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Old 6th Apr 2022, 10:39 pm   #1
SiriusHardware
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Default Spectrum 128+2 (Grey) musings.

This Sinclair (Amstrad) machine brought to a close my long love affair with Sinclair computers going back to the MK14 in 1978 - I bought this one probably in 1986 - still has the WH Smith price tag on it, £149, and I used it for perhaps a year before the Atari ST arrived on the scene. I never really loved this machine in the way that I had the original Sinclair machines, in part because it wasn't really a Sinclair - even the 48K mode start up prompt had been changed to say '@ 1982 Amstrad'. So for decades this machine has been in its box, largely ignored. When I did feel like getting a Spectrum out, it was always my original, real Sinclair 48K Spectrum.

However a recent thread over on the VCFED forums managed to revive my interest in this machine. There was a suggestion / revelation that three transistors had been fitted the wrong way around in all of these at the point of manufacture. I felt that was impossible because as far as I could remember mine had always worked fine and it had never been apart. As it turns out those three transistors, TR4, TR5, TR7, all 2N3904s, really had been fitted 180 degrees out. It looked as though the screen printing had been laid out for a typical BCxxx pinout but the 2N3904 has its pinout running the other way, so in order to orient these transistors as shown in the circuit diagram they do indeed have to be turned through 180 degrees.

Having sorted that, I then decided to replace the cassette deck belts (widely available as a kit of two) and also make up a new RGB video lead, my original one having been dismantled or repurposed at some point. Having got that working I am bound to say that the picture on my RGB CRT monitor is orders of magnitude better than the one obtained via RF-out or via composite - you would expect it would be better, but this is considerably better. The keyboard is also a lot nicer than I originally gave it credit for and so although this, like all 'enhanced' versions of original mainstream computers was relatively poorly served by any software taking advantage of the enhancements, I would say the ergonomic improvements alone are reason enough to choose one of these over the original 48K machine.

They are not without their quirks, though. Amstrad, in a deeply cynical move, rewired the two joystick ports so that they did not match standard Atari-type joystick wiring which was an almost universally observed wiring standard for switched joysticks. The idea was to force you to buy the proprietary 'Sinclair' SJS1 joysticks. Virtually overnight, adaptor cables appeared with a black socket on one end and a grey plug on the other so you could use your favourite joystick, or just the one you already had, with the +2. Before long joysticks appeared which had two plugs on the end of their cable, one grey for your grey Spectrum, one black for everything else.

Also, for reasons even they probably didn't understand, Amstrad decided to use what looked like a BT telephone socket for the RS232 / Midi interface socket instead of the ubiquitous DB9 which had been used on Sinclair's original Interface 1. Moreover, you couldn't plug a standard BT type plug into it, not without filing bits off the plug to allow it to be inserted. I presume Amstrad did this because they meant to be the only supplier of anything which could be plugged into these sockets, as with the joysticks.

I've looked around at work where we have a few products with telephone sockets edge mounted on the PCB and the footprint of those sockets appears identical to the ones used in the +2, the difference between them being that the ones we have at work DO accept a standard modular BT phone plug - so I am considering replacing Amstrad's weird non-standard ones with a couple of those. The only problem is that the original Amstrad sockets are black and the potential replacements are white, otherwise this would be a nearly undetectable improvement.

I thought the information about the wrongly installed 2N3904s would be of interest at least - this is the first I have heard of it myself.
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Old 6th Apr 2022, 11:15 pm   #2
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Default Re: Spectrum 128+2 (Grey) musings.

I remember GEC using a 'differently keyed' bt431 style black plug on a handheld programmer, these were available from one of the mainline component suppliers, I can't remember which or what they were called (useless I know).
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Old 6th Apr 2022, 11:21 pm   #3
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Default Re: Spectrum 128+2 (Grey) musings.

We had (long obsolete) units at work which used a left-handed (mirror imaged) version of the BT431 type plug and matching socket. I still have quite a few of the left handed plugs somewhere. Someone on the 'net' sells a Spectrum +2 to DB9 RS232 cable which just plugs straight in, so they presumably do know where to get the slightly weird ones which fit. I think the QL also used the same ill-chosen connector - not sure as I have never seen the rear connections on a QL.
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Old 7th Apr 2022, 5:04 am   #4
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Default Re: Spectrum 128+2 (Grey) musings.

