Restoring an old computer + neat trick for prototypers

[ataradov]

I'm working on restoring an old Russian (Soviet) computer back to life. Now that computer seems to be in working condition, I needed a way to load programs and games. Originally computer is supposed to load programs from a tape recorder. And tape recorder interface actually works, I tested it with MP3 player and embedded test program. But it is slow and inconvenient.

Additionally there is an interface for external devices. The interface simply exposes MCU bus directly. So I've created a device that connects to this bus and simulates ROM devices, selecting from a number of images stored on the SD card. The hardware is done, but software is not ready yet.

I'm also attaching an picture of one of the standard extension blocks. This one contains ROMs with tests and FOCAL programming language

Now to the trick part. As you can see, this thing is done on a prototyping board with wires. Those are teflon insulation wires. Teflon insulation does not melt under normal soldering temperatures, allowing for precise length control down to 5 mm (1/4"). If you do any prototyping work at all, get some of that wire. It is a bit more expensive, of course, but it is totally worth it. Forget the mess and frustration that melting PVC insulation creates.

The wire used here is from the same era as computer itself, so it is only available in pink (apparently Soviets did not know how to color it). Modern stuff is available in variety of colors.

[amyk]

I recognise that wire - used widely in Soviet military/avionics. It's called ?.

[ataradov]

It's called.

Yep. And not only avionics. Anything even remotely military or dual intent.

And not only Soviets. I recently bought some length of teflon wire scraped from US aircraft equipment. It was obviously salvaged (just as stated in the ebay auction) as it was in pieces 1 ft long. It was pretty cheap too, but a bit on a thick side for prototyping like this.

[dom0]

?,?,?,? = PTFE?

[ataradov]

PTFE?

Soviet name for this type of wire is [edited] - multi-strand flexible thermo-resistant with PTFE insulation.

Teflon is a DuPont brand name for PTFE.

EDIT: well, this forum does not like Russian language

[firehopper]

it looks like wire wrap wire

[ataradov]

it looks like wire wrap wire

But it is not. It is multi-strand and very flexible. And I've never seen wire wrap wire in teflon insulation, it just does not make any sense.

Edit: Here is a closeup view.

[CM800]

I've came across this exact wire taking apart some old UK Naval equipment from a DoD contractor on work experience. I wouldn't be surprised if it was PTFE. It looks beautiful when bundled and tied up neatly with black tying wire.

[MLXXXp]

it looks like wire wrap wire

But it is not.

Kynar insulated wire wrap wire does work well though. Kynar is quite tolerant of high temperatures and doesn't shrink back when soldered. I use it all the time for this purpose. However, the thicker, clear wires on the board below, at the top and right, are solid non-insulated wire with Teflon tubing on them.

[firehopper]

could it be litz wire maybe?

[ataradov]

could it be litz wire maybe?

Nope. All strands are connected and are there for flexibility and reliability.

[Gyro]

The thing you have to watch with stranded ptfe insulated wire is solder wicking up the strands under the insulation and causing it to easily fracture near the end under movement / vibration if you don't strain relieve it. I think it was Bob Pease who mentioned it in one of his articles.

Edit: Found it... https://books.google.co.uk/books?id=yLMgBQAAQBAJ&pg=PA62&lpg=PA62&dq=bob+pease+teflon+wicking&source=bl&ots=XG2OqKolbQ&sig=S5aJoS97cCsTBoUhJwGsV8Zz8gA&hl=en&sa=X&ved=0ahUKEwikobb2zLDKAhVG6xQKHVVcC6oQ6AEINDAD#v=onepage&q=bob%20pease%20teflon%20wicking&f=false

[Simon]

For military stuff we use double walled PTFE insulated wire, usually "raychem 44". Solder seeping up the strands and stiffening them causing them to break is why most connectors are now crimp terminals and ordering old 5015 connectors is a nightmare as you have to specify so many "special requirements" just to make the things acceptable to modern designs.

[Cubdriver]

Tefzel (ETFE) insulation, perhaps?

-Pat

[westfw]

Don't pull that PTFE around any sharp corners though, it "flows."
We had some old computers with wire-wrapped backplanes, and a primary failure mode was that one of the wires would end up shorting against a post that it had been pulled too tightly against - after a decade or so of tension and vibration, the post would just PUSH through the insulation.  I was a good thing we had a founder who had been in on the early days of that system, and was good at finding that sort of error!

