# Help identifying plating



## akgold (Jul 29, 2015)

I am processing a 1971 mainframe remains. It was a Burroughs B2700. It has many large backplanes (wire-wrap) that range up to 3 x 3 ft. Most of them have gold plated pins that mated with gold edge connectors. However some have another plating. These can be a complete backplane or can have one row or more of gold interspersed with these others that, after several years of weathering, are a light gray. They are not black like tarnished silver but a light gray. The entire pin is the same plating. Even the mating surfaces where the gold edge connectors socketed. It is not nickel. I am unsure what I have. I suspected cadmium but that does not seem likely. I am not sure what to test with at this point. These pins were wire wrapped with silver plated wires. It does not look like solder either. Never seen this color or plating. I was going to throw it in with the rest to go to the smelter but not sure it is worthy it at this point. Any ideas?


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## jimdoc (Jul 29, 2015)

Do you have DMG to test for palladium?


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## g_axelsson (Jul 29, 2015)

It could be tin plating. Does it dissolve in HCl?

Is it only the back planes or is it a complete computer? Old machines as these could easily be worth money for collectors.

Göran


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## akgold (Jul 29, 2015)

jimdoc said:


> Do you have DMG to test for palladium?




I don't have much of anything out here where we are pulling this stuff. I will have to wait until I can make a trip back to civilization to lay my hands on any supplies. Bush Alaska, you know. Stone ages!


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## akgold (Jul 29, 2015)

g_axelsson said:


> It could be tin plating. Does it dissolve in CHl?
> 
> Is it only the back planes or is it a complete computer? Old machines as these could easily be worth money for collectors.
> 
> Göran



Only pieces. The big steel frames. Boxes of boards (several hundreds), backplanes, blower motors, transformers, and for the collectors..the ferite memory stacks. I think there were 4 but I have only found 2 of them. But there are several piles left to go through. We are sorting and crating to get all of it loaded up to take back to town. Along with a couple hundred thousand pounds of other electronics. From the 2000's all the way back to the 50's. It is like Christmas all day. But I am getting old and tire easily. Even with all of this neat stuff my enthusiasm sometimes takes a hit!


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## akgold (Jul 29, 2015)

g_axelsson said:


> It could be tin plating. Does it dissolve in HCl?
> 
> Is it only the back planes or is it a complete computer? Old machines as these could easily be worth money for collectors.
> 
> Göran



I did not answer about the tin. Don't have any supplies out here. But would any manufacturer use tin plated contact surfaces to mate with gold? In the same machine/backplanes where most of them are gold contacts? For the same boards? That would be strange to me, especially at a time where pms are cheap. It really does not look like tin.
Also, originally the machine took 3 26ft U-hauls and 6 pickups to move from Anchorage where it was the Alaska Railroads first large computer. You could run a small city with the blower motors that came from the frames. 
Steve


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## glorycloud (Jul 29, 2015)

I would imagine that the backplanes will bring some good money to the right scrap buyer.
Some of the boards will have gold finger tabs on them as they would marry up to the gold
female connectors some of the back planes.


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## akgold (Jul 29, 2015)

glorycloud said:


> I would imagine that the backplanes will bring some good money to the right scrap buyer.
> Some of the boards will have gold finger tabs on them as they would marry up to the gold
> female connectors some of the back planes.



All of the boards have or had gold fingers on them. A lot of identical boards. But some were plugged in to parts of the backplanes that had gold sockets (pins) and other identical gold fingered cards right next to them plugged into slots that had this other plating. I just find it unusual that a gold fingered card would be plugged into a backplane that had tin plating on one slot and the identical next slot with an identical board would have a gold plated slot. Somehow it does not seem to make much sense to me given the low price of gold at the time. The color and texture of the pins and mating surfaces just don't look/feel like tin. To my eye, tin just doesn't normally display as a gray, almost powdery surface. Especially after several years of weathering. It almost looks closer to weathered lead.
There are several hundred pounds of these backplanes. More than half had all gold plated pins. At this point all are going to the smelter. Too much work to separate and try to process differently. I'll be very lucky to try and clean. process, and crate many thousands of pounds in the short summer left up here. I am just too old and slow now.


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## macfixer01 (Aug 1, 2015)

Akgold,
Have you pulled out any of the pins that don't have visible gold and looked at the contact area? I just bought some old Burroughs backplanes which are a little different than what you have. They're about 3x2 feet and the sockets are 4 sets of long flexible black plastic strips, mounted in an aluminum frame. Instead of circuit boards though, these once held small gold plated frames each filled with several discrete components. I found a small picture online of a module that looks similar to one she found to show me (with the green plastic on it). Anyway the reason I ask is that my pins are copper with what seems to be tin plating thick enough that it peels off if you bend them, and they have only one small round dot of what I believe is 24K gold right at the contact point? While in the socket you can't tell they have any gold at all. The pins came out looking dark and corroded for some reason in this photo, they're actually a light gray similar to your pins.


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## GOLDbuyerCA (Aug 2, 2015)

From my experience , taking one of these apart, " and it is a lot of work " major job. i found the plating to be 10 micro inches of Gold, and 10 to 15 micro inches of Palladium . 50 an ounce for Gold, and 35 an ounce 
for Palladium in that time period. the builders, actually bought their precious metals, years ahead, to smooth price fluctuations, there cost may even be lower, by say 25 to 40 percent. 

there is good hook wire in thee units, as you say silver plated wire, capable of wire wrap, a gas tight seal, that is why the plating thickness is so thin, " quite disappointing , i found " 
i found the cards that plug in, to be 20 micro inches, and had value, good score getting one of these. but the plating thickness is not so great, and the whole job is a lot of work. ' my opinion "


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## Anonymous (Aug 7, 2015)

jimdoc said:


> Do you have DMG to test for palladium?



I think Jimdoc has the right idea here. some of these older mainframe backplanes used palladium instead of gold, and rather a lot of it.


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## macfixer01 (Aug 17, 2015)

If anyone is interested I put together a short video on taking apart those Burroughs backplanes I got recently, and made a couple simple tools to use on them. The backplanes are a strange design, 56 separate blocks of black plastic mounted in a steel frame. The frame scratched easily and looked like aluminum, but I found it's magnetic so apparently only steel.

https://www.youtube.com/watch?v=cbsrMh7npaE

macfixer01


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