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Unexplained Corrosion between a midi cable/plug and a socket
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Unexplained Corrosion between a midi cable/plug and a socket
Blairio
Yesterday I was trouble shooting a midi issue in my setup. This involved unplugging midi cables that had been untouched for two years or more and substituting a brand new cable.

Everything was going smoothly until I tried to unplug a cable running from a midi splitter box into my mopho keyboard. The plug was extremely reluctant to come out (I needed slow & gentle persuasion and switch lubricant), and when it did there were clear signs of corrosion on the plug pins and the plug outer screen,

The Mopho keyboard is connected via its Poly Out socket to my DSI Tetra. Both the plugs / sockets at either end of this link cable were also affected, with verdigris clear on the plug pins.

No other devices connected via midi to the midi splitter were affected - in fact no other devices anywhere in my setup were affected like this.

My room is bone dry, with normal humidity. Could there be an electrical explanation (some kind of galvanic transfer) for the corrosion I found?

This is one for folk who know more about electrics / electronics than me.
Graham Hinton
Blairio wrote:
The Mopho keyboard is connected via its Poly Out socket to my DSI Tetra. Both the plugs / sockets at either end of this link cable were also affected, with verdigris clear on the plug pins.

My room is bone dry, with normal humidity. Could there be an electrical explanation (some kind of galvanic transfer) for the corrosion I found?


Yes, whenever you have a junction of two dissimilar metals you can get electrolytic action. The only details relevant are the metals of the connectors where this happened, not the equipment. If you mated gold plated contacts with non-gold such as tin the plating can get stripped off and expose the more active metals beneath.

Bone dry is not normal humidity. The air humidity can be an electrolyte particularly near the sea or a swimming pool, but spilt beverages also factor.
Blairio
Thanks John. Yes, 'bone dry' was a bit of hyperbole. My music room adjoins my kitchen, so I guess there could be humidity from there, but the house is well ventilated, and my asthma would certainly pick up on unusual humidity as effectively as a moisture meter!

On examining the midi sockets, they appear to unaffected - it is just the plug pins which appear to have sacrificed themselves. I have fitted new midi cables and I'll check those connections every few weeks for signs of the problem returning.
Rex Coil 7
Graham Hinton wrote:
Blairio wrote:
The Mopho keyboard is connected via its Poly Out socket to my DSI Tetra. Both the plugs / sockets at either end of this link cable were also affected, with verdigris clear on the plug pins.

My room is bone dry, with normal humidity. Could there be an electrical explanation (some kind of galvanic transfer) for the corrosion I found?


Yes, whenever you have a junction of two dissimilar metals you can get electrolytic action. The only details relevant are the metals of the connectors where this happened, not the equipment. If you mated gold plated contacts with non-gold such as tin the plating can get stripped off and expose the more active metals beneath.

Bone dry is not normal humidity. The air humidity can be an electrolyte particularly near the sea or a swimming pool, but spilt beverages also factor.


That said, I suppose it comes down to either the particular MIDI cable used or whatever MIDI sockets Dave Smith elected to install in those particular devices.

If I'm properly understanding the described situation, it seems as though the DSI sockets may be the culprit. I wonder if those DSI devices have some sort of ~gold plated~ pin sockets? Gold is soft, wears through easily. Once the gold is worn away the unprotected metal is exposed.

seriously, i just don't get it
Rex Coil 7
Blairio wrote:
Thanks John....
(his name is Graham). nodnod
Blairio
Rex Coil 7 wrote:
Blairio wrote:
Thanks John....
(his name is Graham). nodnod


Argh! Schoolboy error. I have a work colleague called John Hinton. Apologies, Graham.
Blairio
Rex Coil 7 wrote:
Graham Hinton wrote:
Blairio wrote:
The Mopho keyboard is connected via its Poly Out socket to my DSI Tetra. Both the plugs / sockets at either end of this link cable were also affected, with verdigris clear on the plug pins.

My room is bone dry, with normal humidity. Could there be an electrical explanation (some kind of galvanic transfer) for the corrosion I found?


Yes, whenever you have a junction of two dissimilar metals you can get electrolytic action. The only details relevant are the metals of the connectors where this happened, not the equipment. If you mated gold plated contacts with non-gold such as tin the plating can get stripped off and expose the more active metals beneath.

Bone dry is not normal humidity. The air humidity can be an electrolyte particularly near the sea or a swimming pool, but spilt beverages also factor.


