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Brad’s 2-5-2-2 Perfect PCB Toner Transfer Process

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When I got started with making my own printed circuit boards (PCBs), I found a plethora of ways and methods. However, very few seemed to work properly. Toner transfer seemed the most straightforward, with several companies offering special papers designed to make the process easy. But these were expensive, and the results were not nearly as good as promised.

The best toner transfer method seemed to be the old toner transfer-to-magazine paper trick, but I always ended up with a few missing traces in the end. However, after doing some experimentation, I discovered a ‘process’ that seems to yield the right result almost every time! I call it my 2-5-2-2 Perfect PCB Toner Transfer Process. Here it is.

Print your PCB Artwork

This is the easy bit. Assuming your artwork is all to scale (and reversed – don’t forget if you don’t mirror image your artwork, when you iron it it will appear backwards). You simply print it from something like photoshop to a decent laser printer. I use an HP LaserJet 4250. The toner itself seems to be a point of contention, with some saying the compatible toners don’t work. However mine has a compatible cart and works fine.

Carefully tear out a piece of magazine paper from a… magazine. You want something glossy but not too glossy. I pull out the regular pages from HotRod Magazine. Their paper is really good quality. Plus, I can read about awesome car projects I’ll never be able to afford!

When printing, the crucial thing is to make sure the printer knows what type of paper it’s handling. I use Photoshop, so in the printer settings I tell it the paper is heavy glossy. This causes the printer to do two things: 1) draw from the manual feed tray and 2) pull at a slower speed so more toner affixes to the page. You want this because you want the toner to be solid and not too thin, otherwise it won’t protect your traces from the etchant properly.

Once printed, you’re ready to prep your copper clad.

Prepping the Copper Clad

This is very important. Copper needs to be slightly roughed up for your toner to get a good grip on it. I use a Scotchbrite pad and some Comet, dry, not wet and I scrub at it like crazy for at least a minute, everywhere I can in random patterns. I then rinse in fairly warm water until clean. Next, I wipe the board down with some paper towel and acetone.

Ironing

This is the bit that always trips people up. Many recommend ditching the iron for a laminator. But if you don’t have the money to dish out on fancy new equipment, an iron (you don’t care about) will do just fine. It’s all about technique, heat, and pressure. First, set your iron to the hottest setting (usually cotton). Do not set it for steam. You don’t want steam at all here.

Next, put your copper clad on your work surface (in my case, it was a kitchen counter) with the copper side up. Place a piece of parchment paper over it. Set a timer for 2 minutes and begin moving the iron slowly back and forth, up and down, all over the board to get it nice and hot.

The reason I use parchment is because I found magazine paper/ink will melt and become gummy, binding on your iron. Over time, this will wear off the non-stick coating on the iron surface. The parchment paper reduces friction considerably.

When your timer goes off after 2 minutes, remove the iron and parchment paper.

Now you’re ready to align your magazine paper with the artwork printed on it. Align it over the board and do not let the magazine paper touch the board until you have centered or aligned properly. The second it makes contact with the hot copper, it’ll stick.

Bring the magazine paper gently onto the copper clad surface. Now place your parchment paper over it.

Set your timer for 5 minutes and start ironing the whole of the magazine paper underneath. What I do here is a few ‘sweeps’ from side to side, sort of ‘laminator like’. Slow and with lots of pressure. Then I imagine in my mind’s eye where the traces and pads are and give a fair bit of pressure (not too much) and put a bit of extra pressure on the tip of the iron to get all those places pressed down nicely. I also do a lot of light sweeps back and forth, up and down all over the place to get the heat nice and even.

When your timer goes off after 5 minutes, remove the iron and set it aside. Leave everything else as is.

Set your timer for 2 minutes, and walk away. I honestly do not know why but this ‘cooling process’ seems to help. While giving it a rest, fill a sink or bucket with cold water. This is what the PCB will be dunked into once we’re done.

