Making Tape Great

Finally, I managed to get around to testing the cassette recorders with a working ZX Spectrum. (Note that all this playing was done with the minimum of repair work - there are separate posts coming on what I fixed (or didn't)...)

Unnecessary Spectrum Pic

But. I didn't have any mono cables. I tried a stereo one and found that it was, to be blunt, useless. A stereo jack has a connector made of three metal sections. The one at the tip that enters the socket first (no sniggering at the back) is left audio, the one in the middle is right audio and the sleeve at the bottom is ground. For 3.5mm mono the tip is audio and the sleeve is ground.

In all the cassette recorders I have the 'ear' sockets are constructed so that the mechanism that holds the plug in place makes contact with the tip and sleeve for ground as expected.  But the point at which the ground connection on the plug varies. As a result, the cassette recorder might make contact with the tip and ground sleeve but the Spectrum at the other end has contact with the tip and centre ring i.e. no direct connection.

To get around this I came up with a (bad) idea. Take an existing stereo jack to jack lead and join the sleeve and centre ring together at one end. I won't bore you with the details but it was a little bit successful and a lot not very good. It did work and resulted in my getting one of the cassette recorders to load my game but with an additional blob of solder on the plug I was concerned I would damage the sockets. So I abandoned that idea and ordered some cables from eBay. 

A fine example of what not to do..

That's better..

Now I have all the right equipment it's time to get going. Here's the setup I'll be using, a 48K issue 2 ZX Spectrum with a composite mod. The TV is a 6 inch Sony Trinitron kindly donated to me by one of my most excellent work colleagues. I shall be trying to load 'Flight Simulator' by Psion. It should take about four minutes and consists of a very small initial program load, followed by a loading screen and then the main program.

Watched over by Baby Yoda.

So, there are actually six machines that I have and I have listed the results of my shenanigans below:

Sanyo M787G

This one couldn't be tested. It's sadly not working. I do have the service manual for it and I am hopeful that I will be able to get it back up and running again. Watch this space.

Sanyo DR-101

This is the most modern of the recorders I have (if they can ever be called 'modern'). It's also the most slimline and the lightest.

Load that sucker!

Looks promising..

This unit has a switch on the side labelled 'Normal' and 'Data'. I started in the 'Data' position and it actually failed the first time. 

..spoke too soon.

This was a slightly disappointing start to say the least. I switched it to 'Normal' and tried again. Volume was at maximum and it still sounded very quiet through the Speccy speaker. But it worked.

Load time : 3 minutes 57 seconds

Philips D6310

This one was basically a big pile of plastic bits for a long time. Following the 'great reconstruction', thanks to the supply of new cogs from my awesome brother, it now works - or at least it plays cassettes. It's very noisy but it could just need some lubrication in the right places. Not so sure about whether it will load Speccy games.

It's a beast.

First attempt, well it didn't go well. It did get as far as the loading screen but the bottom third was the wrong colour and once it finished that block I was presented with the infamous 'R tape loading error' (again).

So close, but so far...

Second attempt, re-seat cable and reduce volume very slightly. And...even worse. It didn't even get to the screen before the tape loading error message made another appearance.

Our situation has not improved.

Load time : FAILED

Bush (no model number)

Note the 'Rank Organisation' Logo

I had high hopes for this one and I wasn't disappointed. Well, not as much as for the D6310. This one has a handy 'tone' control along with the volume and I set them as you can see in the picture, volume about 9 and tone about 8. 

I'll give it this, it loaded the game without any problem at all. The only fly in the ointment was the loud clanking from the mechanism as it played. I could remove it completely by gently applying pressure to the 'STOP' button so there is obviously something out of alignment inside. And the rewind refused to work too. Some work required on this one then. But at least it loaded!

Load time : 3 minutes 53 seconds

WH Smith CPD8300

A mighty machine

This is another beast and the only one that came with its own plug attached. It has a 'monitor' switch too so I could listen to the cassette output at a decent volume from the speaker. On the back is also a selector switch that could be either 'Spectrum' or 'Other'. What is it about the Spectrum?!

What else is there, except 'Spectrum'?

No problems loading with this one. The only thing is that the 'monitor' function could really do with a reduction in volume. I had to put my hand over the speaker, the bloody thing was so loud! I did try again with the monitor switch to 'off' and it worked fine too - and was much quieter.

I did have some problems with this one randomly stopping but I put that down to the tape being wound too tight (thanks to the Bush machine). A quick fast-forward and rewind sorted that out.

Load time : 4 minutes 9 seconds

York Radio Cassette

I hit an unexpected snag with this one. The audio out was a DIN socket and I couldn't find a headphone socket...

