Atten 8586 tip is glowing red

[crx991]

Hi,
I need your help guys. I have an Atten 8586 for some years and it's working great until the latest days during a soldering work the tip start becoming glowing red... 
I've noticed that the tip becomes red incandescent when I set a temperature higher than 300° C.
Plus if I put the station at max temperature, 480°C, the display show that the current temperature is 422°C circa and hangs...
So i'm assuming that there's some "temperature reading" problem with the central unit (it does the same thing even with a new soldering iron).
Hopefully i was clear, can someone can help me, give and advice, etc?
I know it's a cheap cinese junk, but now i can't afford new charges for a new, and better soldering station.... 

Thanks

P.S.: If you need photos, you can see in this post here . I think -N-  taked great photos

[un4tural]

If you're going to repair it, open it up and check for anything visually wrong, hopefully its a cap or some jellybean component gone bad and not the main cpu or whatever it has. further than that you'd likely just need to reverse engineer ( check traces its probably single layer) the sense circuit and see if you can find anything obvious. That's as far as i know how to do it without a schematic, sorry 

[amyk]

Check the triac.

[crx991]

Thanks for the responses guys.
The main CPU, better to say MCU, it's an 16F916. I don't think it's damaged. The hot air gun works great, the problem is only with the soldering iron....

Check the triac.

Yeah @amyk. I was thinking the same thing. Maybe a faulty Triac, or some shitty soldering job....



EDIT: OK, triac is overheating. So i'm thinking this should be the main cause. The problem is that i can only find an bt139-600 at my local shop. The original atten triac is an bt137-600E. Now looking at the datasheet there's wrote:
"This sensitive gate "series E" triac is intended to be interfaced directly to microcontrollers,
logic integrated circuits and other low power gate trigger circuits."
Can someone can help me if the bt139-600 it's a valid alternative, or there's a big difference between them?

[amyk]

A BT139-600E would work and probably be better since it has higher current capacity, but the non-E ones might not because they require much higher triggering current (compare the datasheets.)

[Seekonk]

I'm not thinking triac at all.  This is an offset in temperature.  Either in the the electronics or the sensor.  If thermocouple, perhaps the bead has broken and an oxide layer is conducting.  I would do a resistance check first.

[crx991]

A BT139-600E would work and probably be better since it has higher current capacity, but the non-E ones might not because they require much higher triggering current (compare the datasheets.)

Ok thanks for the info mate. I've already ordered a new BT137-600E. Hopefully it will arrive soon as possible

I'm not thinking triac at all.  This is an offset in temperature.  Either in the the electronics or the sensor.  If thermocouple, perhaps the bead has broken and an oxide layer is conducting.  I would do a resistance check first.

Do you think? The triac becomes really hot.
If i'm not wrong the thermocoulple should be in the soldering iron. Even with a new one I have the same problem....
Strange fact is that the that the tip becomes red incandescent only when I set a temperature higher than 300° C, and even at the lower temperature, 200°C, tip can easly melt solder, which is not normal.
There's something that i can check?
I apologize for my bad English and inexperience in the field. I am still a rookie

[Cubdriver]

It sounds to me more like a sensing/temp feedback issue than the triac, based on the fact that it still seems to CONTROL the temp, the issue is more that the temperature it's controlling at is too hot.  I'd expect the triac to fail shorted (iron to full temp no matter the setting) or open (iron cold no matter the setting), rather than a temp offset.

I'm with Seekonk - see if you can find info on the sensing circuitry and check it out - it could be a bad temp sensor, or one that's lost thermal continuity with the part of the iron it's supposed to be measuring, causing it to heat up more to get the sensor sufficiently hot to make the setpoint.

Good luck with it!

-Pat

[Cubdriver]

Wait - I just re-read the post above mine - are you saying that you've plugged a different iron into the power supply, and that one behaves the same way?  If so, that would not change my suspicion that the problem is in the sensing circuitry, but would prompt me to look for that problem in the soldering station itself, rather than the iron.

Take a good look at the connector for the iron where it attaches to the station, and see if you can trace out the temp sensor circuitry within the station itself - the issue may be there.

-Pat

Oh, and no worries about your English - it's far better than some I've seen on other forums that's posted by people who supposedly speak it as their only language!

[crx991]

Thanks for all the replies and the support guys 
Yes, i will also start searching for broken tracks, cold\bad joint or broken components.

[Seekonk]

I've got an old HexAcon stand.  On an impulse when buying some other stuff,  saw a Hakko 936 iron replacement for $3.05 that I bought.  Got to be crap, but I thought I would add a boost converter and use it at my 12V camp.  I had done some research and the Hakko copy schematics all had an op amp with two pots for lower and high range.  Even with a micro there will still need to be an op amp to boost the sensor up.  Never found a schematic for yours.  You could mark the pots with a marker and give each a twiddel in case it got erratic at that spot.  If it goes down to 100C, boiling water could be used as a reference and you could use melting temp of your solder for upper reference.

[crx991]

I've got an old HexAcon stand.  On an impulse when buying some other stuff,  saw a Hakko 936 iron replacement for $3.05 that I bought.  Got to be crap, but I thought I would add a boost converter and use it at my 12V camp.  I had done some research and the Hakko copy schematics all had an op amp with two pots for lower and high range.  Even with a micro there will still need to be an op amp to boost the sensor up.  Never found a schematic for yours.  You could mark the pots with a marker and give each a twiddel in case it got erratic at that spot.  If it goes down to 100C, boiling water could be used as a reference and you could use melting temp of your solder for upper reference.

If i'm not mispelled, looking at this image the IC2 (the black dip8 chip) should be used as sensor circuit. It's an LM358P. Can be the cause of bad reading?

[Seekonk]

I think that would be an unlikely failure.  I would measure the voltage at the power pins of it.  There are no pots to adjust so the voltage would be critical for setting the offset.  A power supply cap could be bad resulting in a lower supply voltage even after the regulator.  Since it feeds the micro it should be a standard voltage.  We have all seen Dave's videos showing micros will still operate at lower voltages.  It is a long shot , but can't come up with anything else without a schematic.

[crx991]

Yeh, in the end I thinks it's more convenient play directly with thetrimmer. As you ca see from this image there's two pots, one for the hot air and one for the soldering tip...