Tefal GV8962 Pro Express steam iron - no power
 

Hi,
I am trying to save a donor steam iron with no power supply.
Dismantled and initial visual check on the power supply PCB - there is no fuse anywhere, and resistor is quite obviously burnt. Can't really read to color code, guessing it could be 100ohm (brown, black, brown, gold) or 180ohm (brown, grey, brown, gold).

Replaced the burnt resistor with a trial 5W 100ohm resistor for quick test, power on, and it immediately blown a 100nF 50V capacitor nearby.

Suspect a short circuit somewhere, I try to checked a few more obvious components before seeking help from here:
1) Transistor SCR(labelled on the board), marking is X0602 - do not know how to test.
2) Transistor TR2(labelled on the board), marking is Z0103 - do not know how to test.
3) Bridge rectifier - do not see a single component with 4 leads as advised, but found the 4 diodes labelled D1-D4. D1,D2 and D4 are SMD at the circuit side and measured ~703ohm one direction, infinite reversed. D3 is on the components side, measured ~ 31ohm both direction.

Please help, thank you.

Re: Tefal GV8962 Pro Express steam iron - no power
 

Start with taking of the blown and bad parts. Make pictures as you go along, so you know where what went and which direction these components are facing, because this is critical.
Also take D3 out and measure it out of circuit. There is a dead short in the hot (AC input) section of the PSU. If something measures funny in circuit, take the component out and measure it again out of circuit.
What is printed on U1?

Re: Tefal GV8962 Pro Express steam iron - no power
 

Marking on U1 - LNK304PN.

Marking on D3 - 8G 28Y. I google but don't seems to find any info this part. This should be a regular diode measuring ~700ohm like the rests of D1,2,4?

Re: Tefal GV8962 Pro Express steam iron - no power
 

u1 = offline switcher ic no problem to get. did you take d3 out of circuit and check it if it is indeed shorted? those markings on the diode do not tell me anything, I think there is more hidden underneath. That diode should have a voltage drop of 0.5 to 0.7V or 500 to 700 ohms and it should read that only one way. replace the blown capacitor with same or better specs.

Re: Tefal GV8962 Pro Express steam iron - no power
 

I trace out the board layout for the SMPS Buck converter section:
One end of R4 is connected to Line, it looks to be used as fusible resistor so it will be low Ohms resistor, another end of R4 is connected to rectifiers D1 which is connected in series with D2, the output of the rectifier is filter by filter cap C5 to give DC Voltage to run SMPS IC U1.
You need to check and see if the internal power MOSFET inside U1 is OK or not, also check D1 and D2 RESISTANCE in both directions.

If SMPC IC input shorted to output (shorted internal MOSFET), it will dump high Voltage (over 300VDC) to C2 and blow up the cap.

Here is the sample circuit of the SMPS Buck converter.
https://ar.pinterest.com/pin/621848661029499082/

Re: Tefal GV8962 Pro Express steam iron - no power
 

Took off 1 side, and it seems to be good with 570ohm one way and open the other. So this diode is 1N4007?

Re: Tefal GV8962 Pro Express steam iron - no power
 

D1 & D2 both read ~703ohm one direction. Since D3 now reads 570 off circuit, so mostly likely is this LNK304 shorted? How to test to confirm?

Also, I have no access to the PCB right now, I can't find R4 in those pics that I sent.. Can you point it out please? Thank you.

**edit: do you meant R1 in the picture?

Re: Tefal GV8962 Pro Express steam iron - no power
 

Sorry, my typo, it's R1.
You can test the internal MOSFET for shorts by checking the resistance between S (Source) and D (Drain) pin of the SMPS IC, look at the spec heet of the IC I attached in my post #5.

Re: Tefal GV8962 Pro Express steam iron - no power
 

The resistance between D-pin and the 4 S-pins are all 30 ohm. So this means U1 is good and not the cause of the short circuit?

Re: Tefal GV8962 Pro Express steam iron - no power
 

Nope, It is bad.

Re: Tefal GV8962 Pro Express steam iron - no power
 

take u1 out and measure d3 again in circuit

Re: Tefal GV8962 Pro Express steam iron - no power
 

I gotten a new LNK304PN, and it reads 5M+ ohm between Drain Pin and each of the 4 Source Pin.
I removed the shorted chip (it reads 28ohm between Drain and Source), and soldered back D3, and it still reads 30 both directions.. I think the circuit is shorted somewhere because it already measured 30 between the 2 solder points before D3 is re-inserted.

Re: Tefal GV8962 Pro Express steam iron - no power
 

is there a piece missing off TR2?

Re: Tefal GV8962 Pro Express steam iron - no power
 

D3 will not be a 1n4007 diode, it will be a ultra fast switching diode and likely 1Amp, 1kv maybe a UF4007

Re: Tefal GV8962 Pro Express steam iron - no power
 

I think other component (the 50v filter cap was blown due to high Voltage dump) that are connected to the buck converter are damaged when you power it up with bad IC, you were dumping over 300VDC into the low Voltage circuit.

Re: Tefal GV8962 Pro Express steam iron - no power
 

...and that 5w 100ohm resistor replacement that couldnt blow...

Re: Tefal GV8962 Pro Express steam iron - no power
 

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.

Re: Tefal GV8962 Pro Express steam iron - no power
 

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.

Re: Tefal GV8962 Pro Express steam iron - no power
 

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

Re: Tefal GV8962 Pro Express steam iron - no power
 

Yes, the initial state when I opened up the steam iron, this cap was ok visually, and R1 was burnt. When I replace R1 with a 5W resistor, this cap blown while the 5W resistor survived..

Re: Tefal GV8962 Pro Express steam iron - no power
 

thats good, because the 1n4007 is too slow.

Re: Tefal GV8962 Pro Express steam iron - no power
 

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

Re: Tefal GV8962 Pro Express steam iron - no power
 

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

Re: Tefal GV8962 Pro Express steam iron - no power
 

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).

Re: Tefal GV8962 Pro Express steam iron - no power
 

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

Re: Tefal GV8962 Pro Express steam iron - no power
 

Yes, valuable lesson learnt, thank you.

Re: Tefal GV8962 Pro Express steam iron - no power
 

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

Re: Tefal GV8962 Pro Express steam iron - no power
 

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?

Re: Tefal GV8962 Pro Express steam iron - no power
 

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?

Re: Tefal GV8962 Pro Express steam iron - no power
 

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.

Re: Tefal GV8962 Pro Express steam iron - no power
 

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?

Re: Tefal GV8962 Pro Express steam iron - no power
 

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

Re: Tefal GV8962 Pro Express steam iron - no power
 

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?
-

Re: Tefal GV8962 Pro Express steam iron - no power
 

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

Re: Tefal GV8962 Pro Express steam iron - no power
 

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

Re: Tefal GV8962 Pro Express steam iron - no power
 

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.

Re: Tefal GV8962 Pro Express steam iron - no power
 

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.

Re: Tefal GV8962 Pro Express steam iron - no power
 

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...

Re: Tefal GV8962 Pro Express steam iron - no power
 

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?

Re: Tefal GV8962 Pro Express steam iron - no power
 

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