_rank: Contributor
timestamp: May 15, 2024, 02:20:54 am
content: It sounds like it could be the thermostat/temp sensor in the heat gun is failing

author: Quantum1
author_rank: Newbie
timestamp: May 15, 2024, 03:13:42 am
content: Hi Andrew. Thanks for replying. I checked the temp sensor and it’s fine. It’s definitely something on the board itself. I’m leaning towards the LM358 thermocouple op amp, but how would I test it to see if it’s bad?

author: AndrewEp17
author_rank: Contributor
timestamp: May 15, 2024, 03:09:32 pm
content: I don't have much experience with op amps but maybe you could try removing it from the unit and making a test circuit with it. There should be some tutorials or schematics on google you could try

author: AndrewEp17
author_rank: Contributor
timestamp: May 15, 2024, 06:13:21 pm
content: I could be wrong but i think the heating element is powered by mains voltage and if the temp sensor touches the heating element it would put that voltage into the temperature circuit and damage the op amp. I think I've blown up a heating station like that before haha.