Hi
My 9.9 yamaha outboard motor has faulty cdi-box. it used to work if i knock it little, so something is loose.
Does anyone ever try to remove that black potting? And if so, how it's done?
-welpester
Search "removing potting" in this forum. There have been a few previous threads discussing this. You can either remove it mechanically or chemically.
Ugh, yeah, used to repair Spelman High Voltage modules that were completely filled with resin in my first job back in the 90s.
To make a long story short: Theres no "chemical" way to remove it without damaging the parts or PCB that i know of.
If it's the soft stuff, you just remove it with a cutter piece by piece, hoping it does not stick to well to the plastic foils around caps etc.
The problem is, once you cleared the PCB, i may be impossible to tear the PCB from the resin underneath without breaking it.
If it's the hard resin: Forget about it. I'm not saying it can't be done, but it's a fools errand.
You use the hot air gun on your soldering station. When hot it becomes brittle so you can chip it off, it also loses attachment to the pcb so you can pull it off.
Basically you need: scalpel, dentist picks and safety goggles.
It's a lot of work, and you really really want to get in.
Wear safety goggles.
"box" dimensions are approx. Thickness 30mm, width 50mm and height 70mm.
Based on that, when i knock it gently, it works for a while. I think it might be some component leg/pin could be loose
on pcb. I could cut bottom plastic of the box. Then i assume that i can see pcb's bottom or least can remove potting
off from pub on that side and so on...
-welpester
Those hot air stuff, you need to be aware that its kind of approach is kind of irreversible process, box, casing may be deformed, messy and ugly outcome, internal components may be melted and damaged, no longer water proofing, casing cannot be closed up etc...
You should send a photo to them of the outboard motor so that they may be better able to advise you but YOU need to filter what you read.
This process as I know, is only used for reverse engineering, example it is never meant to be assembled back but you may be lucky if you did.
***READ BREAKINGOHMSLAW LAST SENTENCE*******
I've repaired and reverse engineered a bunch of potted brick HeNe laser power supplies. For the hard epoxy potting I've found that hot air and screwdrivers and dental picks work well. For the rubbery compound purely mechanical means work as well as anything, dig it out and scrape it off. If you have access to an xray machine that makes it much easier to map out where to dig so you don't mangle components. Often exposing the bottom side of the PCB is easiest and that may be all you need. On HeNe bricks that have a hard plastic casing I use a vertical mill to mill out a pocket where I know the bad solder joints are.
Often exposing the bottom side of the PCB is easiest and that may be all you need.
This is what I'm going to do
-welpester
If it is a hard epoxy resin, we have found two ways for removal. One is to use an old soldering iron and scrape away the resin, it crumbles once heated.
The best way we have found, is to use methylene chloride, an ingredient commonly used in paint remover. Build a dam up around the area to be removed, children's modeling clay can be used. Fill the area with paint remover, cover if possible as you don't want to breath the fumes. After a while, use a tool to scrape the resin free, it will turn to a rubbery-like material, it will peal off. Keep re-applying the chemical and repeat.
This technique was used to remove the potting compound from the old General Instrument Videocypher II modules.
Your potting compound could be silicon rubber, RTV, don't know how to remove it. However, one time I used RTV to seal a gasoline filler hose, after a while exposed to gasoline it turned to jelly. That was not our intent, but that might work too.
Any of these methods may also eat the color coding off of resistors, etc. Work very slowly.
Hope this helps - Jim
Often exposing the bottom side of the PCB is easiest and that may be all you need.
This is what I'm going to do
-welpester
Any field report?
Not yet. Motor is on my summer cottage, so first i have to get there
On next week or week after that.
I will report as soon as i get my hands on it.
-welpester