Tefal GV8962 Pro Express steam iron - no power

[CapLeaker]

Originally Posted by beetle1303

I bought a 1N4007 as replacement but have not soldered it in. I used back the original D3 diode, which was reading 576 off circuit in direction only.

thats good, because the 1n4007 is too slow.

[beetle1303]

Now about D3, what other bad components would cause the 2 solder points to read, with or without the D3, 30ohm both ways?

[CapLeaker]

Originally Posted by beetle1303

Sorry, I don't get what you meant..
TR2 reads 846 ohm one way between left and center pins, 793 reversed direction, and open in all other combinations.

Your pic #1 bottom right. TR2 looks like it is damaged a little on the top. What is printed on TR2?

[CapLeaker]

Originally Posted by beetle1303

Yes, using this 5W 100ohm is bad idea.. I have gotten a 2W 100ohm to try out later.

Yes, that was a very bad idea actually. In this case this resistor is a flame proof (green colour) resistor that is used a fusible resistor. Now you putting is there a 5W resistor, I am not sure if that is actually the only damage it did (blowing that 50V cap).

[beetle1303]

Originally Posted by CapLeaker

Your pic #1 bottom right. TR2 looks like it is damaged a little on the top. What is printed on TR2?

Z0103MA. There is some think there but don't seems to be cracked...

[beetle1303]

Originally Posted by CapLeaker

Yes, that was a very bad idea actually. In this case this resistor is a flame proof (green colour) resistor that is used a fusible resistor. Now you putting is there a 5W resistor, I am not sure if that is actually the only damage it did (blowing that 50V cap).

Yes, valuable lesson learnt, thank you.

[budm]

The value of that fusible resistor will be likely be <10 Ohms.
https://ar.pinterest.com/pin/621848661029499082/

[beetle1303]

Originally Posted by budm

The value of that fusible resistor will be likely be <10 Ohms.
https://ar.pinterest.com/pin/621848661029499082/

From this picture view - it seems like a 4-band resistor: Brown, ?, Brown, Gold. Brown, Black, Black, Gold gives 10 ohm, unless it's Black, Grey, Black, Gold to give 8 ohm?

[beetle1303]

I moved one of the 2 relays, and here's a findings:
1) The pins (red arrow) reads 1569 ohm
2) I applied 12V, both directions, to these pins thinking it should click, but it does not.
3) The in-circuit relay also reads 1569 ohm, and also does not click when applied 12v to the coil pins.

Is this normal?


Next I removed the inductor L2:
1) I don't have DMM that read inductance, but resistance reads 1.8 ohm.
2) With L2 moved, D3 now reads correctly at 579 ohm in one direction only.

Does this means L2 is bad and shorted?

[CapLeaker]

the first 2 pictures show a 24v relay not a 12v, the 3rd pic the inductor. The inductor should be ok showing 1.8 Ohms.

[budm]

The buck converter looks to be set up for 24V output, you can verify that by checking the value of the feedback resistor network , that is why the blown up C2 is rated at 50V, twice the operating Voltage.
I would not pull the relay out, you should concentrate on what component are connected to + lead of that filter cap C2. if you check the resistance between the two legs of the filter cap c2 solder pads, what do you get, 30 Ohms?

[budm]

I trace out the relay driver, the buck converter is set to 24V for the relay coils.
Transistor T2 drives the relay REL1

[beetle1303]

Originally Posted by CapLeaker

the first 2 pictures show a 24v relay not a 12v, the 3rd pic the inductor. The inductor should be ok showing 1.8 Ohms.

Arh.. silly me.. Yes, I applied 18v and it clicks, both off and in-circuit.

With Inductor L2 removed, D3 measured correctly at 579 one way. When removed, it measured 30. Seems to by-passed to a shorted circuit somewhere?
-

[beetle1303]

Originally Posted by budm

The buck converter looks to be set up for 24V output, you can verify that by checking the value of the feedback resistor network , that is why the blown up C2 is rated at 50V, twice the operating Voltage.
I would not pull the relay out, you should concentrate on what component are connected to + lead of that filter cap C2. if you check the resistance between the two legs of the filter cap c2 solder pads, what do you get, 30 Ohms?

Yes, both relays clicked when I applied 18v into them. And yes, the 2 solder pads of C2 reads 30 ohm.

[R_J]

Why don't you remove C2 and check it out of circuit, or remove it and check the solder pads to find out what is reading 30Ω

[budm]

D3 is basically in parallel with the load through the Low DCR of the Buck inductor, that is why you see 30 Ohms when D3 is measure in the circuit, look at the circuit of the Buck converter then you will understand why.

[budm]

Originally Posted by R_J

Why don't you remove C2 and check it out of circuit, or remove it and check the solder pads to find out what is reading 30Ω

I would have thought he had removed that blown up cap already since it is blown up, if not then I do not understand why it is not removed.

[beetle1303]

Originally Posted by R_J

Why don't you remove C2 and check it out of circuit, or remove it and check the solder pads to find out what is reading 30Ω

C2 already removed when it "exploded" on powered up.. but it still ready 89uF off circuit. The 2 solder pads between them ready 30ohm. I traced the +ve pad along the path to R31 and R31 read 120k ohm.

Not sure where to trace further...

[beetle1303]

I decided to restore all the good and new components back into the PCB and do a basic continuity check - new 2W 100ohm R1 resistor, new 50v 100uF C2 capacitor, new U1 LNK304, and the original L2 inductor.

All pretty much the same, except now D3 now reads 579 in circuit.

I connect a 40W incandescent bulb between the Live wire of the incoming power. Power on - the incandescent bulb do not light up at all, the I measure to incoming voltage to the PCB - 243V.

But pressing the power button of the device - nothing happened, nothing blown, no led light.. Something component(s) blown opened?

[budm]

So now you are saying the resistance on C2 no longer show 30 Ohms?
Do you have 24Vdc on C2?
You also need to find out if you also have low Voltages to runs those IC or not