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Resistor repair to PCB - DIY 2

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Ingenuity

Ingenuity

Structural
May 17, 2001
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I hang out in the structural forums, so forgive me with this probably simplistic question for you EE's.

Our washing machine (front loader - which I dislike, but do not really wish to replace at this time - it is only 6 years old) recently stopped working with a 'LE' code. I found the problem - broken Hall-effect sensor that I removed. Looked similar to this:

sensor1_yvglrx.jpg


I removed the black rubber stuff to expose the PCB, and after testing, one of the SMD resistors (#681) has malfunctioned so I bypassed with new 680 Ω axial resistor. I re-checked the connection and all checked out to specs.

I reinstalled in the washer and all working ok. But this sensor is positioned near the motor stator on the back-side of the machine and if there was a leak through a bearing the sensor would get wet, so I want to replace the black rubber stuff.

sensor2_mp1hyn.jpg


Is 100% silicone sealant/caulking okay to use for this application?
 
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For this kind of DYI home repair 100% silicon will be OK. From the general looks the circuits on the board are low voltage. Just let the silicon set a couple days so the acetic acid (vinegar smell) is mostly gone. That comes about from a reaction to humidity in the air as the silicon sets. Most electronic grade silicon has none to low out gassing. Your module is open also so there will be no longer-term problems.

I've actually torn-down China made inverters, and found bathtub calk silicon (loaded with gypsum and impurities) used directly on the high voltage parts of the circuit boards. Not a good idea!
 
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Comcokid:

Many thanks for your detailed reply and explanation.

My 100% silicone is Made in the USA by GE - no 'Chinesium' here!



 
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I disagree with Comco and suggest against using the typical tube of Home Depot caulking... the acetic acid in the caulk can start a slow breakdown of any copper it can get to. I would prefer hot candle wax dripped into the area long before I would use caulk. Electronics-grade silicone cures in a different manner than the easy-to-get stuff, so it's not harmful to components.

Dan - Owner
Footwell%20Animation%20Tiny.gif
 
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Do a Google search for silicone potting compounds (not silicon). Silicone RTV (room temperature vulcanizing) sealants cure by reacting with atmospheric moisture and release acetic acid that will corrode electronics. These will not fully cure for months in layers as thick as yours. There are more expensive odorless grades that release methanol rather than silicone and these are what is used for electronics. But RTV is still an issue with thickness. Potting compounds are heat cured or two-part systems. Sealants are also designed to not sag after being placed in a joint. This is not what you want when you need to encapsulate electronic components.
 
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Hot melt glue (low temp) would work fine.
I you use silicone it must be non-acid cure. Yes the acid fumes will destroy Cu.

I hate our front loader also (door hinge is worn out and I can't adjust the water fill level) but it still works and new HE top load washers are nearly $1,000.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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The "electronics" grade of one-part silicone RTV releases methanol, so don't eat the uncured material. Bad news? Not cheap.

The alternatives will be difficult to remove if any other repair is desired.

Possibly a conformal coat would be sufficient. On Digikey it's available in small quantities with some having matching stripping materials in case it needs rework.
 
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Ed, just a week or so ago I replaced the drum in our Samsung front load dryer. Seems to be a known problem, Samsung did a piss-poor job of welding the seam, so after a few years of use it would split and start an increasingly louder thump thump thump. I figured it was better to spend ~1.5 hours and $250 replacing it myself than $1k for a new dryer (and likely close to that to have someone else do it). Surprisingly easy job, all things considered.

Dan - Owner
Footwell%20Animation%20Tiny.gif
 
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Hot Melt Glue absorbs water and becomes conductive eventually.

Acetic acid curing silicone is a disaster on boards rotting them in weeks.


Go to Home Despot and pick up a can of any Varathane that's water based and preferably clear. Either paint it on or spray it on.

Don't get me started on washers and dryers! I have a 165lb dryer sitting here, in the box, I have to somehow get on top of my washer to replace the dying dryer I've rebuilt 4 times.

Really don't get me started on the pathetic complete garbage bug-ridden crap user unfriendly interfaces Samscum is putting on their washers and dryers.

Keith Cress
kcress -
 
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3DDave; I looked at so many washers making sure I avoided Samsuck and eventually after reading a dozen users manuals found the best bet, only to discover I'd have to wait 5 months for that model to be available ANYWHERE, then, having to go back and do it again and again. Finally figuring out you have to see if the dryer is available and then figuring out if the user interface was at least fundamentally functional.

In all that I saw some that were WiFi enabled and that it only increased the cost a hundred bucks! At that I decided 'no thanks' but then sort of dropped paying attention to WiFi when it became a battle of availability. I guess what I'm trying to say is that since I ordered this thing in October and it came finally in mid December and it still sits in its box NOW while I paint the entire working laundry room and care for my elderly(92) mom I've completely forgotten if it has WiFi. LOL

Keith Cress
kcress -
 
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Keith,

Not sure if the Bosch-branded machines are available on your side of the pond, but in my experience they're better than average for reasonable money.

Ingenuity - if you're still looking for an RTV sealant, look for the 'neutral cure' types. They have a much longer curing time than the acetoxy (acetic cure) silicones but are unlikely to damage anything by corrosion. If you're in a position to choose, Dow's 3145 grade is an example which we used to use in sensitive applications where the acetic acid would have ruined the product. It's also remarkably heat-tolerant for a silicone, considerably higher than the commodity types.
 
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If you do, see if the model numbers and/or appearance have any correlation to the European models - I've honestly no idea if their US products share the base design with the European ones. Drop me an email nearer the time, you know where to find my address.
 
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