VBM Super Domobar Water Reservoir Switch Meltdown

Equipment doesn't work? Troubleshooting? If you're handy, members can help.

#1: Post by Buffalono »

Hello everyone, first post here. I picked up this machine off eBay. It was listed as in need of repair so I figured I'd take a chance on it because the price was decent. I've gotten it in pretty good working condition. It needed a vibe pump, group head rebuild and cleaning and descaling. It was a great upgrade from my Silvia and I could finally make decent espresso. A couple days ago I noticed the low reservoir water light would stay on even when the reservoir was full or when I lifted it off the switch. The rest of the operation of the machine was not affected so I figured the switch was shorted out in the on position. I opened it up and sure enough that was the case.

I'm attaching photos of the poor condition of the switch. It looks like it overheated. So I'm checking here to see if there's anything that I need to look into before I replace the switch. Like I said the machine was working fine other than the low water reservoir lights staying on and the switch not turning the machine off when I lifted the reservoir off the plate. The schematic shows switch in line with the power main so I can see why the meltdown.

The resistance of the heating element seems to be in spec, it's 8.5 ohms while still connected to the circuit. The only reason I can think of the switch meltdown is maybe the insulation on the wires and connectors broke down or from leaving the machine on for 8 hours at a time sometimes. I have it on a smart outlet rated for 15 amps. I'm going to run new wires and connectors as well as replace the switch, is there anything else I should check or replace?

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Randy G.

#2: Post by Randy G. »

VBM made a mistake with that switch. Don't know about the current version, but in the one I had, the current for the entire machine flows through it. There area lot of ways to stop the machine from working if the water gets low in the reservoir, and IMO, that is the worst one. Likely, the contact area in the switch is small and so every time it shuts off the power it damages the contacts and eventually it fails. If you want a more permanent solution you will have to wire the switch through a relay.

ADDENDUM: There are two possible caused of melted switches such as yours. The first might be arced/carbonized contacts inside the switch reducing the conductive area of that are already small contacts. The second can be oxidized or corroded external connection points. Either of these causes resistance and thus heat. I can professionally and personally recommend Caig Industries product called "DeOxitD." Their D5S-2N is perfect for such use because the nozzle has an adjustable valve so you can more accurately control the flow. It is safe for plastics. I have recommended it to numerous Hottop users and every single one (with one exception) has been able to 'resurrect' their non-working control panel switches. The one exception was likely a bad solder joint. It also helps prevent future oxidation as well.
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Buffalono (original poster)

#3: Post by Buffalono (original poster) »

Thank! That exactly what I thought when I checked the schematic.

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#4: Post by cafeIKE »

The problem is caused by corrosion on the contacts. Caused by either poor maintenance or sloppy filling.
They overheat and eventually get beyond the switch rating.

IMO, switching the entire machine current is wrong.
It's to protect idiots from themselves.

I change my machines so only the low water light illuminates.

Use a Faston Y for the power.

These connectors are over 15 years old and run 10+ hours/day 365 days a year:

Do it right. Do it once.

Buffalono (original poster)

#5: Post by Buffalono (original poster) »

Thank you very much for the repair solution. It is very helpful to not have to re invent the wheel.