Omnibus backplane lubrication

[thunter0512]

What is the best type of lubricant for Omnibus backplanes?
It can be a struggle to insert and remove PDP-8/e boards into the Omnibus.
There is a risk of damage to the brittle bakelite connector housings on the Omnibus PCB.
Traditional contact sprays should work but have two problems:

1) they remain wet and over time will attract and retain dust
2) the solvent and lubricant may weaken or attack the bakelite

There are some PTFE (Teflon) based lubricant sprays which create a dry film. Would this type of spray work?

Any suggestions what I could use which reduces the strain on the Omnibus and the PCBs during insertion/removal without creating new problems?

Thanks and best regards
Tom Hunter

 

[AK6DN]

For cleaning and maintaining gold finger boards I use the DeoxIT Gold wipes from CAIG Labs: https://caig.com/deoxit-gold-g-series/ and their other products for repairing really corroded contacts.

 

[Roland Huisman]

The only thing you can consider is to check the V shape at the edge connector. You can use a file to adjust this a bit. But I would never use any lubricant.

 

[thunter0512]

The only thing you can consider is to check the V shape at the edge connector. You can use a file to adjust this a bit. But I would never use any lubricant.

Thanks Roland,

I am curious about your comment "But I would never use any lubricant".
Could you please explain the reason?

The Deoxit Gold-G recommended by AK6DN looks like it is meant to be used for this exact purpose.

I also found the following which looks promising:

https://www.mgchemicals.com/products/contact-cleaners/super-contact-cleaner-with-ppe/

I was concerned about the Bakelite connector housing after having pulled some boards repeatedly during the core memory board debugging and repairs. I also lost bits of skin a few times. :-(

Thanks and best regards
Tom Hunter

 

[Roland Huisman]

Lesson learned, never press quote when writing a reply. :-( It completely deleted my story.

To my understanding a lubricant is always leaving a residue. For now it will probably work fine, but over time it always seem to give problems. I have opened several switches which a contact grease. That worked fine, but over time it hardened and made switching impossible because the contacts could not make contact anymore. Standard contact sprays are forbidden here in my workplace. These always seem to solve things temporary. Contact spays seem to eat contacts over time. So you have to clean the surface after using a contact spray. But you can't remove the spray when it is creeping into little holes. It sits there for ever eating your metals.

Deoxit seems to be a different story, but I have never used it on any contacts. If a connector is bad, replace it. If a potentiometer is bad, also replace it. I know, sometimes it can be hard to replace things, but don't soak it in a spray.... In the end you will end up with more work. But that is my experience... Deoxit fader spray seems to be a good one, but I don't have long time experience with that...

I was concerned about the Bakelite connector housing after having pulled some boards repeatedly during the core memory board debugging and repairs. I also lost bits of skin a few times. :-(

I know the problem. I have once seen a tool like this one. But I don't know if it was original DEC. But I think it gives you a lot more control over what your board does in the backplane.


Regards, Roland

 

[thunter0512]

...
If a connector is bad, replace it. If a potentiometer is bad, also replace it.
...

The question was really just about lubrication to make insertion and removal of PDP-8/e boards easier.
I fully agree with your comments about bad/dying parts and that you should just replace them rather than trying to apply a bandaid which last a short time and sometimes even makes the problem worse.

I have now ordered both the Deoxit Gold-G liquid with brush applicator and the polyphenyl ether spray from MG and will apply each to one board and then report back about if/how it improved board insertion/removal. My plan is to apply both only to the board connector edge not the Omnibus backplane connector. I don't know how Bakelite would react with either of the lubricants and associated solvents. Better safe than sorry.

Best regards
Tom Hunter

 

[djg]

I've used both of the products you listed with no obvious problems. I wipe them on the edge fingers with a paper towel so they go where I want and I have some control on how much. Also cleans a little.

I've also used https://www.nyelubricants.com/nyogel-760g. It seems to be the best at making things move easily but also leaves the most residue since it is a grease. I think the MG leaves the least residue. I would start with it and move up if you find them still to hard to insert/remove. I have seen damage to some of my backplanes from people being too rough.

 

[Roland Huisman]

The question was really just about lubrication to make insertion and removal of PDP-8/e boards easier.

I know, but I wanted to point to possible problems in the future... Lubricating stuff can work great for now but might have unintentional problems in the future. That was the point I was trying to make...