When your timer goes off after 2 minutes, set it for another 2 minutes. Take your iron and again repeat what you did for the previous 5 minutes. Really work the iron one more time along where traces, pads, etc will be.

When your timer goes off after 2 minutes, remove the iron, put on an oven mitt. Remove the parchment paper, then grab the board. The paper should be firmly stuck to it. Dunk it directly into your sink. Let it sit for a good couple minutes. The longer it sits, the more the water will break down the fibers of the paper and make it easier to separate from the board and toner. Gently peel the paper away, following the directions of traces where possible.

Voila! A nice, crisp transfer! And no need to spend money on fancy blue stuff!

Now you can trim off the excess, and proceed to your favourite etching method. I will discuss mine in a future post.

Mark-8 Clone Project

… Or maybe it’s not that easy

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Okay so let’s start with what I had to do to make some period correct looking Mark-8 PCBs.

One thing I’ve had to learn the hard way with the toner transfer PCB-making process, is that it really relies on good quality artwork.  If you’re working third-hand with someone’s low quality scan of original artwork, you’re going to have a problem.

While initially my first attempts at making a double sided Mark-8 CPU board looked successful, when I examined the finished product more closely with the eyes of experience from my TVT project, I realized it wasn’t.  Looking closely at the traces, I could see a ‘pixelated’ pattern which I think was a result of the dithering from the low resolution, greyscale scan I had been working with.

Some months after I made that first board, I came across an auction for an original TV Typewriter.  I lost, but the seller, a generous fellow named Roy, offered to send me a ‘consolation prize’ in the form of an original Mark-8 construction guide!  Having an original booklet in my hands meant I could experiment and try to get the best possible scan quality, with an eye towards making new boards rather than just archiving history for others to read.  I would try to get the traces as dark and thick as possible, to better accomodate my  “ironclad” toner transfer procress.

The first thing I did (carefully) was fool around with my guide and my day-to-day Brother all in one scanner.  However, the scanner’s top end resolution is only about 600dpi, and I was finding it was distorting the artwork dimensionally.

I then remembered that I had a much, much better scanner tucked away in a closet.   This was a professional photo scanner, given to me by a late client of mine.  It is a Microtek i900, an older scanner but with a still-impressive 6400×3200 resolution capability.  The resolution in particular is fantastic – I’ve actually been able to scan stills from 8mm film and get pictures out of them!

Microtek gives you a pretty nice interface software-wise.  I am setting this to a strict black and white line art mode.  Getting the traces perfectly black is very important.  Greyscale printing at less than 100% black means you run the risk of having thin traces.  I want my Laserjet 4250 to paint those traces on nice and thick.  I also want to have pure black and white (line art mode, to the scanner) so that there is no in between anywhere I don’t want toner – no ‘grey’ patches that will resist my etchant, leaving me with unsightly splotches or bridged traces.

To really make sure I get it all, I set the scanner to 1200dpi.  It takes a couple of  minutes at that resolution to get it all in, but the result is fantastic – crisp and clear with no fuzziness:

I decided to print it off on an overhead transparency sheet to compare it to the original.  To my amazement, there is no distortion whatsoever.  The scanner rendered a perfect copy!  Yahoo!

Now I need to clean these up and prep them for transfer to copper.  One thing I will take the opportunity to do here is put some pin holes in the IC pads.  This will make drilling easier.  I’m doing this all one one side, and only in a few places on the other.  It’d be difficult to get all the holes lined up properly so I’m sort of saving some energy here.  I’ll simply drill from the side with all the hokes, and then use the few I’ve made on the other side for aligning both boards.  I’ll also flip them so that they come out the right way when ironed on.

