Husqvarna Prisma

The Prisma is the model released after the last 2000 series, the 6690. 

I'm not all that fond of computer controlled machines, as you might know, but as a sewing machine mechanic, I need to know how to fix them.

In the USA these are referred to as 7000 series, presumably because the 2000s were called 6000 series in the USA. 

People outside the USA refer to them as Prismas, 900 series, or just 900s. 

The model numbers range from 940 to 990, the latter being top of the range with a lot of embroidery options. 

I had bought a 950 in Brisbane about three years ago. It actually worked okay once I had replaced the power supply capacitor. After the flooding of Feb/Mar 2022 in Brisbane, I put it in storage and didn't switch it on again for quite a while. When I did it didn't work but I still brought it with me to Melbourne. 

It seemed obvious that it was a problem with the main board rather than the power supply board, because the lights still worked, just not everything else. I got around to this several months ago, and decided to ask on the Husqvarna Facebook group. 

My FB friend Hans from Norway immediately suggested contacting Theodor Bastberget, who is an electronics engineer with a special interest in sewing machines. 

Theodor pointed me to his website which is very helpful if you want to learn how to repair your own machine/s.

Fast forward a couple of months and I now have a 940, 950, 960 and 990 and all but one are working now. 

The only one I got in working condition, the 990

If you have one of these machines, the most common problem you will see is from the capacitor having a meltdown. If I see a Rifa capacitor in the power circuitry, I always change it. Replacements are very cheap and available at a local electronics store, and not changing it can have frightening consequences. 

Staying with the power supply, the second thing to go wrong is the diodes. There are eight of these, and when one of them fails, it often destroys some of the copper and burns a hole through the board! Theodor has a picture on his website, but the picture below shows that this one has also had this problem. 

So, remove the power supply as a unit. Four posi screws at the bottom (avoid using a phillips, it wrecks the screw), one of them with a rubber buffer surrounding it. Remove the three short screws to get one cover off, then the three long screws. When I did this, I saw the PS board:

Underside of the power supply board

This is the underside, and you can see that someone has already replaced some failed diodes. This failure burned through the board and removed some of the copper. Someone has soldered in some new diodes and replaced the missing copper with wires and solder. 

Here is the top view:

Not the best job I've seen but it seems to work. I have a special Husqvarna power supply checker that were issued to repairers and I know that this is a working PSU. The capacitor has also been replaced:

The original capacitor was a Riva, which are brown, even more brown when they fail. They usually fail quite spectacularly with a bang, a lot of smoke and a smell you aren't likely to forget.

If you know that you have a good PSU but the machine still doesn't work, it's going to be a problem with the main board. If you find that the zig-zag doesn't work, the problem will probably be with the stepper motor or the stepper motor controller. Same with the feed stepper motor. When you switch on the power, you should hear a noise as the stepper motor self-tests. If there's silence, but the lights come on, press on the foot controller. If the motor goes, unplug the two stepper motor plugs and swap them. Turn it on again and if it makes the noise, the stepper motor is the problem. If it doesn't, it's somewhere else on the board. I have found that the board's capacitors are prone to failure. The board I'm working on at the moment was blowing diodes. I removed the capacitors (and the diode) and this fixed everything except for the motor (it's a work in progress). Capacitors can hold a lot of charge, so the recommendation is to turn the machine off a full day before working on it. That might be a bit extreme, but I got zapped recently, so I'd leave it an hour or two at least before working on it.

Current project, capacitors replaced

It's unfortunate that you can't check components when they're on the board, but you can get experienced in removing them, and you only have to remove one side to check. The large capacitor I removed (and replaced with the big blue one) tested as a 38 ohm resistor! No wonder it wasn't working.

Electronic failures don't mean the end: As far as I know the components are available, and so the machines are repairable.

Edit: The main board was fine, but even though it tested as okay with the Husqvarna power supply test tool, it wasn't! Everything worked except the motor, so I assumed it was a board component. Theodor suggested swapping it with a known good one, which I did, and the machine worked perfectly straight away. I was very pleased and now have another good main board, but since I replaced almost every component in the power supply, the problem with it is the next mystery. If it's the secondary windings in the transformer, I'll have to let that die. It's too expensive to rewind one and they're not that uncommon.

Husqvarna 6440

 These are called Vikings in the US and UK and made in Sweden until about 1976.

They have several very common issues. In fact they're so common that it's rare to not find one or all of them wrong with a machine. The ad came up on marketplace, a Husqvarna 6440 for $20. Extraordinary price but here are the issues in order of importance:

1. Broken pattern gear. Without an intact pattern gear you have a very competent straight stitch machine. Very rare to have one with this intact. Replacements are available but quite expensive.

2. Seized mechanically. Husqvarna used a grease not unlike that used by Janome, within sintered bearings which contain quite a lot. It leaks out when the machine isn't used for a long time and hardens to something that resembles glue. All of the old grease needs to be replaced if you want to use your machine.

3. Broken plastic. The cover is plastic and when bits of it disintegrate, you find yourself gluing the covers on. Not a great look, and very inconvenient when you want to work on it.

4. Capacitor. These tend to fail quite dramatically, with smoke and melted plastic. Best to replace them before they get to that stage (0.1uF, 275V, less than a dollar).

I asked the seller about the gear. She replied that it was intact and that someone else was supposed to pick the machine up on Thursday, so I got next in line. I got a message on Friday to say it was mine.

The seller had apparently been a saleswoman and worked for Bernina for two years in the early 70s then was poached by Husqvarna two years later. It's always nice to know the original owner of a machine, especially if she's knowledgeable and has history in the sewing machine industry.

