Post B8VMTIIDffMUPNQggi by emma@raru.re
(DIR) More posts by emma@raru.re
(DIR) Post #B8V5vCurYZZQcWEFWq by emma@raru.re
0 likes, 0 repeats
pov your newly bought used vintage sewing machine just blew itself up (probably) 'cause some dust settled in a very unfortunate location on the circuit board
(DIR) Post #B8V65QvqIj48z9Yz4q by emma@raru.re
0 likes, 0 repeats
Seems like this is "common" since this lovely blog post (https://www.bionoren.com/blog/2024/08/viking-husqvarna-optima-190-circuit-board/) had the same issue and also very kindly posted images of the replacement board they acquired (which don't render on firefox for some reason)
(DIR) Post #B8V6IWuVNuTLI9BNj6 by emma@raru.re
0 likes, 0 repeats
Now does anyone perhaps know someone in Hamburg who might have a spare 390 Ω 5% resistor on short notice?#boostwelcome
(DIR) Post #B8VAIhJf60gfNhHj3A by emma@raru.re
0 likes, 0 repeats
I just realized why all these wires are needed, this is an etched single layer pcb, so they are for crossing traces :blobcatNotLikeThisCry: At least desoldering the resistor was really easy, almost like this might've been assembled by hand
(DIR) Post #B8VIAqJ4aK9Ka6m6T2 by emma@raru.re
0 likes, 0 repeats
@divVerent First of all, thank you already for all the helpful notes. I've attached some better pictures of my board if you can/want to have another look.I'll have to see if I can borrow a multimeter, or get one somehow (should really be something I buy one of these days)I really don't think it's the IC, even in the blog it looks fine. Yes, it's in the splash zone, but at least on mine, the housing is pristine, so I'm gonna assume it's fine.Those radial capacitors also look fine to me, not sure what their usual failure mode is but the housing seems intact, and there's no residue or anything around them.What does worry me is those two boxy 250V 0.1µF metal-paper capacitors. The left one kinda looks fine besides some probably age-related cracks in the plastic housing... But the right one (now?) has a bulge in the housing right across from the offending resistor.Also my board seems to be wired slightly differently to the one on the blog, and I'm missing the 0.01µF capacitor, which looks like somebody has previously de-soldered it badly... So I'm wondering if it makes sense to replace that one also...What is kind of worrying me is that whatever it was, didn't even blow up while I was using it. I was stepped away for a moment to iron something and then I just hear the motor turning on and shortly after a lot of horrible smelling smoke...
(DIR) Post #B8VMTIIDffMUPNQggi by emma@raru.re
0 likes, 0 repeats
@divVerent Also I had a look, and the two-pin plug goes to the lamp, so yeah it's pretty much just a switched live wire. The 5-pin is going into the motor, and the other soldered wires are going to the buttons at the front.Something maybe worth mentioning, the motor was actually quite warm when I unplugged the machine and opened it up...Anyhow, I'm gonna order replacements for the resistor, and those three capacitors, and see if I can get a multimeter somewhere tomorrow
(DIR) Post #B8WUbtErBWzy6MQUc4 by emma@raru.re
0 likes, 0 repeats
@divVerent Thank you once more for your insight. I gotta remember that trace overlay trick, very useful ^^Replacements for the 0.1µF capacitors are ordered. And I will definitely give the other capacitors a check before turning anything back on.I also had a bit of a read on those 0.1µF capacitors, and they are supposed to be "failure resistant." It seems shorts should "self extinguish" with it instead loosing a bit of capacitance for every short. With the age they probably are, it could well be that my earlier use yesterday might've given the right one its last push to short out.The motor actually is a 220-240 V 50-60Hz AC motor, with a little circuit board layered into it. From the front there's a switch for "halving" the total motor speed, and another to enable some digital magic that always finishes a stitch with the needle all the way up or down. I suppose those features probably require all the extra wires going to the motor.The dark spot on the IC looks to just be soot (see picture)
(DIR) Post #B8XJ3IoxAsGUyDZiIy by emma@raru.re
0 likes, 0 repeats
@divVerent I got a multimeter and honestly I'm a little baffled... The blue caps all read what it says on the tin, the diode "diodes" just fine. Even the decroded yellow capacitors seem mostly fine, albeit the left one reads about 0.14µF and the right one 0.11µF but I have no idea if that's within tolerance or what else.Well parts are ordered anyway, I'm gonna go ahead an make the planned swaps. Perhaps it was a freak power imbalance from the grid, and all just works fine after all.If worst comes to, one of the ICs or even the motor is to blame after all, I'm gonna have to see if I can find a donor anyway... Or just scrap the thing, sad as it would be.I will report back once I have the parts back in place :bunPeek: Either outcome, thank you so, so much for your very exhaustive and detailed help
(DIR) Post #B8bHHI2U9IXN7alasq by emma@raru.re
0 likes, 0 repeats
@divVerent Last of the parts arrived today (thank you eBay resellers, RIP to ordering directly from AliExpress in Germany) and I went and swapped them in.Seems to have bern a resounding success. Stitches just like before in all direction and speeds, no suspicious smell and the motor seems cold to the touch after I left it turned on for about 15 minutes. I'm gonna keep close watch for a little longer while I'm using it, but I think it's fixed. Thank you so much for your guidance I certainly learned a bunch.On another note, it really seems that cracked capacitor is very dead and more than likely at fault somehow. Compared to the other one (I also replaced) it has this brown mark running across visible from the bottom that just can't spell anything good.Last thing I want to ask, I did look for motor replacements, but anything I found was out of stock and also wildly expensive. I made photos of the two brushes on the main motor, and it looks to me they're in decent condition all things considering, am I wrong?