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Cleaning Card Edge Connectors?

T

troj

Experienced Member
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Apr 22, 2018
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115
Location
Bellevue, NE
So the Expansion Interface on my Model 1 doesn't appear to be working properly. First thing I want to do is thoroughly clean the card edge connectors. They're pretty gunked up and an eraser doesn't seem to be having much impact.

Are there other methods recommended?

-Kevin
 
Emery cloth on gold plated contacts? You probably shouldn't use anything more abrasive than jeweler's rouge--the plating is usually only about 9-11 microns thick and very soft. There are polishing cloths made for that and they're inexpensive if you have to use an abrasive.
 
The contacts on this system look to be tin, not gold-plated. I've got some grey corrosion that's proving problematic.

I'm hoping to avoid anything abrasive, if possible. I'll go that route as a last resort.

-Kevin
 
Are the contacts on the connectors also tin-plated? Gold+tin is not the best combination in the world.

As to hardness of fiberglass (in moh):

fingernail (hardness = 2.5)
copper penny (hardness = 3)
glass plate or steel knife (hardness = 5.5)
steel file (hardness = 6.5)

Personally, I'd try a paste of baking soda (2-3 moh) and water, rubbed and rinsed well.
 
Last edited:
A fiberglass pen is more akin to a brush than a knife, nor is it woven like a Brillo pad.

It has flexibility and you use a light touch. Jewelers and watchmakers use them to remove corrosion as well
 
Chuck(G) said:
Emery cloth on gold plated contacts? You probably shouldn't use anything more abrasive than jeweler's rouge--the plating is usually only about 9-11 microns thick and very soft. There are polishing cloths made for that and they're inexpensive if you have to use an abrasive.
Click to expand...

You're right. I must be getting old. I would never use Emery for this. What I meant to type was crocus cloth. It's 800 grit and works very well for this.
 
This topic was covered in The Custom TRS-80 many moons ago and the solution was a pink pearl eraser and then some contact cleaner.

Over the years I found the solder on the connectors gets so thin the copper underneath gets exposed and you need to re-tin them which not a job for a faint hearted. After you re-tin them you need to smooth them down with 800 paper so they are thin enough for the cable to easily slide over them.

DeoxIT looks ideal. Try that first, or a pink pearl eraser then DeoxIT.
 
While Deoxit is good stuff, I've had better results with DC#4 ( Dow Corning # 4 silicone grease ).
As an example, I had a ZX81 with RAM module attached. The slightest bump and the program was lost. I put the DC#4 on the contacts and one could bounce the ZX81 off the table without any issue with the program getting corrupted.
I suspect that other dielectric greases might work but DC#4 has always worked well for me.
Dwight
 
I use dielectric grease on auto electrics extensively. Never tried it on an edge connector, but it might work well. You can find the stuff at auto supply stores and big-box stores with auto departments. Loctite and Permatex brands are common and are probably the same stuff.
 
I have gotten to not even use erasers on gold, let alone a fiber glass brush. If the oxide is causing problems, while vinegar rubbed on and then washed off often works well. You might soak it for a few hours but I've found it leaves a film if soaked too long.
Dwight
 
Except in the case of HP41 battery packs which must contain Aqua Regia... I suppose mercury batteries might be an issue for gold contacts as well.
 
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