Wire wrap connections - cleanable?

[Hokieman]

My HK receivers are chock full of these wire wrap post connections for critical internal wiring. While a good solid connection, I'm speculating that it is possible for long-term corrosion and oxidation to cause the same kinds of problems that we see with pots and switches. I've done a bit of spot-spraying with de-oxit on one unit, and I'm wondering if this should be an extensive treatment for these type connections with a tip applicator De-Oxit? Thoughts?

 

[dshoaf]

Wire wrapping was a new manufacturing technology in the late 70s and almost all of the big vendors of that day used it to reduce labor costs and speed assembly. The problem after all these decades is that the metal-to-metal contacts have oxidized and/or reacted so that there may well be resistance across the junction.

I consider these to be potential sources of intermittent connections resulting in all sorts of strange problems. When I encounter one of these units, I resolder all of these joints. Yes, it takes bit of time but I don't try to troubleshoot the unit until its done. I'd chase my tail for hours.

Cheers,

David

 

[avionic]

Wire wrapping was a new manufacturing technology in the late 70s

Not entirely fact.. Try 1960..
http://en.wikipedia.org/wiki/Wire_wrap

 

[ryuuoh]

Get a solder flux pen. It's basically a sharpie with flux instead of ink. Makes spot applying a breeze.

 

[Hokieman]

When I encounter one of these units, I resolder all of these joints. Yes, it takes bit of time but I don't try to troubleshoot the unit until its done. I'd chase my tail for hours.

Do you just solder the upper portion where the wire comes off the post, or flow solder down the entire length?

 

[ryuuoh]

Solder the entire length, but don't over heat the parts. Have a look at this page:
http://amp8.com/tr-amp/hitachi/9500/ham9500o.htm

 

[jstang]

I second this ..... I do this on all my units with wire wrap.... I think it improves the sound as well......


jk

Wire wrapping was a new manufacturing technology in the late 70s and almost all of the big vendors of that day used it to reduce labor costs and speed assembly. The problem after all these decades is that the metal-to-metal contacts have oxidized and/or reacted so that there may well be resistance across the junction.

I consider these to be potential sources of intermittent connections resulting in all sorts of strange problems. When I encounter one of these units, I resolder all of these joints. Yes, it takes bit of time but I don't try to troubleshoot the unit until its done. I'd chase my tail for hours.

Cheers,

David

 

[dshoaf]

Not entirely fact.. Try 1960..
http://en.wikipedia.org/wiki/Wire_wrap

Fair point, Avionic. It was a new technique for consumer gear, for sure!

Cheers,

David

 

[John James]

I worked as a computer operator for what was then the largest bank in N.C. from 1968 until 1970. We had IBM 306 Main Frame computers. The in-house tech. would do PM during the 2nd shift which I worked. He would pull cabinet covers off and expose a panel about 5 ft by 3 ft with a forest of brass pins about 1/4 inch apart. He would then refer to notes and start to remove some wires and install others with a wire wrapping machine that looked like a pistol. To a 19 year old, it was just amazing. The pins were identified by a row of numbers up one side and another row across the top. Tese numbers ran into 3 digits. lots and lots of pins and wrapped wires!

 

[Hokieman]

This confirms what my engineer's brain was telling me - that these things were just as likely to have long-term corrosion issues as switches and pots. This will be a standard long-term HK remediation effort for me. Future pic post opportunity.

 

[Arkay]

I've read that these things were wrapped tightly enough to create metal-to-metal "welds" around the corners (which is why they used square posts, not round ones) which function much better than solder connections.

But I have seen them get rather dirty and corroded around the visible spaces between the wires, and long suspected that some degree of corrosion could work its way into those "welds". Therefore, I always blast all of them with contact cleaner, and on the most critical gear, with DeOxit. It does seem to improve things, and looking at them with low-power microscopes, they do get cleaner.

Now I have conflicting advice: 1. Don't solder them, as you can adversely affect the intrinsically better "weld". 2. Solder them, to create a bigger/better contact.

Which is right? I'd really like to hear a specialist metallurgist's answer, based on actual research. I'm tempted to look for some kind of conducting oily-silver solution to apply to them, to "fill the gaps"... or maybe I'll start soldering them, after really thorough cleaning.

Hhhhmmm....

OH, but I WON'T solder over the ones in my Yammie M2; all those wires and posts are silver (not copper), and silver oxide is a decent conductor, so as black as they get, they still perform well, better than solder, actually!

 

[avionic]

I've read that these things were wrapped tightly enough to create metal-to-metal "welds" around the corners (which is why they used square posts, not round ones) which function much better than solder connections.

Wirewrap pins are indeed square.Usually a BeCu alloy for reduced corrosion. Going one-step further in high reliability applications they were gold plated for corrosion resistance. More reliable than solder.:yes:

 

[charliemcd]

I would leave them alone in general unless there is a really obvious issue. I've read that when the wire is wrapped around the post, a gas-tight contact is made with the post corner biting into the wire. Say you've got 5 complete wraps arond the post. Multiply that contact point by 20 (4 corners x 5 wraps) and that's a lot of metal-to-metal joints.

What you SEE is just the exposed surfaces of the post and the wire, and I rarely see any significant signs or tarnish or corrosion on them, but even if you do see any, that's probably not indicative of the condition of the contact points.

My $0.02, YMMV.

 

[qboneus]

I would leave them alone in general unless there is a really obvious issue. I've read that when the wire is wrapped around the post, a gas-tight contact is made with the post corner biting into the wire. Say you've got 5 complete wraps arond the post. Multiply that contact point by 20 (4 corners x 5 wraps) and that's a lot of metal-to-metal joints.

What you SEE is just the exposed surfaces of the post and the wire, and I rarely see any significant signs or tarnish or corrosion on them, but even if you do see any, that's probably not indicative of the condition of the contact points.

My $0.02, YMMV.

+1
This is what I was taught as well, leave wirewraps alone unless you can physically shift them with slight pressure from your finger or you specifically have some reason to believe that an issue you are having is caused by a failing wirewrap.
If you are really in question I would say break out the multimeter and ohm out the connection from the base of the pin to the end of the wirewrap right before it enters the insulation; next apply slight pressure to the ww while ohming the connection to see if the value changes
if nothing changes, I would change nothing.
Tal