Restoring an old computer + neat trick for prototypers - Page 1
Forum section: electronics / projects

author: ataradov
author_rank: Super Contributor
timestamp: January 16, 2016, 10:19:24 pm
content: 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 languageNow 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.

author: amyk
author_rank: Super Contributor
timestamp: January 16, 2016, 11:41:31 pm
content: I recognise that wire - used widely in Soviet military/avionics. It's called?.

author: ataradov
author_rank: Super Contributor
timestamp: January 16, 2016, 11:44:36 pm
content: Quote from: amyk on January 16, 2016, 11:41:31 pmYep. 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.

author: dom0
author_rank: Super Contributor
timestamp: January 17, 2016, 12:02:22 am
content: ?,?,?,? = PTFE?

author: ataradov
author_rank: Super Contributor
timestamp: January 17, 2016, 12:05:45 am
content: Quote from: dom0 on January 17, 2016, 12:02:22 amSoviet name for this type of wire is  - 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

author: firehopper
author_rank: Frequent Contributor
timestamp: January 17, 2016, 12:07:04 am
content: it looks like wire wrap wire

author: ataradov
author_rank: Super Contributor
timestamp: January 17, 2016, 12:08:18 am
content: Quote from: firehopper on January 17, 2016, 12:07:04 amBut 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.

author: CM800
author_rank: Frequent Contributor
timestamp: January 17, 2016, 12:41:23 am
content: 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.

author: MLXXXp
author_rank: Frequent Contributor
timestamp: January 17, 2016, 01:25:10 am
content: Quote from: ataradov on January 17, 2016, 12:08:18 amKynar 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.

author: firehopper
author_rank: Frequent Contributor
timestamp: January 17, 2016, 02:27:42 am
content: could it be litz wire maybe?

author: ataradov
author_rank: Super Contributor
timestamp: January 17, 2016, 02:36:09 am
content: Quote from: firehopper on January 17, 2016, 02:27:42 amNope. All strands are connected and are there for flexibility and reliability.

author: Gyro
author_rank: Super Contributor
timestamp: January 17, 2016, 09:57:16 am
content: 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

author: Simon
author_rank: Unknown
timestamp: January 17, 2016, 08:54:17 pm
content: 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.

author: Cubdriver
author_rank: Unknown
timestamp: January 18, 2016, 06:15:35 am
content: Tefzel (ETFE) insulation, perhaps?-Pat

author: westfw
author_rank: Super Contributor
timestamp: January 18, 2016, 07:35:35 am
content: 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!

author: Simon
author_rank: Unknown
timestamp: January 18, 2016, 07:54:41 am
content: 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.

author: TerraHertz
author_rank: Super Contributor
timestamp: January 18, 2016, 12:26:04 pm
content: 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.htmIf 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.

author: ataradov
author_rank: Super Contributor
timestamp: January 18, 2016, 04:43:34 pm
content: Quote from: TerraHertz on January 18, 2016, 12:26:04 pmThat'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.

author: Gyro
author_rank: Super Contributor
timestamp: January 18, 2016, 07:23:57 pm
content: Quote from: TerraHertz on January 18, 2016, 12:26:04 pmOuch! 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.

author: TerraHertz
author_rank: Super Contributor
timestamp: January 19, 2016, 12:29:14 am
content: Quote from: Gyro on January 18, 2016, 07:23:57 pmI 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.Quote from: ataradov on January 16, 2016, 10:19:24 pmFOCAL - that's one I'd never heard of. Googled 'FOCAL programming language'. Plenty of hits.http://retro.hansotten.nl/uploads/6502docs/kimfocalug.pdfSo, it's very similar in style to BASIC?

author: ataradov
author_rank: Super Contributor
timestamp: January 19, 2016, 12:49:56 am
content: Quote from: TerraHertz on January 19, 2016, 12:29:14 amBASIC 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.

author: amyk
author_rank: Super Contributor
timestamp: January 19, 2016, 11:46:25 am
content: 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.

author: davebb
author_rank: Frequent Contributor
timestamp: January 19, 2016, 02:55:44 pm
content: 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

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 19, 2016, 03:44:07 pm
content: 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

author: Siwastaja
author_rank: Super Contributor
timestamp: January 19, 2016, 06:30:13 pm
content: Quote from: MLXXXp on January 17, 2016, 01:25:10 amMy 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.

