Spectrum 48k power jack
 

Hi all

I picked up a Spectrum 48k at the weekend.

For reasons not yet understood, a past owner has run the power supply into a metal box with an on/off switch and then the wire from that is soldered into the computer. I intend to remove this and return it to a more normal state.

Can anyone tell me the correct dimensions for the jack plug (which must be long gone)? Also, any suggestions for a 'good' one?

Martin

Re: Spectrum 48k power jack
 

6th item down on this page.

https://www.retroleum.co.uk/spectrum-connectors

I have used the seller, who specialises in retro computer parts, myself, but I have not bought this particular part before so I can not comment on its quality.

I don't know if you were also asking about the needed dimensions for the matching plug - according to the link above the 'hollow' in the DC plug needs to be 2.1mm diameter (as opposed to 2.5mm which is the other common size). Be aware that it is connected centre NEGATIVE and the original PSU was 9VDC (unregulated) and 1.4A current rated.

The Spectrum doesn't have an on-off switch or a reset switch so the only way to reset it is to pull out the power and plug it back in again, which potentially causes a lot of wear and tear on the power socket and plug, and maybe that was what caused the demise of the original socket, now no longer present. The 'flying' on-off switch will have been the original owner's solution to this problem.

Re: Spectrum 48k power jack
 

The socket is still present - the wire must be soldered to the underside somehow. Its the plug thats gone. I wonder if that went kaput through wear and tear.

I may buy a new socket and jack plug while I am at it. That looks like a good site.

Re: Spectrum 48k power jack
 

Looking in the description in Retroleum, it appears to be a standard 5.5/2.1mm power connector (the measurements being socket and pin diameters respectively). These are widely available.

I agree, though, that the site looks useful for the more obscure items.

Re: Spectrum 48k power jack
 

I would say that the inner cable cores almost certainly fractured just at the point where the cables entered the strain relief on the original plug. The original plug was a moulded item so it would not be possible to do the usual shorten-and-refit with the original plug.

I think my own Spectrum's original PSU has had its whole DC power cable replaced at least once, with another cable with a moulded plug taken from a redundant wall-wart. Unlike more modern PSUs the spectrum PSU can be taken apart (screws underneath the stick-on felt feet) so it is easy to replace the whole cable.

Re: Spectrum 48k power jack
 

I have opened up the switch box, which I thought was something from an old project as it has three "things" incorporated it in. I presumed only the switch was being used.

Turns out there is an on/off switch, a bulb, and what I am guessing is some sort of "reset" button to temporarily cut the power. They are all wired up.

Before I dismantle it, is there an advantage to keeping this arrangement in place? I know its purpose, but it doesn't look elegant :)

I haven't powered the Spectrum up yet as I've not had time to do it properly.

Re: Spectrum 48k power jack
 

If you want to keep it, put a Spectrum compatible 2.1mm panel mount power socket on the box and take a short (3"-4") flying lead out of the box and put a 2.1mm plug on the end of that, then you can either choose to plug the Spectrum PSU into the 'box' and plug the short lead from the box into the Spectrum, or just plug the Spectrum PSU directly into the Spectrum, leaving out the box.

As said, from the sound of it this just sounds like it is an externally mounted off switch, possibly in series with a push to break switch which to all intents functions like a reset switch as it momentarily removes power from the system. The bulb / led? will be a power-on indicator, presumably. The 'features' in the box will be intended to allow the power plug at the Spectrum end to remain plugged in, reducing wear and tear on the plug and socket.

Re: Spectrum 48k power jack
 

Thanks - I'd not thought of that. Making a guitar effect style unit that can be included, or not included, might be fun actually.

Of course the big question is whether the computer works. I hope it does - I was given one years ago and ended up binning it, so this seems like a second chance.

Re: Spectrum 48k power jack
 

The only 'hard' part on a Spectrum is the ULA chip, which may or may not be getting hard to find now.

The ribbon cables from the keyboard membrane to the connectors on the PCB may have gone brittle so they might crack and start distintegrating, but even they have been recently remanufactured and are available, as is the screen printed aluminium keyboard overlay which, unless you are very careful, tends to get buckled when you try to lever it off to replace the keyboard membrane.

Re: Spectrum 48k power jack
 

I will proceed with caution. Ultimately I'd like to have a working computer for myself or, if I think it's too tough a job for me, pass it on to someone with the skill to get it running.

I used to have a 128k +2 - I wish I'd kept that one too :)

Re: Spectrum 48k power jack
 

Just a quick update on this.

I have now tried the computer and it "works" in so far as I get the '1982 Sinclair Research Ltd' screen.

None of the keys work so I have now sent off for a keyboard membrane from the supplier mentioned above. Presuming the keys work when that's installed I will be able to type the load command will I? I think I was expecting this copyright message to disappear after a few seconds.

I used to have a 128+2 and have hazy memories of the order in which things are done, and suspect it wasn't quite the same anyway.

The switch box thing I mention above works very well actually. Although it looks a bit Heath Robinson, it's a useful item. I may try to spray the box at some point and generally make it look a bit more official.

Anyway, the computer has now cost me more in parts than it cost to buy, so I am committed now :)

Martin

Re: Spectrum 48k power jack
 

I honestly can't remember if the copyright message does go away or if it stays there until the first time you hit a key.

With the keyboard disconnected, you should be able to 'type' something by momentarily joining row and column connections on the PCB mounted keyboard connector - but because of the radical input system used on the Spectrum, pressing individual keys that way will mostly make whole keywords appear.

Still, if that works it will give you some hope that the machine will work when it has a new membrane.

One thing you can try, since you have nothing to lose, is to cut about 1.5cm off the end of the original keyboard's ribbon cable and expose new 'ends' by cutting away the outer plastic layer and see if that makes it work. If it does you might be able to keep the original keyboard membrane for a while and hold the new one in reserve.

Re: Spectrum 48k power jack
 

Yes, the copyright message stays there, until the first key-press, that prints a character on screen (or results in a cursor symbol change) - So should be all keys apart from Shift? - And you should also hear a click from the speaker if the keypress results in a a character being printed.

Yes, you used to be able to keep shortening the keyboard tails a bit more, as they usually always fractured where the bent sharply at top of the socket, until they are finally too short to reach.
However, I once saw a way to overcome this, by a TV repair shop, whol desoldered the Keyboard connector from the PCB and glued it to the upper case, just where keyboard ribbon came out. So at least that would be unlikely to fail again, with no strain on it. They then soldered standard (0.05" pitch, although rarer double-spaced 0.1" pitch would be better) ribbon cable to this and to the main PCB. Although it would be better to use a proper 0.1" pitch plug&socket connector for ease of future servicing (Probably need a fairly low-height one, than usual 'Molex' KK 0.1" ones).

However, may well find that the original plastic on the membrane cables has now gone much more brittle and fragile after nearly 40years. I found the ones in a Sharp Microwave cracked by themselves in much less time, - Although they had bent them through 180degrees (and annoyingly glued cover layer over the silver paint and had the shape at the end change size, so making a repair rather difficult)