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Electronics => Repair => Topic started by: sampler1 on July 07, 2020, 12:46:03 am

Title: Hot Air Station - Komec 908 Burned up
Post by: sampler1 on July 07, 2020, 12:46:03 am
Hi all,
I have a Komec 908 Hot Air Rework station . It went up in smoke.. The OEM manufacturing installed a 15 amp fuse on the primary of the transformer instead of a 1.5 amp.. The transformer shorted and well you can guess.
I have repaired all but the rear control board for the Hot Air has two resistors R7 and R10 that cannot be identified. Totally black and burned.
Can anyone help me out with there value. I dont want to guess.
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Title: Re: Hot Air Station - Komec 908 Burned up
Post by: SpecialK on July 07, 2020, 02:46:20 am
My guess is something in the range of 10 ohms to 200 ohms. Super low value (less than an ohm) wont heat much with heavy current due to I squared R.   High value (kilo-ohms, megohms) wont go supernova due to V squared over R.  Obviously something else had to short in the circuit to subject these resistors to high voltage or current.  I'm guessing that's the fan motor?

R1 and R2 are 150 ohm.  So that's my wild guess
Title: Re: Hot Air Station - Komec 908 Burned up
Post by: sampler1 on July 07, 2020, 08:06:32 pm
Quote from: SpecialK on July 07, 2020, 02:46:20 am
My guess is something in the range of 10 ohms to 200 ohms. Super low value (less than an ohm) wont heat much with heavy current due to I squared R.   High value (kilo-ohms, megohms) wont go supernova due to V squared over R.  Obviously something else had to short in the circuit to subject these resistors to high voltage or current.  I'm guessing that's the fan motor?

R1 and R2 are 150 ohm.  So that's my wild guess

Thanks but Hummmmmm..
Title: Re: Hot Air Station - Komec 908 Burned up
Post by: sampler1 on July 07, 2020, 08:10:32 pm
The transformer was 24v 1.5A for the Iron and also 10V 0.8a for the hot air controller board. The transformer has already been changed. As for as those two resistors I was hoping to get lucky here. If not ill hook up two decade boxes and figure it out. I have Perdition's Flame up my ass!
Cheers

_________________
Title: Re: Hot Air Station - Komec 908 Burned up
Post by: SpecialK on July 07, 2020, 09:36:17 pm
so do we know where the resistors are connected?  Like are they in the path of the soldering iron heater, or the fan for the hot air?  I might have a chance to look at my Sparkfun hot air tomorrow but it's strictly a hot air, no soldering iron.
Title: Re: Hot Air Station - Komec 908 Burned up
Post by: sampler1 on July 08, 2020, 12:34:28 am
One is connected to pin one of a Triac and the other pin one of an IC LM324N.
all is on the Hot air side. I already have the Iron working.
Thanks
Title: Re: Hot Air Station - Komec 908 Burned up
Post by: TheMG on July 08, 2020, 12:45:26 am
Looks like the TO220 part (TRIAC?) on the board has let the smoke out too. I wonder where the optocoupler comes into play in the circuit? Doesn't seem to have spared the rest of the circuitry from damage so it may not be for isolation?

Anyways, if I had to guess what happened here, the TRIAC failed causing a cascade failure which eventually ended up with the transformer burning up. Very bad circuit design if that is indeed the case.