Just as I did with my first attempt, I need to use Photoshop to get the two sides nicely aligned with one another so that when they are produced as a board, there won’t be any pads or holes out of place.  I made a good call in checking this, rather than trusting that if my transparencies matched the plans, all would be ok.  As it turns out, the two sides for each board in the plans do not always align!  I don’t know if this is printing errors, or the effects of 45 years of humidity changes, but they definitely do not.  So here’s photoshop at work again.  Basically what I do is temporarily convert the images to grayscale (this allows me to create layers).  I then copy one side of the board I’m working on and paste it over top of the other.  I then scale back the opacity on the new ‘layer’, such that I can see through it somewhat.  This’ll let me get them lined up.  For the actual line up process, I’m using a variety of Photoshop tools including scale and warp.

With that squared away, I move on to toner transferring and etching.  First I print them off on my Laserjet 4250 on the ‘super glossy’ setting, which prints nicely on magazine paper (and slowly).  As I’ve mentioned before, I use my totally unpatented 2-5-2-2 process to get a nice crisp image from my iron.  It really helps that my printer lays on the traces nice and thick solid black here.  What a help that is.

When I’ve got both sides for a board ready, I trim them with my scoring tool, and then dip them in my vinegar/salt/peroxide bath.  I’m still feeling my way around with this process but I’m learning that it’s better not  to apply the salt directly on the copper.  It actually can cause pitting and even will peel the toner resist away from the board, which wrecks your traces.   Another thing that can happen: put too much salt in and it will cause a very strong reaction with can discolour the PCB substrate with an ugly yellow/green.   To avoid all that, I pour the salt in alongside the board and then just sort of swish the etchant tub back and forth gently.  I set the whole thing in a sink of hot water to help the reaction along.  Anyway, it’s a slow process but it seems to leave the PCB unscathed.

Now here’s the hard part – gluing the two sides together.  I thought this would be easy – just paint some epoxy on both sides, press em together and…

Meh.  I mean, it’s functional — the epoxy works, but I’m left with these ugly splotches, like the one on the lower right in the photo.  What I find out the hard way is, the epoxy is almost impossible to brush to a consistent level across both boards.  This produces spots of varying sizes and darkness when you press them together, which do not look period correct or correct at all.  I’m trying to make these boards look like they were original single piece double sided boards.  That is not what we are getting here.

I’ve got to think about this now and try to figure out how to make this work.  Some have suggested getting a book press to clamp the boards tightly and squeeze all the air out.  But that’s another expense for something I won’t use that often, and book presses are pricey as well as heavy!  Hmm.   I think before I go that route, I’m going to have a look at other adhesives…

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TV Typewriter Redux Redo

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When we last left off, I had found, to my great excitement, some actual vintage 1973 PCB copper clad stock.  And I was delighted; this gave me the opportunity to go the ‘last mile’ in authenticity.  It meant my TV Typewriter would be composed approximately 95% of vintage parts!

Of course, this presented a problem.  Since I had gone ahead and built my TVT with the new board stock, it would mean (ugh) taking it all apart and redoing it on new boards.  I really wasn’t keen on starting over again.  It was really tempting to just finish it off and carry on.  But events forced my hand.

The first was my acquisition of a vintage, original TV Typewriter construction booklet!!   This was the guide Radio Electronics would mail you for a fiver.  It had a reprint of the original article, as well as schematics and, crucially, the full size PCB layouts!

It’s quite amazing to have one of these in my hands!

You’ll recall to create my TVT boards I had relied on scans of the plans on SWTPC.com.  These were very useful, but unfortunately the scan quality was not great.  And these were afflicted with another problem: scanner distortion.   The original artwork was printed at full size in the construction guide, and since the writers didn’t expect as yet unborn children to be relying on scanned copies, there was no scale provided.  I did my best to scale it up, measuring against actual ICs.  I figured if I got the IC pad spacings right, the rest would fall into place.  I was wrong.  I had noticed as I built that some things seemed a little cramped.  But again, with only photos or scans to rely on, I had no way of being sure my dimensions were out.  However, now with the originals guide in hand I could compare.

I had thought I’d be out by maybe a quarter inch or less.  In fact, I was out by a full half inch all the way around.  This was confirmed by the arrival of my brand new one-off Signal 24-1A transformer, which Signal Transformer themselves had resurrected for me.  Looks pretty sharp, eh?