No 3.5mm socket? Sad face. :(

So, after all that, I only managed to get four machines of six machines actually tested and, of those, only three would actually load the game. The biggest disappointment to me was the Philips as I put many hours into getting the bag 'o bits back into something sensible. There are still some tweaks I can do it so all is not lost with that one.

I was very interested to see the difference in loading times. Over four minutes for the WH Smith unit just confirms what I thought in that it runs much slower than the others. 

Loading from tape is archaic and very, very slow and error prone. But those noises whisked me straight back to the front room of my Mum and Dad's house in 1984. Happy days. :)

The Most Challenging Composite Mod - In the WORLD. (Maybe not..)

A short interlude before I start playing with cassette recorders..

My Acorn electron is still waiting for some more attention, mostly because I don't have the correct cable to load cassettes and I don't have the 'retro' budget to splash out on the available SD card type options. 

An Electron walks into a bar...

But one thing I hadn't realised was that the composite output is actually monochrome. I was quite surprised at this as I knew I'd seen videos of people using their electrons with gloriously garish colour through composite. Well, it turns out a fact well known to Electron aficionados is that there is a very, very simple mod that can be made to change the monochrome output to colour. This was completely unknown to me, of course, but here's the proof, direct from the Electron service manual:

So, according to this, all I need to do is bridge the link labelled 'LK4' and it will add the chrominance component to the composite output i.e. monochrome becomes colour.

Time to break out the screwdrivers.

Electron bottom...

Gratuitous Action Shot

Under the hood.

With the motherboard completely removed from the case I just needed to find LK4. It wasn't too hard to find.

LK4, whereart thou?

Gotcha!

With the link located I decided to take a leaf out of Mark Fixes Stuff's book and, instead of just soldering a link across it I would add a couple of header pins to allow a jumper to take it back to monochrome i.e. it would be reversible.  After a bit of scrabbling around in the spares box I liberated a four pin header from an old Sky box motherboard and proceeded to snap it into two two pin headers.

First soldering job was to clear the two holes of the existing solder. This was easy enough with a dab of flux and some solder wick. Surprisingly, the hardest bit was soldering the pin header to the board. Holding the pins in place with my finger resulted in several minutes of inappropriate language as the rapid transfer of heat through the pin, fully complying with the expected laws of thermodynamics, burned my bloody finger. 

Trying to hold the pins with pliers proved tricky to say the least. After another minute or two of appalling profanity I manged to get one leg holding on by the merest sliver of solder. This was enough to allow me to solder the other leg and then finish the job. It's not the straightest but it's only got to hold a jumper. Annoyingly, that transistor (see below) made it tricky to get one on. A firm push of the transistor moved it a sufficient amount to remove that problem..

Lovely jumper.

But did it work? After re-assembling the case and doing all the screws up I realised I hadn't taken any pictures of the Electron in monochrome, so no Before and After pics. But here's the evidence that my traumatising injury (slightly burnt fingertip) was worth the agony (mild irritation).

Colours. (Ignore the reflected bald head.)

And now, back to those pesky cassette recorders. (Well, soon anyway.)

A Catalogue of woe...

After looking over my unexpectedly large collection of cassette recorders, I decided it was finally time to test which ones would be suitable for use with the faithful old Speccy. There are a couple of reasons. First, I like things to be original where the can be - although I'll never shy away from a faster loading mechanism if it's a good price - and second, if they work with the Speccy then there's a good chance they'll also work with my recently acquired Electron (as long as I can get a cable).

So, down to business, I went and pulled my Spectrum+ out of the box upstairs where it had been stored for the last eight months or so. Main unit? Check. Power supply? Check. Smart Card V2 from Retroleum? Check.

And then, the first problem. Powering up I was greeted by the happy beep of the Smart Card but I couldn't move the cursor up and down to select a game. How odd. I switched off, removed the SC and powered back up. Much to my disappointment and annoyance a large proportion of the keys had stopped working. This should not have been a surprise since it was still the original membrane but I had spent a long time 'tuning' the keyboard to keep it going and it was actually 100% working when I put it away. Sadly, the tails are now too far gone and it's game over for this membrane.

Tails, tails, tails

I hate this keyboard

But no problem. I already have a new membrane that I bought a while ago. It's been sat in a drawer for about a year. Out it came. BUT. This one has corrosion on the tails too! What. The. Heck. For some reason, this membrane is suffering the same fate as the original despite only being a year or two old. I put it into the Speccy to see whether I might be lucky. I wasn't. Almost the same amount of keys just did not work.

Corrosion on modern membrane

Look at the two outer tracks
Brown, not gold..

