Hot air rework station overheating

[AlenZGB]

Hello,
I buy some cheap hot air rework station and customer said that heater blown,i opened it
and i saw that heater isnt good, so i order new one, but when i connect it and turn the
hot air station on minimal temp, heater goes so hot that he turn red and blown again
in few sec.
Now my question is, what exactly is controlling temperature of the heater except potenciometr and how to check it. I open the board and saw few melted solder joints.
Any help with that is welcome.

 

[AlenZGB]

 

[(*steve*)]

(a) it looks like it has gotten wet

(b) the toroid looks like it has gotten (too) hot. If this is shorted (depending on how the circuit works), this may be your problem.

(c) I would check the triac or mosfet in the TO-220 case (3 legs and a metal tab)

(d) brownish, or darkened discoloured areas of the board indicate where things have gotten hot. Aside from the triac or mosfet and the inductor, can you identify any other components on the side opposite the discolouration?

 

[AlenZGB]

Thanks for fast replay.
Ill look in those thing you tip out.

Other thing look ok, except one thing, on the 2nd picture with components looking up. on the left side of the board i think its resistor ( grey with yellow, brown, white colour marking) is very loose, that may also be the problem.

And is there any reference voltage or resistance output where heater should come?
so that i can messure it.

 

[(*steve*)]

Other thing look ok, except one thing, on the 2nd picture with components looking up. on the left side of the board i think its resistor ( grey with yellow, brown, white colour marking) is very loose, that may also be the problem.

Is that the one with black heatshrink on the leads? If so, it is only the stiffness of the wires that hold it in place. The solder connections look OK. It is possible it is physocally damaged, but I can't see anything from the photos you've posted.

Actually, I was looking at the other end of the board. The resistor near the toroid looks damaged, and the resistor you've mentioned looks like it has gotten hot.

If the wires can be seen moving on he other side of the board then the solder connection is broken or a dry joint.

And is there any reference voltage or resistance output where heater should come?
so that i can messure it.

It's hard to tell. Can you read anything on any of the ICs?

 

[AlenZGB]

I know pictures are a bit bad, i took tham with my phone, im at work now but when i come home ill clean all of and took pictures with camera.
and will edit and circle components that i think are bad.
But it has many blacked solder joints, and that big resistor i was talking about is for sure got to hot.

I try to messure the output and when i turn to AC V i got from -3 to 3 v
randomly switching.

 

[AlenZGB]

more pictures and i hope better quality

 

[(*steve*)]

*WOW* That's pretty horrid construction.

I'd replace all the power resistors, and resolder every connection on the board. I'm not confident that they've been done properly.

Note how there is *no* solder n the lead that has broken away from the solder. That's a sign of very poor soldering and possibly the lead was never actually soldered (the solder did not bond to the wire due to it being corroded perhaps)

 

[AlenZGB]

ill try to replace all bad resistor, should i replace the toroid to ?
i check it with DMM and connection is ok, wire didint broke but maybe the melted isolation can be a problem.

 

[(*steve*)]

On closer inspection, the toroid *may* be OK.

But check for yourself. Look closely and try to see if any of the insulation is damaged.

If you have to, desolder it and unwind a couple of turns to see if the insulation has been affected on the inside.

You need to remember exactly how many turns you unwind so you can wind them back. This isn't much of an issue if you unwind 1 or 2, but if you unwind a lot (or if you have to rewind it with new wire) the number of turns is important.

Don't discard any parts you remove. Some of those resistors may have gotten so hot that their resistance has changed as well as the colours on them. It may not be immediately apparent what the correct replacement should be.

 

[AlenZGB]

I order new heater today, week or two untill arival.
Till then i have time to fix first problem.
If resistor gotten to hot and colour changed how can i know which one should i buy,sounds like a tricky one to know, or is there any way to find that out except
schematic which i couldnt find on the web.

Edit:
Any identification for toroid ?
part number or winding turns or specification that i can look when i buy new if needed ?

 

[(*steve*)]

If resistor gotten to hot and colour changed how can i know which one should i buy,sounds like a tricky one to know, or is there any way to find that out except schematic which i couldnt find on the web.

Desolder the resistors and read their resistance. Then try to determine what the original values were from what the bands look like.

It's not trivial, but if you assume that the resistance will only go up, and that there are a limited number of preferred values, you should be fine. Chances are the colours can still be read. I'll take a closer look and see what they look like to me.

Any identification for toroid ?
part number or winding turns or specification that i can look when i buy new if needed ?

Unlikely to find an identifier. However it is unlikely that the core is damaged. At worst you need to get some wire of the same gauge and wind the correct number of turns onto it.

 

[AlenZGB]

Ill try to inspect closely all components and replace bad ones.
Then ill have to wait for heater.

Thanks for tips and instructions.

EDIT:
will post pictures when im done.

 

[(*steve*)]

Sorry, I just had the time to look at those resistors again.

I can't figure out what the bands might be. The apparent multiplier stripes don't make any sense.

Maybe someone else can have a go at figuring them out...

 

[AlenZGB]

Gonna desolder them down, measure and take to local electronic shop to see if they have anything similar.

 

[AlenZGB]

Replace bad components, resolder them on board.
5 resistors and 2 transistors B136-600D (one definitely gone bad)
before

after

2 resistor 5W10 ohms, old ones were 2W will that be problem ?

 

[(*steve*)]

Considering that the 2W ones got pretty hot, 5W as a replacement is a very good idea.

That one on the right was almost certainly more than 2W (5W?) so the replacement is appropriate, but check for overheating.

It looks like you've mounted them off the board which is a good thing for cooling.

I wouldn't have thought that 6k8 was the value of the resistor on the right. However it did seem quite discoloured.

 

[jpanhalt]

@Alen,

I just saw this post. We have been corresponding about bad capacitors.

Are you in a place that allows lead solder? If so, get some. Also, I would recommend a decent, temperature-controlled, fine tip soldering iron for replacing typical two-lead and three-lead components.

John

 

[(*steve*)]

So I guess I should ask to see the other side of the board to see what your soldering looks like...

 

[AlenZGB]

@Alen,

I just saw this post. We have been corresponding about bad capacitors.

Are you in a place that allows lead solder? If so, get some. Also, I would recommend a decent, temperature-controlled, fine tip soldering iron for replacing typical two-lead and three-lead components.

John

I have been using 60/40 Tin/lead so far with 2.2 flux inside. Hope thats good enough.

As far as soldering station goes i have this one
description is on english
http://www.chipoteka.hr/artikl/9978/lemna-stanica-sa-temp-kontrolom-zd-937

i know its not weller but for now i cant afford one
but for now i think this one isnt that bad

Considering that the 2W ones got pretty hot, 5W as a replacement is a very good idea.

That one on the right was almost certainly more than 2W (5W?) so the replacement is appropriate, but check for overheating.

It looks like you've mounted them off the board which is a good thing for cooling.

I wouldn't have thought that 6k8 was the value of the resistor on the right. However it did seem quite discoloured.

I didnt know what to do, but seems to me like a logical choice,so i pick 5W instead od 2W. and i try to lift them up from the board as much as i can but im limited with space because board is mounted on the back side and pretty close is air pump so that is as far is i can go.

Yea it was 6K8 even with probs on. colors cant be red from photos sometimes.

So I guess I should ask to see the other side of the board to see what your soldering looks like...

Sorry about that, was on tight time. Im not now at home, ill come tomorrow then ill post some pictures from back side.