Hakko 850 hotair repair ?

[KD0CAC John]

I picked up a used kinda working Hakko 850 hot air station and when working on the higher end - heat & air it seemed ok ,
but when I was lower heat & air it would would overheat .
I would guess that is should have a temp regulator - used some sensor feedback and is not working .
I haven't looked , just assumed that getting a wring diagram / schematic may not be available , some suggestions on getting working again when using lower heat & air settings ?

Thanks John 

[nanofrog]

Attached is a .pdf of the schematic for the Hakko 850B, 120V model (rather simple schematic built around a 555 timer & a upc1701c zero voltage switch).

Hope this helps. 

[KD0CAC John]

Thanks
I took apart & removed board to check for obvious issues , nothing found .
Cleaned the points on the relay - I use dollar bills to rub on points .
I forgot to mention that I was using one of the reducers , I have 4 sizes and was using the 2nd from the smallest on some SMD parts .
It may have been working correctly , but too much heat & not enough air ?
When I opened & inspected I operated with the reducer off , noticed that the heating element pulsed with the same frequency as the light next to the heater control , then as I adjusted from lowest to highest the frequency varied .
I do not think there is a feedback to limit too much heat , only 3 wires one to case for ground , not enough for sensor / feedback .
I have a copy of the Hakko , a Yoyue 850 that one of these days I should post some pictures to show where the copy cheaped out .

[KD0CAC John]

Messed up again , or the 1st time , noticed the diagram did not match my unit , then noticed that the diagram was for an 850B , and I did not note mine is the 850A model ;(

[nerdalert]

here is hakko 850 troubleshooting guide service manual

[KD0CAC John]

Thanks , my issue is not in the pdf , but good to have .
I need to show some pictures of the 2 Hakko 850 and the Ayue , its obvious where the making cheaper happened .

[nanofrog]

I need to show some pictures of the 2 Hakko 850 and the Ayue , its obvious where the making cheaper happened .

I think this would be really helpful.