That said, I suppose it comes down to either the particular MIDI cable used or whatever MIDI sockets Dave Smith elected to install in those particular devices.

If I'm properly understanding the described situation, it seems as though the DSI sockets may be the culprit. I wonder if those DSI devices have some sort of ~gold plated~ pin sockets? Gold is soft, wears through easily. Once the gold is worn away the unprotected metal is exposed.

seriously, i just don't get it


In terms of mechanical wear and tear (plugging & unplugging cables) neither my Mopho Keyboard nor the Tetra have been subject to much of this. They were set up around 6 years ago, and hardly touched since. Therefore there is little opportunity for plating on either plug or socket to wear through.

From schoolboy physics: Gold is far less reactive than nickel or tin - or whatever the average midi plug pins are plated in. Therefore the more reactive element will be subject to sacrificial oxidation. So yes, I don't know what metal or coating the Dave Smith sockets employ, but they appear to be less reactive (higher quality) than the stuff the cable plugs are made out of. This suits me fine, as it is easier to replace a midi cable than a midi socket soldered onto a circuit board.
TheDegenerateElite
Some cheapass cables are made from really junk metal, and copper plated aluminum wire.


Generally, going cheap on cables will usually bite you at some point.


Anymore, I buy a couple of good cable, with repairable connectors with every piece of gear I order. Gradually replaced all the yardsale, Radio Shack, guitar cable crap I had accumulated over the years.
Blairio
TheDegenerateElite wrote:
Some cheapass cables are made from really junk metal, and copper plated aluminum wire.


Generally, going cheap on cables will usually bite you at some point.


Anymore, I buy a couple of good cable, with repairable connectors with every piece of gear I order. Gradually replaced all the yardsale, Radio Shack, guitar cable crap I had accumulated over the years.


That sounds like a plan. For my part, my current cables seem well up to the job, except when connecting to, or between, items of DSI gear. I'm going to push the boat out and get a couple of high quality midi interconnects for these devices.
Pelsea
Some observations on oxidation.
Most plug shafts are made of steel or brass, which is nickel plated then then treated with a chromate solution or plated again with tin or gold. Springy contacts are made of some variety of brass and similarly plated. The nickel prevents the base metal from corroding and the outer coat prevents the nickel from oxidizing. Tin will oxidize, but the oxidation layer is so thin that electrical conductivity is not affected. (Bare nickel develops a thick, resistive oxidation layer.) Once the plug is in use, scratches in the coating produced by insertion expose the nickel to air and oxidation begins.

There are several things that can expose the nickel to oxygen.
A poorly designed socket that encourages scratching.
Thin gold plating.
Badly done plating of gold or tin resulting in “nanopores” that expose the nickel.
Badly done chromate bath. This has recently become more of a problem since the old standby chromates have been declared no-no by RoHS.

Once the nickel has been exposed, oxidation is accelerated by:
Heat.
Moisture, especially if it has a bit of salt.
Sulfur compounds in the air (common if you heat with coal).
Clorine in the air (swimming pools are death to electronics).

Certain types of treatement are appropriate for particular applications:
Gold is best in low current (audio and digital) connectors.
Tin is best in high current connectors.
Chromated nickel is best for connectors that will be disconnected a lot. (The durability of gold is specified in 100s of cycles, while nickel is good for 10,000 or more.)

A gold connector that is just left alone will last you the rest of your life, wheras a nickel connecter in a box will be fuzzy after a decade.

Some lubricants will prevent corrosion by reducing the scratching and by sealing the mating areas from oxygen.
MindMachine
TheDegenerateElite wrote:
Some cheapass cables are made from really junk metal, and copper plated aluminum wire.


Generally, going cheap on cables will usually bite you at some point.


Anymore, I buy a couple of good cable, with repairable connectors with every piece of gear I order. Gradually replaced all the yardsale, Radio Shack, guitar cable crap I had accumulated over the years.


Totally agree, but would like to say that I never had a corrosion issue (some just broke though) with any Radio Shack connectors (cords or adapters) and some are 30 years old. They are still far superior in quality than the vast majority of cheap ass cables on the internet (and they should be, because they were never that cheap).

I have some 1970's Tascam mixers that have had the RCA connectors tarnish some, but they are still usable.

Like MR. Hinton and pelsea stated, I think the environment (moisture/salt) will turbo charge any issues between dissimilar metals.

