Weller PU81 bad transformer?

[rtstorm]

Hello, my Weller PU81 wont started today

I check and see that fuse burned (0.5A/240V), replaced it and same thing happened.

I try widouth soldering iron attached - no help.

I disassamble PSU and check transformer with ohm resistance. Primary is 15.7 Ohm and secondary is 0.03 Ohm. I think it is gone bad, am i right?

[eccerr0r]

Re: Weller PU81 bad transformer?

You should use the dim bulb tester to test shorts so you won't be eating fuses. Does it still burn fuses/dim bulb lamp glow very brightly if the secondary is disconnected from the rest of the circuit?

[redwire]

Re: Weller PU81 bad transformer?

Found this PU 81 schematic on the web.
I would disconnect the xfmer secondary and use the dim bulb tester (say across on/off switch) to see what happens.

[rtstorm]

Re: Weller PU81 bad transformer?

But if the primary have 15 Ohm and by the Ohm law I=U/R (230V/15 Ohm = 15.3 A) am i right?

So i think the primary should be minimum 500 Ohm so that Fuse (0.5A) can handle it

[budm]

Re: Weller PU81 bad transformer?

You are comparing the DCR of the transformer widing to the impedance of the winding due to fact that AC is applied to the transfOrmer, not DC.

[eccerr0r]

Re: Weller PU81 bad transformer?

That is true, if you're applying 230VDC to the iron, it will blow fuses unlike direct heat solder irons... These low voltage isolated temperature controlled irons require AC for not just the transformer, but temperature control too. Tossing that out just in case...

[rtstorm]

Re: Weller PU81 bad transformer?

yes you are right, i check now with dimm bulb and transformer give 24VAC on secundary. So my problem is in circuit.

Here is the picture of it. I check the big voltage regulatore and it is ok.

[rtstorm]

Re: Weller PU81 bad transformer?

The big one is triac (BTA12-600CW)

[rtstorm]

Re: Weller PU81 bad transformer?

i try to connect Amp meter in series with dimbulb. With Iron i got 0.18A and my iron is heating but wont stop heating. LED is constant on

[cpt.charlie]

Re: Weller PU81 bad transformer?

Check the thermal sensor located in the heating element.

[rtstorm]

Re: Weller PU81 bad transformer?

What do you mean to check thermal sensor, how?

I put the 2A fuse instead 0.5A and now all working ok but i know rhat is not solution

[sam_sam_sam]

Re: Weller PU81 bad transformer?

Is that a .5 amp fast acting fuse or is this a .5 amp slow blow fuse this will make a difference recheck the original fuse to see which type it is

Dose this iron glow red while it is on and is the led flashing if this is the case you have a problem

Dose the led flash slowly or dose it flash fast and dose not glow red it might be alright if you have a way to check the iron temperature this would something to check

I hope this helps

[rtstorm]

Re: Weller PU81 bad transformer?

hmm you could be right. I throw away original fuse but it might be slow act - i did not think about this. i will try to put 0.5A Slow act fuse and see what happen.

Thank you for that

[vinceroger69]

Re: Weller PU81 bad transformer?

These two files are part of the schematic that may help

[sam_sam_sam]

Re: Weller PU81 bad transformer?

If you can not find a .5 amp slow blow fuse you could use a 1.25 to 1.5 fast acting you might even get by using a 1 amps fuse but you would have to try it

[cpt.charlie]

Re: Weller PU81 bad transformer?

What do you mean to check thermal sensor, how?

I put the 2A fuse instead 0.5A and now all working ok but i know rhat is not solution

If your iron doesn't stop heating, maybe you have a bad thermocouple (open).

[zx8401]

Re: Weller PU81 bad transformer?

Check D2 and D7, one may be shorted.

[budm]

Re: Weller PU81 bad transformer?

So the TRIAC is not shorted out or has leakage resistance?

[rtstorm]

Re: Weller PU81 bad transformer?

No, triac is ok

[budm]

Re: Weller PU81 bad transformer?

So if you lift one end of Gate resistor R4 the iron will no longer gets hot for sure?