At this point it was time to give up on the Spectrum + so I removed the Z80A and re-installed it back into the CPC that it had originally came from. See the results of that, here.

Plan B. Get the 48K rubber keyed Speccy out of storage and use that. So, out it came. It's an Issue 2 but we won't hold that against him. The 3D printed case I have for my Smart Card V2 (as provided by my awesome brother) lifts the rear of a standard 48K case off the desk, but that's fine. It's only for testing stuff and it's fairly stable anyway.

Turn it on. Oh, for fudges sake. It won't boot. It's stuck on a black screen with a white border which screams of a RAM issue. So I switch the SCv2 to Diag mode. But this also struggles to boot although, fortunately, this was just down to a dirty edge connector (we've all been there!). A quick rub down with some IPA and cotton buds and the diagnostic ROM boots successfully..

Dangnabit.

...and promptly identifies IC 18 as suspect. 

Curse you IC18!

So out comes the de-solder station.... 

I have a distinct Hal feeling.

Anyway, the de-solder station makes light work of the suspect RAM IC. In a few minutes it's removed and a socket installed in it's place. 

Heath-Robinson RAM Tester

But this is a good excuse to get my RAM tester out of the drawer and check that it actually IS the problem. And sure enough, the RAM tester says it's fine. Wait? What?

That was unexpected. The RAM tester thinks this chip is OK but if I put it back in the Speccy I just get a black screen. Something is clearly affecting the result. But that's for another day. For now, let's just get a new RAM chip in the socket and see if it will boot. And then I realised the only RAM I had is a couple of chips of the infamous 'MT' variety. Known for being crap, but I had no other choice and it would only be for a few minutes of testing. Urgh, I feel dirty putting this chip in there but, sorry buddy, it's only for a short time. In fact, I was so embarrassed about having to use these pariahs that I didn't even take a photo of it. 

But does it now work? Yes, yes it does. :)

Testing, testing.

Annnnd, we're back in the room.

There is no way that I'd ever leave one of those MT chips in there so I needed to find a solution. Fortunately I had a stash of Sanyo 33256 chips which came from an old and decidedly broken A501 512Kb Amiga expansion. The pinout for these chips is virtually the same although they have a higher memory capacity, and consequently an extra address line at Pin 1. I thought long and hard about whether I should try to use one of these. Eventually, my ancient, addled brain decided that I could either pull Pin 1 out of the socket or connect it to ground and it should work. And would you believe, pin 1 on the upper RAM chips is connected to ground by default.

The only other difference was pin 9 which is A7 on general RAM chips of this type but is labelled as 'AR' on the Speccy. Basically, the original chips in the spectrum were specifically chosen as they had a fault on one bank of 32K of their 64K. As a result, Sinclair apparently got them cheaper but it means that the original chips have to match which bank is faulty. In this case, it's irrelevant as the chip is fully working with 64K (well, 256K really). It just means the Spectrum will only use one half (or quarter) of the chip. 

Here goes:

Sanyo to the rescue

Yay! It works!

Boo! The picture is, to coin a phrase, complete garbage. It's difficult to convey how back the picture really was on this thing. Imagine the worst RF output you can, then make it a bit fuzzy, lose all colour (except a big smear of dark blue across the whole screen) and you'd be somewhere close.

Sadly, this is an Issue 2 which has a deserved reputation for this due to it having manual picture controls. Later revisions had an automatic circuit built in so the variable resistors next to the ULA (pic above) are not in there from Issue 3 onwards.

Fortunately I have a shiny new sillyscope - which is actually a generous donation from my Boss. Let's see what we can see.

Composite TV signal ahoy!

So the big dips are the 'back-porch' which tell the TV, "I'm about to start a new field'. Then the squiggle to the right of the dip is the colourburst. As the name suggests, this contains the colour information for the field. Finally, there's the main part of the field. Compare this to the display at the time:

Bad colour. Smudgy. Urgh.

To improve this the variable resistors need to be tweaked to get the video signal as 'flat' as possible. This is easiest with just the white boot screen, rather than the busy screen I had up. Once I took out the SmartCard and booted up to a plain white screen, it was much easier to see the fuzzy nature of the signal.

There is a very, very narrow sweet spot for VR1 and VR2. Once it's there, it's great. You can see the result on the sillyscope below:

Ahh, that sweet spot!

That's better.

So, now I have a working ZX Spectrum with RAM fixed, clear(ish) picture and a queue of cassette recorders to try.

Except, I don't have any mono audio cables...

FFFFFUUUUU...

Next time, I butcher a stereo audio cable and finally get a cassette to load into this Speccy (preview image below!).

Ah, the nostalgia for those raster bars..