Hopefully your DSI units are unscathed and you can clean them up a bit and get many more years use. They are lovely machines.
Blairio
MindMachine wrote:
TheDegenerateElite wrote:
Some cheapass cables are made from really junk metal, and copper plated aluminum wire.


Generally, going cheap on cables will usually bite you at some point.


Anymore, I buy a couple of good cable, with repairable connectors with every piece of gear I order. Gradually replaced all the yardsale, Radio Shack, guitar cable crap I had accumulated over the years.


Totally agree, but would like to say that I never had a corrosion issue (some just broke though) with any Radio Shack connectors (cords or adapters) and some are 30 years old. They are still far superior in quality than the vast majority of cheap ass cables on the internet (and they should be, because they were never that cheap).

I have some 1970's Tascam mixers that have had the RCA connectors tarnish some, but they are still usable.

Like MR. Hinton and pelsea stated, I think the environment (moisture/salt) will turbo charge any issues between dissimilar metals.

Hopefully your DSI units are unscathed and you can clean them up a bit and get many more years use. They are lovely machines.


That's the weird thing. The midi sockets on my Mopho keyboard and Tetra are totally unscathed, while the offending midi cables are now in the bin. And yes, the Mopho / Tetra combo sounds great (I call it my Prophet 5) and is pleasing to use. I have had it for 7 years now, and it has become part of the studio. There has been no reason to unplug & move either unit, hence the 'galvanic voodoo' has had a good opportunity to take hold.

I have had one other midi cable issue recently: I had a 3 metre cable running from my powered midi splitter box into my Doepfer Dark Energy mk1. No problems atall. I used it to hook my new Yamaha Reface DX up to my system, and ... nothing, except for the odd hung note. I plugged the cable back into The DE, and it worked just fine.

Out came a fresh 3 metre cable for my Reface DX, and it works perfectly. So basically:

1. the Reface DX is very twitchy about its midi feed.
2. not all midi cables are created equal.

I used to buy high quality midi cables for live work but use whatever was lying around at home for my studio. It looks like I need to reappraise that approach.
Blairio
A rather sorry development with my DSI Tetra. After singing its praises last week, I switched it on yesterday to find that the filter on one of its voices was acting up - emitting a whistle and not tracking properly. I figured it was Voice 3 at fault. I tried running the onboard calibration routine (for VCOs and filters) and sure enough it stuck at Filter 3.

I took the back off it in the vain hope that any chips would be pushed into housings on the circuit board, but no such luck - everything is SMT. It is going off to my local tech later in the week to see what he can do.

I also examined the midi sockets - in one of which a midi plug had developed corrosion - and found what looked like 'sweat' on the plastic bodies - even the 'thru' and 'out' sockets which had nothing plugged into them. The metal connectors were clean but the 'sweat' looked distinctly odd. They are all cleaned and dried off now, and the issue is secondary to the loss of one of the Tetra's 4 voices. Maybe I need to look for a new compact analog-poly solution.
Blairio
Reviving this thread to report what I hope is the final chapter in my midi cable / socket corrosion woes.

After my Tetra's voice 3 filter issue was fixed, I enjoyed a brief period when the synth worked fine. Gradually however its midi triggering became increasingly random, and it wouldn't even load fresh firmware, so back it went to Sequential (and a very helpful guy called Carson Day) to have all its midi sockets replaced.

UPS and British customs worked their usual evil magic, but eventually I got my Tetra back, complete with the latest firmware update.

I plugged it into my Mopho keyboard and ..... the triggering issues were still there! An extended period of anglo-saxon expletives followed (very cathartic), until common sense prevailed and I tried triggering my Tetra from other sources. It worked perfectly.

So the issue lay within my Mopho keyboard. I removed the main circuit board and sure enough, just like my Tetra, all three midi sockets had the tell-tale film of 'sweat' on them and I could see corrosion in the sockets themselves.

Sequential offered to repair my Mopho Keyboard for their usual flat fee of $25 (which I reckon is great service), but Carson offered an alternative - he would mail me some new sockets for the cost of the postage, and I arrange for my local tech to fit them. I decided on this, because I have lost patience with UPS. Basically after 10 days elapsed I had to contact them to learn that they wanted additional paperwork to release my Tetra, and were all set to charge me day on day for 'storing' my synth. Grrr.

On the plus side, Sequential have supported me as a customer very well, and I know my Mopho Keyboard and Tetra will be fighting fit for many years to come.

That just leaves the mystery of the 'sweating' midi sockets.
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