Buuut… it doesn’t fit.  The transformer actually cuts into the area where the three other boards plug in.  Ugh.

Another thing which I had neglected to do was read the instructions.  For this, I had no excuse – they were there in black and white in the scans on SWTPC.com.  The manual warned specifically to proceed in stages, but as I was a bit too eager to get going, I had built the boards completely out of order and simply as parts arrived.  This was a mistake.  The order of construction is just as important as anything else; by proceeding in a specific order one step at a time, you are able to isolate potential problems as you go.  This is invaluable.

Thus the decision is made: I must re-do.  De-soldering will be painful, but a valuable lesson has been learned.  And anyway, I can at least get that last squeeze of authenticity out.

 

Mark-8 Clone Project

Mark-8 board do-over

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As I mentioned in a previous blog post, I got lucky and came across a whole bunch of vintage, produced-in-1973 Synthane Taylor boards.  The production date codes were 1973, as verified by the still unopened bags they were in:

Pretty amazing that these had sat unused all these years.  And as mentioned, they bear the same little ‘Tc’ marks on the PCB substrate that the originals do (albeit different colour):

Previously I had posted that I thought these were the marks of Techniques, the company that produced the original kit boards back in 1974.  I have since determined that Tc actually stands for Taylorclad.  Techniques, I believe, did not make the substrate or blank copper clad stock that was ultimately used for the kit boards – they were just contracted to lay them out, etch, tin and package them for buyers.

In other blog posts I’ve mentioned my disappointment, as someone who desires a replica that is as close to original as possible, with modern PCB stock.  It just doesn’t look right, which is obvious in photos.  Again, compare an original Mark-8 board (right) to one I produced on modern copper clad stock (left):

It might not be immediately obvious to the untrained eye, but it’s definitely something I notice.  So I’m grateful these boards have been available.  The fact that they are only 0.030″ thick vs. the standard thickness of 0.060″ actually works to my advantage; I can simply make one side of the two sides, then the other, on two separate sheets, and then bond them together….

Adventures in Vintage Computing

Vintage PCB stock found!

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I can’t believe it!

Working on various vintage reproduction projects, an irritant has been the look of the modern PCB stock we have available today.  Modern PCB stock is made with a different process compared to decades ago and as a result both the color and texture are different enough to make it a dead giveaway that your reproduction is just that.   Not that we should try to deceive – we do have a responsibility to ensure that future collectors are not fooled.  But for my own purposes, especially for projects where the boards will be visible, that modern stock just ruins the whole aesthetic.  Here’s what I’m talking about:

On the left is a new Mark-8 PCB produced using current PCB material.  On the right is an original Mark-8 board fabbed using the old process.  You can see there is a distinct difference in color – a kind of ‘fluorescence’ to the vintage board on the right.  Further, when you get up close and look at the new board, the product is very smooth – vintage stock had a grain to it that was very apparent.   No amount of dye or other tricks can correct this.  Further, vintage PCB stock often has manufacturer ‘stamping’ on it that identifies where it was produced.  My Mark-8 boards have NVF or Tc stamped all over them – indicating in the latter case that they were made by New Jersey fabhouse Techniques.

Unfortunately for years, the stuff on the left was the best I could do.  Until two weeks ago, that is.  I had been constantly searching ebay for ‘vintage PCB’ or ‘vintage copper clad’, the former yielding nothing and the latter yielding pots and pans.  However, one day I decided to try searching via Google.  I don’t know why but Google often finds things ebay itself can’t find.  To my amazement, up came an auction for vintage PCB stock!  And not just unknown vintage either!  Actual dated stock from 1973!!!!!

I couldn’t believe my eyes.  I know this seems like a trivial thing but to me this is huge.  With actual 1973 board stock, I can make something that is virtually indistinguishable from the original!  Naturally I ordered everything the guy had.  Two weeks later, here it was:

Incredible!  I mean, I’d expected to find something vintage-ish with enough searching.  But actual new-in-bag with verifiable date of production?  Crazy!!  These boards have survived untouched since the days of President Nixon.  They were around for the last days of the Vietnam War, Watergate, the fall of the Soviet Union.. wow!  There can’t be too many of these still lying around out there, but I’m glad I kept the faith that there had to be at least some!