The RS232 connector (also used on the QL)is/was a standard part. They were always black (to distinguish them from the white telephone plugs) and were, indeed, designed so you couldn't plug them into a telephone socket or plug a telephone cable into the RS232 socket. I've come across them on all sorts of bits of hardware, certainly not Sinclair or Amstrad specific

They are called the Plug 631W if the catch is on the same side as the normal telephone plug. (Plug 630W is the mirror image version, the QL used one type for the serial ports, the other for the joystick ports).

The good news, if you can get the plug, is that the normal crimp tool used for telephone plugs will do that one too.
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Old 7th Apr 2022, 8:34 am   #5
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Default Re: Spectrum 128+2 (Grey) musings.

That's very useful info! Thanks Tony.

Edit: And here they are. First supplier found when looking. Amazing the difference knowing the part number makes.

https://www.betterbox.co.uk/products...ug-ct6310.html

Last edited by SiriusHardware; 7th Apr 2022 at 8:40 am.
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Old 7th Apr 2022, 8:50 am   #6
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Default Re: Spectrum 128+2 (Grey) musings.

So what is the difference in keying between the 631W above and a 631A (the six-pin version of the 431A)?
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Old 7th Apr 2022, 9:01 am   #7
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Default Re: Spectrum 128+2 (Grey) musings.

Thats a very interesting piece of information , never ever heard of that before today.
Mind you, i skipped the +2 and went straight to the +3 which i still have to this day although its probably not been turned on for about 10 years at least.
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Old 7th Apr 2022, 9:24 am   #8
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Default Re: Spectrum 128+2 (Grey) musings.

If you look at a 'normal' white 431 / 631 plug end-on (as though you are the socket it is about to be plugged into) there are two raised bumps on the non-contact side. The black plug doesn't have these, so they have to be removed (filed down) all the way back to the raised ridge which limits the depth to which the plug can be inserted, before the white plug will go easily into a socket intended for the black plug.

The sockets on the Grey Spectrum +2 are indeed 6-contact so if modifying a white plug for this use it needs to be a 631A rather than a 431A. However, it appears that the correct plug is still available so it's not really worth mucking about. Most people would be more likely to have 4-contact 431As to hand so if you are going to have to order a plug anyway, it might as well be a 631W instead of a 631A.
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Old 7th Apr 2022, 10:23 am   #9
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Default Re: Spectrum 128+2 (Grey) musings.

Thanks for satisfying my curiosity.
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Old 7th Apr 2022, 12:16 pm   #10
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Default Re: Spectrum 128+2 (Grey) musings.

Quote:
Originally Posted by Dave Moll View Post
So what is the difference in keying between the 631W above and a 631A (the six-pin version of the 431A)?
The 631A has the corner (opposite side to the locking clip, opposite face to the contacts) cut away as a 'square step' all the way along the body of the plug. The 631W has a groove all the way down the body a little bit further over. You could think of the 631A as a groove actually on the edge I guess.

I can't remember if the 430W and 431W officially existed. If they did they're the obvious 4 contact versions.
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Old 7th Apr 2022, 9:16 pm   #11
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Default Re: Spectrum 128+2 (Grey) musings.

I had a wider look around, and actually that company linked to in #5 seems to be the only current supplier of the 631W that I can find - unusually there is no M.O.Q. so I have ordered three which should be a lifetime's supply for me. I'll probably put one on the end of a bit of flat 6-way telephone cable and take the other end to a DB9. I don't see myself ever needing the 'keypad' provided for by the second similar socket on the Grey +2.

I did also find the same firm referenced in a QL thread, it appears they also stock the 630W (left handed) version which as Tony mentioned is used on some, not all of the similar sockets on the Sinclair QL.
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Old 7th Apr 2022, 9:55 pm   #12
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Default Re: Spectrum 128+2 (Grey) musings.

Another point worth mentioning, I said I changed the belts on the cassette deck, I very nearly lost a couple of parts in the process.

Removal and refitting of the large belt is simple as the whole belt path is exposed, you just take the old belt off and when you are ready, fit the new one.

The small belt is a slightly different matter, as there is a very small gap between the underside of the flywheel and a small white plastic cap or flange just below it - see the attached photo. The original small belt is unusually thin which makes it not too hard to get out through the gap, but the replacement belt in a kit will usually be the same thickness as the large belt, and not at all easy to push through the gap. That was the initial process I went through.

