Tefal GV8962 Pro Express steam iron - no power

[beetle1303]

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.

[CapLeaker]

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?

[beetle1303]

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?

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?

[CapLeaker]

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.

[budm]

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/

[beetle1303]

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.

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

[beetle1303]

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/

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?

[budm]

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.

[beetle1303]

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.

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?

[budm]

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?

Nope, It is bad.

[CapLeaker]

Re: Tefal GV8962 Pro Express steam iron - no power

take u1 out and measure d3 again in circuit

[beetle1303]

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.

[CapLeaker]

Re: Tefal GV8962 Pro Express steam iron - no power

is there a piece missing off TR2?

[R_J]

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

[budm]

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.

[CapLeaker]

Re: Tefal GV8962 Pro Express steam iron - no power

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

[beetle1303]

Re: Tefal GV8962 Pro Express steam iron - no power

is there a piece missing off TR2?

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.

[beetle1303]

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

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.

[beetle1303]

Re: Tefal GV8962 Pro Express steam iron - no power

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

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

[beetle1303]

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.

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..