Samsung WD80N645OOW died mid-cycle

[CapLeaker]

Hope it stays working now.

[mrsith]

Quick wash finished with no issues. Thanks so much everyone for help, I learned a lot during the whole process!

[mrsith]

Trace was bad. Looked alright to eye, but didn't conduct fromain fuse to that NTC resistor. Had to take the relay out to make sure it's actually the same trace lol. Made a jumper, found a similar diode on one of scrap TV mainboards I had in cupboard (was a bit bigger, marked T4 P with P being rotated), put it together and the machine turns on again. Need to assemble. It back, connect water and drain and see if it manages to finish a program.

[CapLeaker]

That could be it, maybe I have burnt the trace coming from fuse to the smaller rectifier. I'll take out the fuse tomorrow and check the traces around it. I was quite gentle with soldering iron, but heated the solder quite long to make sure it flows where it needs to. Maybe that was too long.
There are similar relays on the board, coil resistance looks similar. That main relay only activates when the power button is touched, so I guess even if something was wrong there, I should still be getting 5v and 12v to power to control panel.

just place a jumper wire for now.

[petehall347]

Edit: also found a tiny T4 marked diode, just next to the relay (looks like it's connected to the relays coil), which is open, doesn't conduct anything any way.

flyback diode . relay will switch on without it .but if its open the relay drive circuit might be damaged .

[mrsith]

That could be it, maybe I have burnt the trace coming from fuse to the smaller rectifier. I'll take out the fuse tomorrow and check the traces around it. I was quite gentle with soldering iron, but heated the solder quite long to make sure it flows where it needs to. Maybe that was too long.
There are similar relays on the board, coil resistance looks similar. That main relay only activates when the power button is touched, so I guess even if something was wrong there, I should still be getting 5v and 12v to power to control panel.

[sam_sam_sam]

Sometimes you might not get a resistance on some relay coil if it has more than one of the same type of relay check the coil on each one to make sure that it is really open
One note if this is a double sided board make sure that you heat the soldering joint completely but not too the point that you burn the board or you make the trace from pealing off the board

[mrsith]

It's marked on pcb thankfully.

Would I get any dc reading at all if only one ac terminal was connected to a rectifier? Maybe I actually shoved my probes right there, just only one pin was getting ac power so the reading was 0? That'd explain no continuity between rectifier and ac L input, and pretty much everything else that's happening with the board.
I'm afraid I'll have to take the relay out anyway, just to see the traces underneath.

[CapLeaker]

Hopefully you can figure out which way the diode was. If the old diode is bad, just put something like a 1n4148 in there. If you don’t it will damage the coil driver.

[mrsith]

I'll continue with that relay, like I said I got excited too quickly and thought it's a different pin that conducts the N line. Relay seems good.

I've been measuring that diode out of circuit. Seen 152ohms both ways in circuit, so I was scraping the silicone around the relay off to have a better view on that diode, and it fell out with the silicone. Soldering pads healthy at least.

One of the rectifier's legs connects straight to the N ac line, trying to figure out which way the positive line goes there. Doesn't seem to conduct against L ac input. There's a NTC resistor measuring 25ohm, I can see trace from it coming under the main relay, there's a trace coming on another side that connects to the main fuse, but there's no continuity there.

[CapLeaker]

I guess we have to wait for parts now? Or can you continue with the old relay?
what is the diode saying now out of circuit?

[mrsith]

There's 152 ohms there on the coil, same in the spot where diode was. There is a slight chance that I damaged it when pushing probes through the resin though. Ordered a replacement.

Gonna try measuring ac input on the rectifier again, it's difficult to stick probes there.

[CapLeaker]

That t4 diode is probably in parallel with the relay coil and is similar to a 1n4148 small signal diode. It is there as a high voltage protection for the coil drive when the relay is triggered. It should show up almost as a short, since you measure through the coil of the relay.
edit: so if you measure across the coil and it is open with the diode, that the relay is fuxed.

The voltage at the rectifier is not normal. So you probably have a weird AC voltage on the bridge rectifier input, or the bridge rectifier is bad.

[mrsith]

Well I've made a mistake, it's the other pin of that relay that's supplying the N ac line. And it's normally closed so that relay has to be switched on first. This means there's whole another route of power here.

Starting with DF06S rectifier, I'm getting dc output of circa 50 volts, raising steadily (~10v at a time) to circa 110v,then drops again to 50s and raises again. Is that normal?

Edit: also found a tiny T4 marked diode, just next to the relay (looks like it's connected to the relays coil), which is open, doesn't conduct anything any way.

[CapLeaker]

I just wanted to say that there is nothing much in between the rectifier and the power cord, but you are in the right track. The relay could have burnt contacts not letting enough juice go through.

[mrsith]

Think I've found the problem. The N line goes through one of the main relay pins - confirmed via continuity against plug's N pin, relay's leg and the bridge rectifier leg. When I measure A voltage with CN7 L pin L and the relay plug (there's enough space to shove a probe between the plug and the relay when it's connected), I have stable 245v, but when I take the measurement using the relay leg on the other side of the board - which has continuity against that plug - I have same jumping voltage as measured on rectifier itself.

Gonna try reflowing that relay, if nothing changes I'll take it out and open it to see what's happening inside.

[CapLeaker]

Make a picture and draw or circle on it.

[mrsith]

I've been checking voltage on mainboard connectors, used the CN1 live line for plus (it's the main ac input for the board) and RY7 negative for minus (seen it has continuity against N line of the mains plug), got stable 245v there. I think everything goes through filter before it reaches the boards?

Spade terminals (the ones I'm aware of and I can somehow access) look brand new.

[stj]

no stable ac on a primary rectifier - check for loose spade terminals on everything upstream - seen it a lot on older stuff but never anything this new.
but worth a look, also check the mains filter - i'm sure it has one.

[mrsith]

It's str-W6053s.

I'm still trying to figure out why this all might've happened. With drain/circulation pumps, does polarity matter? Wouldn't think so as it's AC, but I remember the pump had pins marked L/N, I didn't remember which was which so just put orange wire to L, blue to N, guided by common sense. The machine acts the same even without pumps disconnected though.

Also why am I not getting stable AC on the bridge rectifier? It's the 1st component after the fuse, and both ac and dc measures taken from it seem wrong. Dc volts looked kinda similar to what I could read on PWM Vcc pin.