Back to the machine. The last service was in 2010, and she hadn't used it since then. It was as stiff as a board but would move slightly and as she had said, the original gear was 100% intact. Since it's a one owner machine, I wasn't too worried about too much broken plastic from the case. The plastic piece at the front above the dials had been replaced during the last service. I'm assuming that the technician had spilled cleaning fluids on it and replaced with that of an earlier machine (a 6370). The original one would have said Husqvarna 2000, since the model number is at the bottom right.

After her makeover

Yes it looks really good here but it took about eight solid hours of work to free it all up. This post is mainly to tell you what to do and what not to do with these machines.

Solvent for the grease

I use a 50/50 mix of methylated spirits (denatured alcohol in the US) and mineral turpentine. Get yourself a glass jar and apply with a toothbrush. Before you start though, be aware that although this stuff is like magic on dirt and grease, it will also dissolve the surface of this beloved machine, so apply it extremely carefully. I'll also note that this mixture will also dissolve the surface of any older, black sewing machine, so keep it away from surfaces. I put cotton rags all over any part that could get splashed. If you accidentally splash the paint, don't try and rub it off, or you'll immediately remove the paint. Let it dry. 

Methylated spirit is extremely volatile, meaning it evaporates very quickly, so if you leave it out, it will evaporate and you will be left with pure turps, so put a lid on it. It also will absorb water, which you don't want either, as you'd be putting water inside your machine. I work with a young technician who never puts the lid on and always leaves the jar outside in the heat and rain, so we use a heap of methylated spirits at work.

Removing the covers

Here's the back of a 6370 (I didn't take a photo of the 6440 but they're exactly the same) with the cover removed.

The screws holding the cover on are two big ones on the left and right, as well as one holding the side cover to it, and a couple underneath. Don't remove all of screws underneath, two of them will be securing the mounting for the motor. Be extremely gentle removing these: They're self tapping screws holding onto some very brittle plastic. Even being gentle, a few pieces fell off. I secured them back on with araldyte and waited the full 24 hours before reattaching the covers, also done very gently.

The side cover is removed by pulling out the hand wheel (also plastic and susceptible to falling apart), unscrewing the screw just behind it at the top, and there could be a couple of self tappers at the bottom.

The one covering the needlebar, which hasn't been removed here, is held on by just a simple thumb lever. Pull it down and the cover will lift off easily.

After the covers are all off, blow out the loose dirt and dust bunnies with compressed air or brush it out with a nylon cleaning brush.

Why bother?

I figure you would be wondering by this point why anyone would bother with a machine that has so many issues. 

Firstly, Husqvarnas are the only machines I've seen with a genuine low gear. When engaged, they go slowly and can punch through just about anything. The gearing is controlled by pushing (off) or pulling (on) the bobbin winder. The bobbin winder is always on.

Secondly, the patterns available are wonderful, and you can draw little dogs as well as yachts, and remember this is a mechanical machine designed in the 1960s. The patterns (which are covered cylinders) are easy to find because most people discard their machines when they get stuck (in reverse is very common), seized or break the pattern gear.

Problem areas

Pretty much everywhere there is original grease. 

All of the dials get stuck. I removed the pattern gear to get at the grease underneath it and discovered that it was grease-glued to the rod it's supposed to slide along. Everything that could be stuck was stuck, and since she used it ten years ago, it's just at 45 years from new and its time is up.

So knowing that all of the original grease needs to be dissolved, get to work. I work as a technician and have dealt with many of these machines. My own was stuck somewhere the others weren't, which is marked on this photo. 

Pay close attention to these

So, start brushing, keep clear of the paint and pay extra attention to these areas, testing by trying to turn the dials (be careful of solvent coming through the dials).

When the dials are all very free, and the machine is moving easily, there's one more area that will almost certainly be seized: The buttonhole mechanism. Your aim is to set the bottom dial (stitch width) to zero them try and pull it out to activate the buttonholer. I haven't seen one yet that isn't locked up tight. You will need to really work that mechanism, applying solvent, spraying oil etc. When you manage to finally get it pulled out, it also needs to be able to be turned between 0 and 4. As long as you don't apply too much force, you should be able to work the solvent etc through and the machine will be all good.

Make sure the reverse works and that the feed dog drops. Both should go easily and quickly. If there's a delay with the feed dog or the zig-zag, something hasn't been degreased.

Re-lubricate

Finish by making sure that everything you degreased has new grease (non-hardening teflon grease is an excellent replacement for plastic gears), and anywhere that metal touches metal will need oil.

With the new greases available, your machine should last a lifetime if lubricated. Just be careful with those plastic covers.

Motor

Remove the capacitor if there's one there (if you can't do this yourself, anyone who can solder can do it). It's for suppression purposes only and they're not needed in 2021. Check the brushes. If you want to, clean the carbon from the commutator with cotton buds dipped in methylated spirit while the brushes are out. Brushes less than a few mm long should be replaced, but bear in mind they last a really long time and the ones in the machine are probably the originals.

That's how to clean it

Most of these machines will be seized and/or the pattern gear will be broken. If you are so inclined, spend the time and money and the machine will make you fall in love with it.

The gears aren't nylon like Bernina gears (nylon absorbs moisture and becomes very brittle over time).
I hope that it is the seizing up then subsequent use that causes this. If your machine struggles to go, what would you do? You'd probably slip it into low gear and power ahead, right? *snap*
I'm hoping that this is it, because if so mine should outlast me.