The boards are 0.03″ thick, rather than the usual 0.06″.  But actually, that’s okay.  Because they are single sided, if I wanted to make a Mark-8 board, which is double-sided, I can just make the two sides separately and then laminate them together.  I’ve made boards from double sided 0.06″ stock.. it’s tricky.

I am currently working on building a SWTPC PPG joystick.  I had already made one from the modern PCB stock – let’s see what it looks like with vintage!  I almost feel kinda guilty opening these packages that have been untouched for four decades…

I used the usual toner transfer process to get my resist pattern onto the board.  It went down pretty much the same as with modern – however, perhaps owing to the thinness of the substrate, the iron did manage to melt a sort of checkerboard pattern into part of it.   Whoops!  Anyway, next I cut it (easy, since it’s only 0.03″ thick!) and etch.  Here are the results.  First, we’ll compare it to my modern board stock:

Note: I etched a second piece of the vintage stock completely so I could sandwich it to the first piece, to give an idea of the color with the board at 0.06″ thickness.  Above is the result, below is a TVT board I made using modern stock.  Interestingly the scanner kind of distorts the color a bit, but you can still see a difference.  In real life, the modern board is a more brown/yellow color and stands out pretty dramatically vs. the vintage board stock.

Here is a scan of the joystick board next to an original Mark-8 board:

Bit of a difference in darkness for sure.  In person, the Mark-8 board doesn’t look that dark and in fact looks much closer to the NOS vintage stock.  And it should, since they both were made by Techniques.  Know how I know?  Check it out:

That, my friends, is Techniques’ mark.  Same marks that appear on my original Mark-8 boards!  Different color — the ones on my Mark-8 boards are kind of red, but still.. very cool!  I can make brand new Mark-8 boards that nonetheless have the old Tc stampings on them!!

Anyway, the lesson here is patience and persistence pay off.  I knew it had to be out there and just kept looking, for years.  There is probably more, maybe even some double-sided or 0.06″ thickness.  It’s definitely out there!  Now I’m in a pickle.. do I leave my TVT as it is or go the last mile and remake the boards from vintage stock?  Hmmmm… 🙂

 

 

TV Typewriter Redux

Printing Silkscreen Layer with Ghost White Toner!

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Well it finally arrived:

As you know, printers do not print white typically, they work subtractively and simply don’t put toner where white is required. Essentially with this Ghost White Toner, you remove the black toner and install the white. You continue to print whatever you’re printing as ‘black’, the printer thinks its black but really it comes out white. The toners are made by a company called Ghost White Toner in Germany. They claim to offer white remanned toner for several models, however I found in practice they really only had one available for the HP Color LaserJet Pro 200.

I went this route because for my TV Typewriter boards,  I wanted them to look as close to the originals as possible. I could have just printed in black for the silkscreen side, but that didn’t look prototypical to me. I also looked into actual silkscreening, and there is a company that will take your design and make it into a silkscreen. But then ya gotta buy the screen, the paint, deal with the mess.. blah. I just wanted to print it off and transfer. That’s it – not mess around with paint.  I knew, peripherally, that there were printers out there that printed white – used for transfers to tshirts, etc. But they were $3000! I thought about using my toner remanufacturing skills to just buy the white toner powder and refill a black cart with it, but even a bag of the powder was at least $300. Then I found these guys.

So let’s see how it prints to my magazine paper transfer medium:

Looking at it, it looks kinda thin. But that could also be because it’s white and maybe not as opaque as other colors. Let’s fire up the iron and one of my TVT spare boards and see what happens.