[Simon]

PTFE is not the most flexible. rather than use a single 8AWG cable I use 4 16AWG ones twisted together as itmakes the whole thing much more flexible.

[TerraHertz]

Here's similar teflon insulated wire, but a bit thicker. This is from US military avionics.
And a cautionary tale about that wire. It's dangerous to handle: http://everist.org/NobLog/20100630_two_dummies.htm
If you have mil-avionics teflon insulated wire, and as you handle it your skin starts feeling 'slippery' and that feeling won't wash off with soap & water, stop handling it immediately.

It's too bad; it is very beautiful wire.

[ataradov]

Here's similar teflon insulated wire, but a bit thicker. This is from US military avionics.

That's the one I've got from Ebay. It is a bit too thick and stiff for prototyping like that. The Soviet one, even of the similar gage is way more flexible.

Also, that white teflon feels a bit differently under temperature, but I can't exactly pin point what is the difference.

[Gyro]

Here's similar teflon insulated wire, but a bit thicker. This is from US military avionics.
And a cautionary tale about that wire. It's dangerous to handle: http://everist.org/NobLog/20100630_two_dummies.htm
If you have mil-avionics teflon insulated wire, and as you handle it your skin starts feeling 'slippery' and that feeling won't wash off with soap & water, stop handling it immediately.

It's too bad; it is very beautiful wire.

Ouch! I wonder if the same applies to Molybdenum Disulphide grease, I tend to use that quite often.

Edit: Ah good, not according to what I've found on the web so far.

[TerraHertz]

Ouch! I wonder if the same applies to Molybdenum Disulphide grease, I tend to use that quite often.
Edit: Ah good, not according to what I've found on the web so far.

I wondered (and searched) the same. Molybdenum on its own doesn't seem to be particularly poisonous, nor the compounds found in common greases. So what is the form used in that wire that is so harmful? Can't find anything on the net. I'd really like to know. My toes are _still_ somewhat numb.

I'm also attaching an picture of one of the standard extension blocks. This one contains ROMs with tests and FOCAL programming language

FOCAL - that's one I'd never heard of.  Googled 'FOCAL programming language'. Plenty of hits.
 http://retro.hansotten.nl/uploads/6502docs/kimfocalug.pdf

So, it's very similar in style to BASIC?

 

[ataradov]

So, it's very similar in style to BASIC?

BASIC is much more user-friendly. FOCAL is easier to parse. The entire interpreter is 8 KB. BASIC interpreter is 16 KB for the same machine.

That computer is a reasonably close clone of PDP-11, so FOCAL was original default language. People hated it, so the next revision booted into BASIC and FOCAL was moved to that extension block.

[amyk]

I don't think it's C8/PFOA, since that is a "strong acid" and you would notice your skin dissolving rather quickly and painfully whereas what you describe sounds more like a base... it could be some other contaminant.

[davebb]

it could  be ETFE wire, as avionics do use ETFE as it does not give fume's if there is a fire, run your finger nail along it ptfe is harder your nail will slide over ptfe and with etfe there will be some grip.
Dave

[T3sl4co1l]

I don't see any articles relating teflon and dermatitis or toxicity (besides the usual toxic-byproducts-from-overheating-nonstick-pans stuff).

I suppose you'd have to search the med literature to get a better idea.

Tim

[Siwastaja]

it looks like wire wrap wire

But it is not.

Kynar insulated wire wrap wire does work well though.

My experience is that wire wrap wire is completely useless for this purpose. The Kynar insulation is good enough, but the solderability can be so poor that the solder doesn't flow at all even with added flux. Makes sense, because the wire is not meant to be soldered, so the coating of the wire is optimized for cold (pressure) welding; solderability is not designed in, so it's only matter of luck.

YMMV, of course; I'm sure some wire wrap wires solder just fine. But the two rolls I have used are practically unusable. So as a general advice, I would avoid it unless you happen to have some that you have tested to work fine.

From the insulation standpoint, Kynar is good enough alternative for PTFE. There are many others, too, that are good for this purpose. Practically almost anything else than PVC.