LNK624DG blown on Motor CTLR 421297NAP in Fisher & Paykel Washer

[KPO967]

Hello all,

From the subject above, I have a blown SMPS controller LNK624DG on motor controller 421297NAP in Fisher & Paykel WA70T60GW1

The blown chip I had, could only read "LNK*****G"  as the top blew off.

This thread:   https://forums.whirlpool.net.au/archive/9j58w223   gave me access to images of the same motor controller board where the damage to the same chip revealed more of the part number to determine it is LNK624DG.

When I order and replace this, what other components should I be checking?  Or replacing outright?

[xavier60]

I think you are lucky with that one. The IC doesn't appear to have violently blown, blackening the surrounding area and destroying many other components including the micro-controller.
First check the state of the micro-controller by taking a resistance reading between the 2 outer pads of the group of 3 large pads near the display connector. It should be about 170Ω.
Also check the transformer's primary resistance, it should be close to 10Ω.

[KPO967]

172 OHM for microcontroller test and 10 OHM for Primary winding.

Just out of curiosity, I did have LNK626DG and installed it which is a higher power version (on the same datasheet as LNK624DG)

When I powered up, the power button still didn't turn on the system, and there was a faint, high pitched resonance from the transformer.  Also occasionally it would faintly click at even intervals

I ordered the correct part today, to install tomorrow, however I am afraid the same situation would arise.

Any thoughts please?

[xavier60]

I always replace the IC with an LNK626DG. It's common for one or more of the IGBT Gate driver ICs to also fail, loading down the 15V rail.
I sometimes supply the 5V and 15V rails from a bench supply, then check which driver ICs are getting hot.
I never test a just repaired board directly on mains. I use reduced voltage from a variac and/or a series lamp for current limiting. This is to minimize further damage in case a problem has been missed.
A good board will wake up and start beeping on 30VDC.

[xavier60]

Pin 4 of the L6392 driver ICs is   Vcc  and are all tied the 15V switched supply. I got a reading of 47K to ground on one of my spare boards.
The larger than usual SMD transistor near the buzzer is the 15V switch.

[KPO967]

Thankyou for your help xavier60!

L6392 pin 4 resistance to ground is 55K for all 4 ICs.

The 4 diodes around the transformer:

3 Have one-way voltage drop measurement of 0.461V however the 4th diode pictured has 0.111V BOTH WAYS - Is this indicative of replacement requirement?

[xavier60]

Thankyou for your help xavier60!

L6392 pin 4 resistance to ground is 55K for all 4 ICs.

The 4 diodes around the transformer:

3 Have one-way voltage drop measurement of 0.461V however the 4th diode pictured has 0.111V BOTH WAYS - Is this indicative of replacement requirement? (Attachment Link)

That's the 5V rectifier. In circuit it will have the 172Ω across it. It's a Shottky diode and measures 0.185V on my Fluke 87V, out of circuit or with the transformer removed.
Removing the transformer can be difficult. A desoldering station should be used to avoid PCB damage.
Do you have the necessary equipment to power the  5V and 15V rails?

[KPO967]

Haha, I was just about to post that when I removed the schottky from the circuit, it measured correctly.

I may be able to muster up a 15v and 5v power supplies..

When It is on AC, the 5v rail fluctuates btwn 3.5~4v and the 15v rail fluctuates btwn 11ish~13ishv in time with the transformer resonance (it's kind of pulsing at regular intervals)

When I rangle together the power supplies, what would I be looking for?

[xavier60]

5V can be applied to C251 and 15V to C245. The print can be confusing so double check that the polarity is correct and the proper voltages are applied to the respective capacitors. Notice that the capacitors have different voltage ratings.
If the board doesn't have a serious fault, it will wake up and make a burst of quick beeps.
The 5V rail should draw 90mA , 25mA for the 15V.
12V is also Ok for the 15V rail.
 

[KPO967]

Ah, Awesome!, I have plenty of 12's.

When you mentioned: "The larger than usual SMD transistor near the buzzer is the 15V switch." I cannot find details online from the markings to grab a datasheet nor guide for testing if it's ok,

[KPO967]

I applied 12v & 5v to the caps, and the board beeped 5 times rapidly

[xavier60]

I applied 12v & 5v to the caps, and the board beeped 5 times rapidly

What is the current draw? You can put 1Ω resistors in series with your power supplies to measure the voltage drops.

The 15V switch transistor is likely Ok. There should be 12V on the Collector. The Collector should go low when the 5V rail is turned off.