I didn’t try very hard – this board is a scrap unit I can’t use because it was etched wrong.. so I didn’t really work it with the iron. But, you get the idea. It’s not bad. But it is thin. I’m reading the instructions and it appears there are some adjustments to print settings you can make to print it darker. I’m going to try some of those next and see how they work out. It may also be partly the magazine paper I’m using.. perhaps I need to use actual transfer paper?

But yeah, a lot easier than actual silkscreening, and in white, no less! The toner itself cost $115USD + shipping – not completely out of line for a toner. Ghost White will sell you a complete kit with appropriate printer for a few hundred bucks. I bought my LaserJet 200 on ebay for $49. Works great, although I had to do some repairs because the shipping monkeys broke it.

Anyway, pretty pleased. Will keep trying different settings and let you know how close I can get.

TV Typewriter Redux

Nearing completion

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This week I put in my order to Signal Tranformer for a new 24-1A transformer.  Believe it or not, despite the passage of 40 years, Signal will still custom make just about anything they previously made, for a price.  The cost of the transformer itself is about $103USD – not cheap, but according to Signal it will be identical in every way to the originals used in the 70s, which would be handy since the TVT instructions call for a 24-1A as the preferred unit.

The boards meanwhile are pretty much done.  Here they are (please forgive the lighting:

And stacked together:

TV Typewriter

Now I just have to hope that when I apply power, it works.  I should note that I kind of failed to follow the instructions – the instructions have you build the unit in a particular order in order to safely test things as you go.  For example, the instructions for the mainframe have you build and test the power supply before installing other components like the RF modulator.  This is to minimize the risk of serious damage if something is wired wrong.    I could help myself perhaps by dismantling those parts.. but I think with a good, thorough checkover (several times) I’ll feel pretty confident about plugging in the mainframe at least and working my way up.  Cannot believe I’m so close to being finished!  What a fun ‘little’ project!

TV Typewriter Redux

Assembling the case

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The final pieces are on order and now I’m moving to assembling the TVT’s case.  For trial purposes, I built the first case out of fir and plywood.  I had initially thought plywood was correct – in pictures of the original it appeared to be plywood peeking out from the left side where the vinyl covering had peeled away.  I was wrong.  It was metal.  And indeed, if I’d read the manual all the way though I would have known that all along – the article strongly recommended using a metal case to prevent RF interference from the device, which is a no-no!

For the side pieces I went with red oak.  I kept looking at photos of the original and that seemed to be, in terms of grain, as close as I could get.   I even got a bit cheeky and made sure the right side had a knothole, similar to the prototype!

I then routered out the insides.  This wasn’t quite as hard the second time around, although I did accidentally cut a notch through the front of the right side.  Argh!  I’ll have to figure out a way to fix that.

The case is assembled with a piece of 5/4″ wood (yes, that’s what it’s called) for the front ‘palmrest’, and then the back is a piece of sheet metal from Canadian Tire.  One thing I learned for bending metal – you need a brake!  I thought it’d be easy enough to fashion the metal into a box shape with nice crisp corners.  Nope!  Turns out metal really resists corner shapes!  No matter how much force I put on it, I couldn’t do it.  I ended up using a ballpeen hammer and an edge to bang it more or less into shape.  Thank goodness it’ll be covered with vinyl!

 

Looking alright.  To hold it all together, I ended up using No More Nails.  That stuff is quite strong and was able to hold the metal in place.  To bond the vinyl to the metal top, I initially used the same but as you can see in the pictures, it developed serious wrinkles.  So, I ripped it off (I had lots of vinyl; a square yard can cover a lot of TVTs!), sanded down, and did it with contact cement.  Much better, no wrinkles!

The really tricky part of assembly was getting the keyboard to fit – when I first put it together, the return and space keys were binding on the case.  I had to router things out a bit more (hence the accidental notch).  I realized later my case dimensions were out by about 1/4″ of an inch.  Not noticeable visually, but enough to cause these sorts of assembly headaches.

