Tefal GV8962 Pro Express steam iron - no power

[beetle1303]

Originally Posted by CapLeaker

I think C7 may be shorted too. Take it out and remeasure it out of circuit.

OK, I think it will mostly likely be a destructive removal..

[beetle1303]

Originally Posted by budm

Now check the resistance between GND and VCC pins of the IC's.

Hmm.. I missed out the most devastating part when remove U2 without the right tools - the black material cracked into pieces when I tried hard to remove it with a soldering iron and a tweezer...

So, ya, can't do any test on U2

[budm]

I am talking about the two IC's that you found the spec sheet to get the VVC pins, check the resistance of those VCC pins.
BTW, since you cannot do SMD repair so it is a moot point to keep trying to fix the board.

[beetle1303]

Originally Posted by CapLeaker

I think C7 may be shorted too. Take it out and remeasure it out of circuit.

I took out C7 - off circuit fluctuated between 3.8 - 14 uF, probably the contact points are somewhat damaged... The resistance between the 2 C7 pads reads 20.8 ohm, same reading with the C7 in circuit.

[beetle1303]

Originally Posted by budm

I am talking about the two IC's that you found the spec sheet to get the VVC pins, check the resistance of those VCC pins.
BTW, since you cannot do SMD repair so it is a moot point to keep trying to fix the board.

The resistance of those 2 ICs are both 20.8 ohm. After removed C7, same reading.

Yes, indeed it will be purely academic from now on. And if there is any further fault finding worthwhile, it can only be done with SMD removal, and not restoring as I am not equipped and not capable.

At this juncture, I want to thank you both, BUDM and CapLeaker, for spending time coaching me. It's been a pleasure learning under your coaching.

Thank you very much.

[budm]

Originally Posted by beetle1303

The resistance of those 2 ICs are both 20.8 ohm. After removed C7, same reading.

Yes, indeed it will be purely academic from now on. And if there is any further fault finding worthwhile, it can only be done with SMD removal, and not restoring as I am not equipped and not capable.

At this juncture, I want to thank you both, BUDM and CapLeaker, for spending time coaching me. It's been a pleasure learning under your coaching.

Thank you very much.

So pin1 of U2 is the Output pin for feeding VCC for the IC's.
You can try removing C7 first to see if the resistance will go up or not, there are also other filter caps connected to this VCC line that have to be checked, worst case will be that the IC's are damaged.

[beetle1303]

Originally Posted by budm

So pin1 of U2 is the Output pin for feeding VCC for the IC's.
You can try removing C7 first to see if the resistance will go up or not, there are also other filter caps connected to this VCC line that have to be checked, worst case will be that the IC's are damaged.

I have already removed C7 and the resistance remains unchanged at 20.8Vdc. I have also attempted to trace and measure all the caps an resistors leading to the Vcc of the 2 ICs. Not surprisingly, I do not know what I was doing... But I feel the resistance pretty much measured 20.8Vdc in most places along the trace.

I reckon that this would not go very far to determining what else is faulty beside the now apparent U2 being blown opened. But suffice to say replacing the R1 with a 5W 100 ohm was a MAJOR MISTAKE!! Nonetheless, it has been very educational, and I want to thank you (and CapLeaker) once again for patiently guiding me alone this learning journey.

Thank you.

[budm]

Originally Posted by beetle1303

I have already removed C7 and the resistance remains unchanged at 20.8Vdc. I have also attempted to trace and measure all the caps an resistors leading to the Vcc of the 2 ICs. Not surprisingly, I do not know what I was doing... But I feel the resistance pretty much measured 20.8Vdc in most places along the trace.

I reckon that this would not go very far to determining what else is faulty beside the now apparent U2 being blown opened. But suffice to say replacing the R1 with a 5W 100 ohm was a MAJOR MISTAKE!! Nonetheless, it has been very educational, and I want to thank you (and CapLeaker) once again for patiently guiding me alone this learning journey.

Thank you.

At least you gin the knowledge. One of the weak point of Buck converter is that when the pass device (I.E. MOSFET) shorted out, the input Voltage will be dumped into the load and can cause lots of damaged, they should at least put crowbar and a fuse on the output.