[KPO967]

Current draw was exactly what you quoted, The transistor is behaving as stated.   Hmmm... Would there be an issue with the choke? or the secondary of the transformer?  I can't grasp what else the issue could be...

[KPO967]

Maybe I should replace the caps?

[xavier60]

For such a simple power supply, I have had lots of trouble finding problems. The IC could be damaged by overheating, I only hand solder them.
There is a TVS in series with a diode across the primary, it is the furthest from the IC. See what happens with it removed. The board must be power from low voltage.  Try 30 to 50VDC.

[KPO967]

The TVS removed made no difference, I had the transformer out and measured the coils again, and I got 10 ohm on primary, as I had tested before,  But I get 0ohm on the outer pairs, as described in the image below.  Does this mean there's a short in both secondaries?

[xavier60]

The TVS removed made no difference, I had the transformer out and measured the coils again, and I got 10 ohm on primary, as I had tested before,  But I get 0ohm on the outer pairs, as described in the image below.  Does this mean there's a short in both secondaries?
(Attachment Link)

The secondaries have no reason to be damaged and have a very low resistance. Although the primary resistance seems right, it's still possible to have shorted turns.
Do you know how to do a ring test? Using a 10nF series capacitor driven by a low frequency square wave from a 50Ω source, I got 25KHz damped oscillations.

[shanefnq]

Hello KPO967
I have the same issue with blown LNK624DG chip.  Did you ever complete the repairs to this unit?  If so, can you please advise how you accomplished the repair and which other components you found to be faulty?  Thank you

[neillnz]

Last weekend I went to do our weekly laundry only to find our machine dead.

I found that the LK624DG had a small crater in it.  A search bought me to this forum.

I applied 5V and 15V as suggested above and the controller came alive, emitting beeps as also dscribed above.

There appeared to be no other bad components, diodes still diodes etc.

Today I received some LK626DG from Digikey.  I fitted one of them and applied just 30VAC to the mains input and you beauty, the 5V and 15V appeared along with the beeps.

It is now all reassembled and working just in time for the weekend washing tomorrow.

Thanks team!
 

[xavier60]

Last weekend I went to do our weekly laundry only to find our machine dead.

I found that the LK624DG had a small crater in it.  A search bought me to this forum.

I applied 5V and 15V as suggested above and the controller came alive, emitting beeps as also dscribed above.

There appeared to be no other bad components, diodes still diodes etc.

Today I received some LK626DG from Digikey.  I fitted one of them and applied just 30VAC to the mains input and you beauty, the 5V and 15V appeared along with the beeps.

It is now all reassembled and working just in time for the weekend washing tomorrow.

Thanks team!
 

Well done!
 There a few other common faults like 112. Be sure to ask if you have further problems.

[Bill30]

Hi people, I stumbled across this forum a while ago and it has helped me repair a couple of these modules for friends. I now have one with the 112 fault. Any help would be appreciated. Thanks in advance, Bill.

[xavier60]

The L6392 driver ICs contain an opamp to amplify the signal from their respective 0.1Ω CS resistors. The output of each, pin 6, needs to be biased close to 2.5V. The 112 fault is usually caused by the 1.5K bias resistors drifting. There are 4 of them with each driver IC.
I have not been able to make sense of the marking on these resistors, it slightly resembles "186"
It's best to first power up the board to check the voltage on pin 6 of the driver ICs first. Most boards will wake up at 30VDC.

[Bill30]

Hi xavier60, Thanks for the quick feedback. I think it's 18B not 186?. I will check out the board and advise. Thanks Bill

[beckmanp]

 Great work, the resistor markings are correct as they are EIA-96 markings, of which 18B equals 1.5k.  Found of the 12 1.5k resistors most had drifted to between 1.6k and 1.7k, after replacement, pcb fired up and tested well without dreded code 112. It is interesting that these resistors drift after the repair of a blown lnk624dg, not sure about the relationship between the 2 problems, and will post if any of our repaired pcb's have incurred other problems due to lnk624 failure.
Once again, thanks for your postings.

[beckmanp]

Hey Bill, Xavier60 is a whizard on these problems, my advice if you repair these pcb's with a change of lnk624dg, and have no power up, is that usually the transformer has gone near short circuit, way down from the 10ohms on primary, and on disassembly of transformer the reason becomes self evident. This transformer is unable to be sourced anywhere, and it is possible to rebuild with ee16 parts, wire and tape from aliexpress. Can post info if needed about parts and winding info, but obviously this time you have good luck on your side as you are able to at least get your pcb to fire up and give a code 112.
Good luck, Peter.