Yihua 992DA+ Hot air gun and soldering rework station, burnt mark

[Peter_1402]

Hi Everyone,
I bought a Yihua 992DA+ hot air gun and soldering iron unit from a used market.
1. Soldering iron works great
2. There is a burnt mark on the hot air gun handle.
I am a bit concern by the look of the melted plastic. I opened the hot air gun handle and took some readings with a multimeter.
Heating element ~ 75ohm. (Similar reading taken from a spare heating element that came with the unit.)
Thermocouple ~ 1.5ohm. (Similar reading from the spare heating element.)
Reed switch tested ok with a magnet.
From the above test, I can conclude that the hot air gun handle is OK. So, the fault maybe in the control box.
1. A multimeter test on optocouplers seem OK. What if they are intermittent? Should I just go and replace the two part?
2. The two TRIAC look OK. Should I replace them too?
3. What are the possible faults with thermocouple and reed switch signals not being processed?

Thanks in advance.

[stj]

i have done that with high heat, low airflow and a small nozzle,
it may work fine

[Peter_1402]

stj, I have missed out one important info i.e. seller told me that the heating element is weak so need to replace it. At the hot air gun is unusable.

[stj]

"weak" ?
it's just a wire, it's either intact or broken.
did you test it? it maybe an airflow issue.

[Peter_1402]

stj, I did ask him about air flow and he said the air flow is OK. Only thing is the temperature cannot go beyond a certain degree. This is what he mean by weak. Thanks.

[stj]

sounds like a control circuit issue
you can test this by putting the air to maximum and forcing the element on 100%- keep a finger on the power switch though.
another possibility is a break in the cable - it does get moved a lot.