Anyway, after the glue has set, we have a pretty good facsimile of the original.  Check it out – mine is up top (obviously) and the original is pictured at the museum below:

Not bad if I do say so myself!  So yeah, basically I need to find a way to fix that accidental notch, because I am not messing with the router again.  And then I need to get the legends and nameplate made up.  Probably Front Panel Express will be where I go to do that.  But for now, on to getting the main unit actually working!

TV Typewriter Redux

The Memory Board (Page A)

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Things are rolling along smoothly on my TV Typewriter build.  At last, I have reached the summit of this device – the Memory board.  This is the board – easily the most intricate and complex, and important.

The Memory board is where the magic happens.  It is host to the Signetics 2513 character generator ROM:

Chances are if you had any involvement with 8 bit computing back in the day, you’ve had or used this ROM.  It was used in the Apple I, the Apple II, the SWTPC CT-1024, early Atari games and so on for generating (upper case) text.   In fact, if you’re typing on an original Apple II, you’re producing exactly the same characters this TVT device does.

The memory board also hosts the all important ‘memory’, in the form of 6 Signetics 2524v shift registers.

These tiny (and rare) 8 pin chips can each handle 512 bits of information.  If my calculations are correct, 6 of them together produces the equivalent of about 384 bytes of memory.  Oooooooh!

Now, the TVT was a modular design, so you could add additional ‘pages’ of memory to handle more.  But to get to just 1KB you’d need three of these things, and because my prototype case is only about 4.5″ tall, it wouldn’t fit.  So I’m sticking with just the one – that’s good enough for a full page of characters.  Plus, it’s not like Page B will do you much good.  The two pages do not exist seamlessly for the user – ie, you can’t just type two pages worth of data on the screen, scrolling down as you go.  You have to manually flip a switch to go between pages.  When you reach the bottom of either page, the whole thing blanks and begins fresh.  Anything you typed before is gone!  As a terminal, this is pretty useless.  Don was questioned back in the day on the design by Lee Felsenstein, and his response was essentially ‘hey buddy, it’s for putting words on a TV screen!’.

And at any rate, supposing you did make use of both pages, dutifully typing out your 2 page essay on your TVT.  You had no way to back it up, unless you knew how to wire up a cassette recorder.  Or here’s another recommended method from the article:

LOL

Well, I guess technically it is a hard copy..

Again, Don Lancaster’s TV Typewriter is not an entirely practical device out of the box, really.  It was about the concept.  Further development was up to you (or him), depending on who got to it first.

Anyway, the Page A board is distinct from any subsequent boards you build – Page B etc don’t need to have their own character generator or associated circuitry, so a whole bunch of resistors, etc are left out.  But for Page A, it’s all on, and this board is a blizzard of ICs, resistors, diodes, caps and my least favourite thing in the universe next to mint-flavoured-anything: jumper wires.  Lots.  And lots.  (And lots).  Lots of jumper wires.  You need to be in a Zen mode to handle that.

And you need to pay very close attention.  Because the traces are tightly packed, there’s a lot of holes, and it’s easy enough to accidentally bridge something with solder or install into the wrong holes.  Definitely do not do this while tired!

The drilling was the worst though – it took me about an hour with a Dremel to get it all and even my poor eyes, which were crossing, missed a couple.  And let me tell you about drilling PCBs: it stinks.  Do not do this in a small room.  You should also wear a respirator.  Drilling PCBs produces a nasty, smelly, very fine glass dust.  It’ll stink up your room for an hour.  Trust me.  Do this in a garage.

Anyway, after that and about about five hours of soldering, here’s what we have so far:

Looking pretty good!   I received and am using those little Bakelite 100uf caps.  They definitely look period correct!  I’m also mixing and matching the other IC sockets as I suspect any hobbyist/prototype maker reaching into his parts bin would have back in the day.

I am waiting for a correct-looking 24 pin socket for the character generator and some blue 8 pin sockets I found for the shift registers to finish that end of it off.  In the meantime, I’ll Zen-out and install jumpers everywhere else it’s needed.

