PCBs for Spectrum Clones

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Bill B
Posts: 237
Joined: 26 Jan 2014 16:31

PCBs for Spectrum Clones

Post by Bill B » 25 Jan 2020 12:46

Probably prompted by my struggles with making my own PCBs, Lez as gifted me with three professionally made PCBs:
  • ZX Max 48
  • Superfo Harlequin 128
  • Superfo Harlequin +3
Since I am stubborn and determined to build my own design, I thought I would pass at least a couple of these boards on to others.

Note that these are bare boards only. If I have any relevant chips amongst those I have received from Lez I will include them, but mostly you will have to source your own components.

Send me a PM if you are interested in having one of these boards.

Martin A
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Joined: 09 Nov 2013 21:03

Re: PCBs for Spectrum Clones

Post by Martin A » 01 Feb 2020 12:16

So, I took Bill up on the offer of a Spectrum clone PCB. I know he want's some updates, so I've posted a couple of pictures. :D

While I wait for the rest of the parts to arrive in post from the US, I've started on the keyboard.

I used the 48k spectrum as a guide, since there's no way to duplicate the "key and shift" double keypress of the 128 and later Spectrums with the key-switches I have to hand. Sinclair seem to have used a 20mm spacing, so the matrix board's best fit of 8 holes is 20.32mm is close enough. The depth of the board is sufficient to put the space in it's proper place. I thought about duplicating the shift keys on both sides, but decided on the end to just double them up to make them wider, but keep the original positions.
Checking the key spacing
Checking the key spacing
keyboard mockup.jpg (97.08 KiB) Viewed 915 times
The keys are now all in place, waiting for some wiring, but this is how it fits over the PCB. I used slightly longer than required posts to make sure there's clearance for the cables that will connect the keyboard, and the AY-3-8910 to 8912 adaptor board I'll also need to squeeze in between the boards to get the sound working.
Test monted of the PCB
Test monted of the PCB
Mounted.jpg (90.94 KiB) Viewed 915 times
PS Have you seen the cost of the AD724JR AD converter chip ? It's more than the Z80, a lot more!

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Dave
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Re: PCBs for Spectrum Clones

Post by Dave » 01 Feb 2020 13:22

AD724JR SOP-16, £1.44 from China in singles, less for 5 or 10 pieces

regards
Dave

Bill B
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Re: PCBs for Spectrum Clones

Post by Bill B » 01 Feb 2020 14:13

And since it is the RGB to NTSC/PAL Encoder, do you need it?

If you have a monitor with RGB input, then you could just leave it out.

Martin A
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Re: PCBs for Spectrum Clones

Post by Martin A » 01 Feb 2020 14:49

Nothing slow enough to sync to the Spectrum's RGB output except the TV via SCART, and 8 pin mini din to SCART isn't exactly common... (I will fit the mini din socket just in case.)

Composite on the other hand I've a range of displays from the 30+ year old V7001 to a 4" reversing camera screen.

Fitting the AD724 seems to be the way to go.

Martin A
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Joined: 09 Nov 2013 21:03

Re: PCBs for Spectrum Clones

Post by Martin A » 07 Feb 2020 00:21

The package from the Mouser in the US arrived today, so no I can add more than just empty sockets to the board.
The bits have arrived.jpg
The bits have arrived.jpg (87.83 KiB) Viewed 876 times
I fitted the AD724 first, getting to those pins once the surrounding parts are fixed would be awkward in the extreme.

I then fitted all the other sockets and started on the passives, it's going to take a while. One wrinkle, the board's designed to use a real Spectrum PSU and unlike just about every cheap PSU from China, it's negative centre.

Luckily I have a spare of the real thing, but that something to be aware of for whoever builds the other boards.
More than just sockets fixed.jpg
More than just sockets fixed.jpg (137.14 KiB) Viewed 876 times

Martin A
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Re: PCBs for Spectrum Clones

Post by Martin A » 08 Feb 2020 23:50

I think (I hope!) that's all the soldering done, I'll do some basic tests tomorrow and then start populating the ICs.
all soldering done I hope.jpg
all soldering done I hope.jpg (145.97 KiB) Viewed 861 times

Martin A
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Re: PCBs for Spectrum Clones

Post by Martin A » 09 Feb 2020 18:27

It's built, I had nothing better to do while sheltering inside from storm Ciara, so I've finished the Harlequin 128 build.

Here's the board with everything except the rom added
just the rom to add.jpg
just the rom to add.jpg (116.83 KiB) Viewed 851 times
Now with the rom fitted and the keyboard mounted
completed.jpg
completed.jpg (90.44 KiB) Viewed 851 times
The 512k flash has room for 8 different setups, I have used 4
Spectrum 48k original
Spectrum 48k Gosh Wonderful
Spectrum 128k
Spectrum +2/3

Here it is running the last of those
it lives.jpg
it lives.jpg (33.54 KiB) Viewed 851 times
And with the required "Hello World" program input, the keyboard seems to be responding perfectly.
Keyboard test passed.jpg
Keyboard test passed.jpg (28.35 KiB) Viewed 851 times
There's a slight amount of jitter that shows up on the TV, for example on the sides of the blue bar on the loader screen. I think that could be the TV and not the board, as they didn't show un on the initial test on the old composite monitor.

The last thing that needs to be completed is the adapter board to fit the AY-3-8910, then of course some more involved "testing" once I find the tape deck.

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1024MAK
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Location: Looking forward to summer, in Somerset, UK

Re: PCBs for Spectrum Clones

Post by 1024MAK » 09 Feb 2020 23:00

👍 :D

Mark

Bill B
Posts: 237
Joined: 26 Jan 2014 16:31

Re: PCBs for Spectrum Clones

Post by Bill B » 10 Feb 2020 11:33

I knew it would not take you long :D

Lez will be pleased that at least one of the boards he supplied has been put to use.

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