Harlequin 128k

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Joslyn Moreci

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Aug 3, 2024, 11:28:20 AM8/3/24

to lelampglimul

A brand-new RGB scart lead for the Harlequin 128k Sinclair Spectrum clone machine fitted with 8 pin mini-DIN video port. Connects simply and easily to any television with an RGB scart socket. With stereo audio input via 3.5mm jack plug.

Connects RGB video and audio from the Harlequin 128 computer to an RGB scart TV. Suitable only for the Harlequin 128, we have a Harlequin 48 RGB scart cable available. Connects to 8 pin mini-DIN RGB socket.

The harlequin boards are a series of ZX-Spectrum recreation boards created by Superfo (And now others) based on work done by Chris Smith for his book "The ZX Spectrum ULA" (Which is an excellent read if your technically inclined by the way [Linky] ) with the addition of a disableable Kempston interface (128K versions)

These are all implemented as discrete through-hole logic for the most part (With the exception of the Video Encoder IC AD724JR which needs to be done first as its a bit of an arse if your not used to Surface mount like me.

However, because all the parts are low power rather than a 30 year old ULA, it uses a switching regulator, and *DOESNT* use the rather shonky circuit to generate 12v, -12v and -5v which is known to go bad if you look at it wrong, Its a damn sight more reliable and less power hungry.

The board is the same layout as an original 48K Machine, so can fit in a 48K case in case of the original, although if you want to use SCART, you need to cut a small piece out of the back. The Video output is composite, but these days that's a lot more convenient than the original PAL RF.

Note that this board does NOT support ALLRAM mode, so booting something like CPM will not be possible, and if you implement a Floppy disk interface, DOS_BOOT will probably fail. This does not stop using the normal booting of the file "DISK" from your hard disk however.

As with the 48K version, its a lot more low powered than the original 128K board, and will fit in a 48k+ and 128K Toastrack case (Technically a rubber key 48K case as well, but that's a lot more difficult to use because the 128k roms expect the composite keys and its a pain in the arse to remember to use Caps-shift to negotiate the menus

Note, its likely that DOS_BOOT will always fail due to the lack of ALLRAM mode, but this will only be an issue if you have a Floppy disk interface AND some copy-protected +3 Disks to use with it. It will then fall back to trying to load "DISK" from the default drive, which does work.

If you have zero idea, then you won't even get a project off the ground. Have you ever done board design? Ever completed a project with an integrated microcontroller from start to finish (schematic, PCB design, fab, assembly, debug, etc)? There are too many variables for chipsets, board designs, I/O, etc. If you're just designing a single PCB, that will also carry a hefty price tag for the size and layers needed, 4 layer and at least baby-AT / micro-ATX size. Also, you're going to have to design your own schematics, unless you plan on doing a 1:1 copy of an exact replica board - which in and of itself is still very challenging to accomplish with even a small team of knowledgeable people working on it. You'll have to source parts that are no longer in production, or design all your own equivalents and have a microchip manufacturer make them. At that point, you might as well just buy a $20-$100 286/386/486/etc motherboard and call it a day since they are plentiful.

If you're thinking about a Sinclair ZX Spectrum, all the schematics are on the service manuals but it can't be remanufactured anymore. The main reason is the ULA, that was a custom chip made by Ferranti not available anymore. But the good news is that it has been manufactured (at least) three times with public schematics:

- Superfo Harlequin: A board 100% compatible (hardware, software and form wise) with the original ZX Spectrum. On this page (sorry, spanish) you'll find schematics and board files to get your own boards made. The main differences with the original spectrum are that the ULA has been replaced with TTL chips, two 32K RAM chips instead of 16+ chips on original Spectrum and everything works at +5V (the DC-DC converter was known to fail and blow the lower RAM). Also, it has composite video output instead of RF and optional RGB video output. You can put this board into a standard ZX Spectrum or ZX Spectrum + case.
- Harlequin 128k (on the same page): A expansion board / mod for the original Harlequin boards. It only provides 128k memory, not the other (AY) features present on 128k Spectrums.
- ZX-Uno: This is a FPGA based board that was intended to be a ZX Spectrum clone... but may emulate other computers ("cores"). The most developed core is the ZX Spectrum one (emulating every Sinclair and Timex model), but there are MSX, Nintendo Entertainment System, Sega Master System and even a PC-XT core. The storage device is a SD card, and it has PS/2 connector for your keyboard and composite video output.

