Samsung WD80N645OOW died mid-cycle

[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]

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]

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]

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]

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]

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.

[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]

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.

[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 .

[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.

[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.

[mrsith]

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

[CapLeaker]

Hope it stays working now.