author: TerraHertz
author_rank: Super Contributor
timestamp: January 20, 2016, 01:52:46 am
content: Quote from: T3sl4co1l on January 19, 2016, 03:44:07 pmSame as my search results.I do know for sure this wire was associated with Australia's FA-18 fighter planes. Or rather a test system used to service part of the avionics, but which probably used the same wire as in the planes. Manufacturer was Hughes.Just now it occurred to me to look at freshly cut ends of the wire strands under a microscope, and interestingly there's definitely no copper core under what I thought was silver plating. It's bright silvery all the way through. Wow. I think this is pure silver wire.Wish I had a camera on this microscope to show pics.Hmm, now I'll have to dig out a long length of it, work out the cross section, and see what the resistance is vs should be for silver.QuotePaywalls to the horizon. Also, very likely to be nothing there due to very limited use and being military.I still have plenty of it, if by chance some means to analyze the insulation turned up. But I think it's going to remain a mystery.Quote from: amyk on January 19, 2016, 11:46:25 amWhatever it was, it was a small trace amount on the wire surface. It took a lot of wire handling to produce that effect. Also it was definitely the substance itself that produced the slippery feeling, rather than saponification of skin tissue due to a base. Affected fingertips felt the same as the wire itself, and it would not wash off with water, detergent, industrial hand cleaner, solvents like turps, metho, etc.

author: LukeW
author_rank: Frequent Contributor
timestamp: January 20, 2016, 02:59:29 am
content: Any recommendations for relatively cheap PTFE-insulated hookup wire in smallish (not a whole reel) volumes? Or is hunting around eBay for surplus avionics the best bet?

author: KL27x
author_rank: Super Contributor
timestamp: January 20, 2016, 03:18:03 am
content: QuoteLook for "silver plated" in the description. I have bought from the same seller for many years, and the wire tins, instantly. I buy it by the 1000 foot roll, and it's good from start to finish, many years later.I have also tried to use 30AWG solid core PTFE wire, but I found it's a bit of a pain to strip. The insulation flows through the blades of a wire stripper. Kynar is my go-to, but I can see using Teflon where you need the high temperature protection.I tried using some multistranded wire, but the connections were mechanically very weak. I highly prefer single strand solid wire for pcb intraconnects and only preferentially use stranded for large gauge connections where the two ends are NOT fixed in relation to another, using crimp or strain relief. For intraconnects on the same board, I find solid core is much less prone to fatigue breakage. AND you can route it better. Stranded wire has a natural form which it doesn't lose, so the wires pop away from the board in arcs, which is the other half of the reason it is prone to breakage, IME.

author: SL4P
author_rank: Super Contributor
timestamp: January 20, 2016, 03:29:35 am
content: Is the slippery residue perhaps a silicon film ?That will be initially resistant to water & washing - and may have been added to the outer insulation aid in lacing and looming of the original assemblies...

author: TerraHertz
author_rank: Super Contributor
timestamp: January 20, 2016, 04:48:51 am
content: Quote from: KL27x on January 20, 2016, 03:18:03 amI second this. Pic is a 1000 foot roll of kynar single core silver-plated wire I bought at least 30 years ago. It still solders perfectly well. The board is something made with that wire.Quote from: SL4P on January 20, 2016, 03:29:35 amDon't think it's a silicon compound. I commonly get assorted silicon oils/sprays/greases on my fingers, and never had any such reaction. Also it doesn't seem possible to wipe it off that wire. It stays slippery. I assume it's some additive to the teflon to improve abrasion resistance.

author: helius
author_rank: Super Contributor
timestamp: January 20, 2016, 05:49:52 am
content: ETFE decomposes to hydrofluoric acid, which is initially painless but causes very severe and lasting problems.

author: RobertBG
author_rank: Regular Contributor
timestamp: January 20, 2016, 07:21:49 am
content: Quote from: helius on January 20, 2016, 05:49:52 amThe second I read the symptoms this was my first thought.I dont know if the stuff breaking down turns back into HF but it is one of the things used to make teflon. I have been around HF enough to know the dangers,it is EXTREMELY nasty stuff and by the time you realize it major irreversible damage can be done.Lets not to mention how deadly HF can be.It basically burns from the inside out and will kill off your skin,it's not your usual acid burn.Like I said I dont know if it will breakdown into HF but I'd be damned sure that it isn't because by the time you realize it the damage is done and it is TOO late with HF.During training they showed us a case where a guy got HF splashed on 8% of his body and even with immediate help and treatment he died several days later.........it's that scary

author: IconicPCB
author_rank: Super Contributor
timestamp: January 20, 2016, 08:13:16 am
content: Teflon decomposes at 1200C to the best of my recollection

author: BradC
author_rank: Super Contributor
timestamp: January 20, 2016, 09:26:43 am
content: Quote from: IconicPCB on January 20, 2016, 08:13:16 amIt starts failing at 260C and decomposes at 350C. Decomposition products are not particularly nice, but not nearly as bad as HF.