I've got a Harlequin on a ZX Spectrum + case, and worked with everything I've got. IMHO is the best clone, and being manufactured with old TTL chips means that everything (except the SMD optional RGB output) can be soldered without any special skills. The ZX-Uno is a interesting toy because can emulate many 8 bit computers... but it's not really a ZX Spectrum clone.

On the non-freely (without schematics) modern clones (russians manufactured lots of varying compatible clones on the 90's), you can get a ZX Next or a ZX Vega, but I wouldn't recommend it. After all, they're not real clones (like the Harlequin)... and the ZX-Uno is cheaper than both of them.

ULA, as the name suggests, is a PLD. There have been some attempts to RE it and I think some people did? And even if not, the logic can be re-constructed in modern PLD/FPGA based on it's behaviour. I mean pretty much all it does it steal CPU cycles to do video output. AFAIR the very early ZXs had RAM refresh circuit done on a bunch of 74 logic, only the later ones incorporated that too into the ULA. One could start with ZX81, same configuration but simpler system - and then build on that.

Anyway, the idea to just sit and "build a computer" seems ridiculous to me, because I know what's involved. However I wouldn't be what I am now if someone kept telling the kid-me "you can't do that". So while I won't help, I don't have that kind of free time, I wanted to tell the OP to not give up his dream. Just be prepared for 2 things: that you will fail a lot, and that this hobby - like any other - costs money. And one advice I can give is to start with a repair job or two of some 8-bit machines like C64 or Atari (or indeed a ZX). While repair can be a tedious task, the ability to figure out where the problem lies is a necessary skill to have - as you have to assume your first project will not work properly from the moment you power it on. Either due to design or construction errors.

Tměř před dvěma roky jsem tady psal o Harlequin 48k, ale čas utk a tak se už někdy před rokem objevila verze 128k. I nelenil jsem a zakoupil desku ISSUE 1. Jenže než jsem se k tomu dostal, prošla deska dalšmi pr revizemi, kde přibylo např. skutečn časovn 128K. ISSUE1 totiž mělo sice 128 kB RAM, ale časovn podle Speccy 48k se 14 MHz krystalem, takže jsem neodolal a zakoupil desku ISSUE 2B. Pravda, než jsem se k tomu konečně dostal, už je venku minimlně ISSUE 2D, ale do toho už fakt nejdu .

Harlequin 128K ISSUE 2B m proti Harlequin 48k časovn i kapacitu paměti jako ZX Spectrum 128K, obsahuje zvukov chip AY-3-8912 a navc m i Kempston joystick port, resp. header, na kter si muste přidat vlastn konektor pro joy. Prostě takov ZX Spectrum +2 s Kempston joyem. Celkem fajn konfigurace a ždn nedostupn ULA.

Desku chvli trvalo osadit, součstek je na n jako mku, takže jsem si zapjel. Po zapnut se ovšem dostavilo velk zklamn, resp. ani ťuk. Když jsem tak zlehka šmtral po desce, chvlemi cosi jako obraz naběhlo, ale hned se to zase ztratilo. Napět jsem měřil už předtm. Bez napjen v pořdku bych do desky ani nenastrkal švby. Tak jsem holt musel na osciloskop. Začal jsem měřit od začtku, tedy od hodin a hned to bylo jasn. Hodiny nekmitaly a když jsem je šmtrnm tak nějak trochu rozkmital, tak kmitaly někde okolo 33 MHz msto sprvnch 28.375 MHz. Nejdřv jsem zkusil vyměnit 74HC04 v osciltoru za 74HCU04, jak doporučuje partlist k ISSUE 2D, ale to nepomohlo. Tak jsem se rozhodl vyměnit krystal a to byl sprvn krok. Po vměně krystalu hned naskočil obraz. Zajmav je, že osciltor chod s původnm 74HC04, zatmco se 74HCU04 ani nekmitne. Holt dělat osciltor s krystalem a dvěma invertory na thle frekvenci už je trochu alchymie.

Mm tu zmiňovanou desku Harlequin 128K ISSUE1, což je v podstatě 48k rozšřen na 128k paměti nebo by se taky dalo řct, že je to 128k s časovnm 48k. Lze to samozřejmě upravit dobastlenm pr součstek na časovn 128k. Deska mně na SellMyRetro stla 645 Kč, za 500 Kč bych Ti ji nechal.

Deska je deska, součstky na ni vyjdou tak na cca 2500,- osazen několik hodin, oživen dalš jednu, dobastlen pr součstek hodinu-dvě, vyzkoušen a mme cenu od pasu 5000,- Tak jen ať jsme v obraze ?