Regarding connecting all four boards together,  I’m relieved to report that they all can be snapped together, with a fair bit of finagling.  In this pic I haven’t pressed them in all the way – I really hate Molex connectors and the amount of force required to install or separate things with them.  It flexes the hell out of the boards and makes me cringe every time.  I’m amazed the pins are breaking off!

Anyway, here’s a beauty shot.  Beneath it is a shot of Don’s original.  We’re getting there!

TV Typewriter Redux

The RF modulator

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Probably the most important circuit on this whole device is its RF modulator.  The RF modulator takes is essentially a ‘converter’ that takes a pure video signal and emits it at a frequency a television receiver can pick up.   As has been explained to me by folks more knowledgeable than I, the RF modulator is essentially a  Hartley LC circuit.

In the TV Typewriter, a coil of solid wire is fed current to produce oscillations at a frequency your television set can intercept and interpret.  There is a 33pf trimmer capacitor installed alongside that allows you to precisely trim the signal.  For example, if I wanted the system to use channel 2, I’d need to adjust until I was putting out signal at 55.25mhz.

Setting out on the project, I had been advised by both contemporary and historical sources not to bother with the modulator and instead just pipe video direct to composite monitor to make it easy on myself.

However to me, the whole point of a ‘TV Typewriter’ is its interface with a TV.  Sure, you could have bought a monitor back in the day, but monitors were expensive.  The genius behind the TV Typewriter was the realization that most people already had a perfectly good ‘monitor’ in their home – their TV!  To build the TVT without a TV interface just seemed pointless.  After all, I already have a TVT-2 that does direct composite output.

Probably I will come to regret this decision later.  I did run into some snags trying to make my coil.  The article advised I needed to take a 4″ piece of solid 14 gauge wire, and twist it 6 turns on a 3/8″ mandrill, spacing the turns so that the whole coil is about 1″ long.  Well, here’s how many twists I was able to get with 4″:

Hmm.  I decided to write Don directly about this.  This wouldn’t be the first error encountered in the directions.  I asked him if I could go longer and what the implications would be.  He said no problem (‘shouldn’t be critical’ were his words) and gave me some pointers on what I was shooting for frequency wise.

I ended up taking a 7″ long piece of wire and got my 6 turns out of that.  With that all shaped up properly, I then turned my attention to how to fix it to the mainframe.  Obviously I can’t direct solder the ends as they have to pass through to the copper traces on the opposite side of where the coil is mounted.  I couldn’t see clearly enough in any pictures of originals I had if they had used special mounts, so for the ends I just soldered in two solid wire ‘posts’ and then soldered the coil ends to that.

That seemed straightforward enough, but I was at a loss as to what to do about a third connection implied by the drill pattern on the PCB:

The instructions, being written for people who actually knew what they were doing, did not explain.  Was that another mount point?  If so, why?

This is where it helps to read schematics.  The schematic is specific that you must ‘tap’ (attach) a third point to the coil on the first turn:

Why?  Not being an electronics expert (yet), I can only hazard a guess that current is passed from one end of the coil to the other, and the third ‘tap’ is placed at a point where sufficient signal/oscillation is generated to be usable.

The trace the third tap is on leads directly to the 300ohm twinlead, which is a flat ribbon-like cable those of us over a certain age might call ‘antenna cable’.  You can see it on Roy’s unit here – it’s long and flat and has two little ‘Y’ connectors that screw into the TV’s VHF antenna terminals at the back:

 

This is more or less the TVT’s antenna, carrying signal from the unit to the TV to intercept at your chosen channel.  As I said before, a lot of TVT builders ran aground on this particular rock.  Bob Rethemeyer ran into this particular problem when he built his – the output was apparently terrible.  Apparently it requires a lot of fidgeting to get working properly, and that’s why so many chose to just direct the feed to composite monitors or gave up entirely.

Anyway, here’s the circuit more or less completely installed:

Personally I think RF output will be the least of my problems getting this thing to actually run.  But, we shall see!