I have now ordered both the Deoxit Gold-G liquid with brush applicator and the polyphenyl ether spray from MG and will apply each to one board and then report back about if/how it improved board insertion/removal. My plan is to apply both only to the board connector edge not the Omnibus backplane connector. I don't know how Bakelite would react with either of the lubricants and associated solvents. Better safe than sorry.

Applying to the PCB contacts only sounds a lot friendlier indeed. let us know how things go...

 

[vrs42]

It can be a struggle to insert and remove PDP-8/e boards into the Omnibus.
There is a risk of damage to the brittle bakelite connector housings on the Omnibus PCB.

Hmm. Is this a problem mainly with a board or two, or with all of them?

I have a fair amount of experience with boards binding, and even breaking the corners of the Bakelite. Mostly boards that I or someone else had made to fit the backplane. There is a narrow tolerance, since the gold fingers run right next to the edge of the edge connectors.

A slight warpage to the backplane occurs in one of my 8/A backplanes,, together with some alignment issues of the card guides due to the cage being dropped in shipping. That's the worst, as it makes all the cards hard to insert. The fact that it's an 8/A, so some of the cards are hex height, makes things even worse.

In the 8/E, my problems have been fewer, and usually with the boards themselves. A certain minimal "play" of the edge connectors within the receptacles is required, allowing one to "rock" the board slightly clockwise or counter-clockwise when it binds. You want to be able to unbind the connector, but not to get one side of the board more than an eighth of an inch or so ahead of the other. With the length of board as a lever arm, this translates to sub-millimeter movements within the edge connector, mostly involving the right and left edges of one or more of them.

Another minor thing that helps an astonishing amount is to bevel the right and left corners, so that the board will try to self center when inserted, as well as a bevel on the front and back edges, which allows the board to gently open the metal fingers in the receptacle, rather than jamming a sharp corner into them.

If it's just a stubborn board or two, a couple passes of an emery board or the like on the edges of the edge connectors may help. Work carefully and don't get carried away though, as it's very difficult to add material back! I had a couple of board runs that did a lot of binding, back when I was getting the edge connectors right, and I've seen a couple of other folks have the same issue. Shouldn't be much problem with DEC boards, unless something's gotten warped.

Oh, and this comes up in the flip-chip tester, where you solder in the new receptacles. You definitely want to use a proper double height module and leave it inserted when soldering the connectors. Even a little offset between them will get soldered in and make it forever a bitch to get modules in and out!

I haven't had a lot of need for the lubricants, except for one keyswitch that was full of sludge when I got it.

Vince

 

[thunter0512]

Hmm. Is this a problem mainly with a board or two, or with all of them?

All the boards seem to be a unusually tight fit.
To remove a board I gently try to lift each side a little at a time. It eventually releases and I leave some of my skin behind on one of the boards next to the one I removed.
To insert I try to centre the board and then push down with the same force on both sides. Usually one side drops in first and the other side is still in the air.

I think lubrication which does not bind dust should work. I ordered two types from Sydney. With Covid-19 it will probably take at least one week to get to the west coast.

Thanks and best regards
Tom Hunter

 

[bqt]

Not sure what you are doing if you are leaving skin on adjacent boards, but it don't sound right.
First of all, these boards were a bitch to insert 35 years ago as well, so it's nothing new.
If you have a quad board in a wider backplane, I usually am doing a bit of wiggling both when inserting and removing. The boards should have handles, and that is what you grab, so the skin should be safe.
If you have a hex board in a hex box, you normally have arms at the edges which works like levers. The really important thing here is to wiggle and work, when inserting, so that the board is truly in the correct place before using the arms to push it down into place. Removing means just lifting the arms, and are pretty painless.
With qbus, it's similar, except there quad cards are the wide ones with arms, and dual heights are the ones that need some wiggle. But when you're down to single or dual height cards, they are usually not causing that much trouble.
From a skin-scraping point of view, the worst might be the small Unibus grant cards, which you really need to reach down beside other cards to insert/remove. That can hurt some...

 

[bqt]

I realize that since this might have been more Omnibus-specific.
In the 8/E, I certainly find there is plenty of space for wiggling. And there I can grab the boards that don't have any handles by the sides. I've not had any skin scraping issues that I can recall in general.
The 8/A is hex wide, and have hex boards with the levers. Same observations as for Unibus boards apply. Quad cards are again easy to wiggle as needed.
But big cards are always a bit more work to get in/out. It hasn't really changed anything with age.
And I would also argue against applying any lubrication. With time, they all seem to collect dust and whatnot, and turn into goo.
It's a bit of work to get cards in/out, but it's not too bad.