If you try to remove the small belt and install its replacement without removing the flywheel you can end up dislodging the white cap / flange which is a friction fit on the black pin or spike that it fits onto. The white flange's actual job is to hold the spring down onto the white cam below - the cam provides the latch on / latch off operation for the pause button.

If the cap / flange does come loose while you are trying to get the small belt in or out, it may fly out sideways immediately, or it may only get as far as the underside of the flywheel, and then it will shoot out soon as you lift the flywheel.

The best way to avoid this potential problem is to lift the flywheel at least partially out so that there is a big gap to get the small belt through without it getting caught on the white flange, this also allows you to see that the belt is correctly seated on the flywheel pulley before you drop it back in. To release the flywheel so you can pull it out a little, you have to remove the plastic 'circlip' from the spindle on the other side of the deck.
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Old 8th Apr 2022, 12:47 pm   #13
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Default Re: Spectrum 128+2 (Grey) musings.

Brings back fond memories of mine. At one stage I wanted a printer to work with mine and wired a serial port to the rear of mine. Only problem was that the driverchip did not like the output being disconnected and the 128 ( 2 or 3 ??, I always thought the 2A had a tape drive ,where the 3 had floppy) had to be shut down to reconnect the cable. I did have a word processor program working but in the end I resorted to a simple method of programing in basic.
If anyone is still interested in using Basic on a PC, I can recommend BASIN. I use it working out componant values ,but I wisk I still had the one I developed at college ( in Turbo Pascal) had the ability to select componant values depending on the tolerance level needed and suggest the nearest of the values needed.
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Old 8th Apr 2022, 1:30 pm   #14
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Default Re: Spectrum 128+2 (Grey) musings.

The '3' was the one with the built in 3" floppy drive. Of all the Spectrum incarnations that was probably the one best suited for 'serious' use like word processing with programs like TASWORD which defined their own small (40 column?) font. You could do quasi-productive things on an earlier Spectrum if you had a Microdrive or one of the third party equivalents - somebody even sold a real floppy drive + interface for the original Spectrum, but they were expensive.

I distinctly remember using the serial output on the Interface 1 to send printer output to my 'proper' dot matrix printer, a Panasonic KXP1081, and I used that setup as my 'proper' computer for things like correspondence for several years.

I love BASIC. While I have been messing around with this machine for the past week or so I have written various BASIC programs to test bits of it out and I have never once had to refer to the manual, it all came back to me so easily. I can't do that with Python, even though I have written some fairly long programs in that language - I still grind to a halt within a line or two while I go off onto the internet or trawl through older code to find the exact syntax for what I am trying to do.

On the Spectrum 128 +2 I really prefer the '128' mode BASIC editor which lets you type the code in conventionally, character by character, rather than the multi-key-shift shorthand employed by the 48K mode editor.

It took me a few seconds to remember that BASIC statements on the Spectrum were always in longhand so

Variable=1

is invalid but

LET Variable = 1

...is valid, and for IF statements the THEN keyword is also mandatory. I don't mind that at all, as longhand code is more 'English' and understandable.
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Old 8th Apr 2022, 1:34 pm   #15
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Default Re: Spectrum 128+2 (Grey) musings.

Not been commenting, but it's all very interesting reading. It reminded me, I have a grey +2 packed away somewhere, as well as lots of other old computers, parts and accessories. I really should thin this stuff out a bit.
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Old 8th Apr 2022, 3:16 pm   #16
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Default Re: Spectrum 128+2 (Grey) musings.

First dibs if you do. No, no, I mustn't...
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Old 8th Apr 2022, 4:17 pm   #17
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Quote:
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First dibs if you do. No, no, I mustn't...
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Old 8th Apr 2022, 10:19 pm   #18
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Default Re: Spectrum 128+2 (Grey) musings.

#14 -Siriuus i got my wrist slapped at college using BASIC terms when programing in TB Pascal. Things like "WHEN IF " and other BASIC statements were definately frowned on.
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Old 9th Apr 2022, 8:50 pm   #19
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Default Re: Spectrum 128+2 (Grey) musings.

Brief update, my 631W plugs arrived and I can see by looking carefully that these are definitely the right plugs. They don't go into the sockets yet because they haven't yet been crimped onto a cable so the contacts are standing out a lot further than they will once they have been crushed into place.

My thanks to Kevin for recalling the possibility of the existence of a 'proper' plug to fit these odd sockets on the +2 and to Tony for confirming it and supplying the actual part number.
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