This was a very exciting project for me to work on. The Sinclair ZX Spectrum computer has always been really interesting to me(our first family computer was a Timex Sinclair 1000!), but being in the USA, I wasn't sure I'd ever have a chance to own one. Natively, it is a British PAL machine, so the whole PAL/NTSC issue was really discouraging. After all my research over the years, I had pretty much given up on the possibility of having my own NTSC Speccy. There is an LGR video on YouTube, where the guy sets up a ZX Spectrum in America. He had to mod the RF Modulator to output Composite video(not a big deal), used a TV with PAL compatibility, used a voltage converter, etc, etc. There's also a video here, which shows a similar set up. It's awesome these guys have Spectrum's running in NTSC land, but that is way too much for me personally.
My interest never died though and one evening I was looking for Spectrum's on eBay. Lo and Behold! The Superfo Harlequin ZX Spectrum clone PCB!
"A couple of years ago, Chris Smith reverse engineered the ZX Spectrum
ULA (you can obtain the ZX Spectrum ULA Book to read about that).
Chris also developed the Harlequin: a ZX Spectrum 48K clone based on parts that replace the ULA, so no ULA is needed.
ZX Spectrum fans continued on this development which resulted in the
design that is now known as the ‘Harlequin Superfo’. The current rev G
is the most stable one.
You can now assemble a complete and 100% compatible ZX Spectrum 48K clone yourself!" - ByteDelight
What really piqued my interest with this, was that it claimed to have NTSC support as an option and that it was a 100% compatible 48K ZX Spectrum clone. I read everything I could find online about the Harlequin, but it was mostly in other languages. I did manage to find a guy named Sergey living in the USA that built one and he was helpful in answering some questions for me. He posted a lot of info over on his blog here, which I highly suggest checking out. He even has a Bill of Materials on Mouser that he put together. Very cool, thank you Sergey!
Continuing... There are a few people out there selling different Rev G PCB's. Some are Red, Blue or Green, some have ENIG finish, some come as complete DIY sets with all the parts, etc. I ended up deciding to make my purchase with www.ByteDelight.com, because Ben Versteeg sells everything you need for a complete setup. For around $200 USD including shipping, I was able to get a Harlequin Rev G kit with all parts(includes presoldered SMD parts), an original 48K ZX Spectrum ROM and an original rubber keyed case with a new membrane.
For me, I really wanted this to feel authentic and when I added up all the parts(if I was to order from Mouser), it really wasn't going to save me all that much money ordering all the components separately. Also, Ben is a very nice guy and even tested NTSC output and added some corresponding information in the included manual before my order was placed. Oh, and he also made sure I got a 3.579MHz crystal, which is also needed for NTSC. Thanks again Ben!
I got my package from ByteDelight after about 2-3 weeks(they are located in Holland). Ben packaged every component in separate baggies and marked them, which made following his manual about as easy as a project like this can get. I was also given a tracking code, which was nice.
The amount of soldering on this project is pretty heavy and was slightly daunting at first. I did the Diodes and Resistors first and split the project into two soldering sessions. All together it took me about 5 hours total I think. I really took my time, making sure everything was done correctly. My only error during the building process was soldering on the C3 - 680μF capacitor normally, instead of turning it on its side(laying flat). If you don't do that with a cap higher than 8mm, you can't close the keyboard/case. It was easy to correct.
After soldering on all the IC Sockets, Transistors and Capacitors, it was time to install the Pin Headers(jumpers), the two crystals, the connectors for the DC Jack, keyboard, Mic/Ear, Composite Out, RGB and also all the IC's.
One of my questions was not knowing exactly what type of power supply to use for the DC jack. I was told that any AC 7V - 19V or DC 9V - 27V, 5.5mm plug with 2.1mm pin should work. An original ZX Spectrum power supply can be used (but that is made for 50Hz I think). Which also brought up the question of polarity of the plug/pin of the power supply. Most of the modern AC adapters I found had positive center pins, whereas the original ZX Spectrum power adapters had negative center pins. I asked both Ben and Sergey about this and was informed that the bridge rectifier (D12) makes it possible to use AC and DC power supplies, no matter how the positive and negative voltage is connected.
My chosen power supply:
Input: 100-240VAC 0.3A, 50/60Hz
Output: 9V 2000mA
Center Pin: Positive
Plug: 5.5mm, 2.1mm pin
That seemed to work fine for me. After putting everything together, I plugged the power in and was greeted with the lovely Sinclair Research Ltd. screen!
Next, I tested out some software. I had already purchased a game on cassette, so I plugged in a generic cassette recorder and did the old LOAD ""... Immediately the game began loading and everything just seemed to fire right up. I was warned that there might be some video weirdness running some of the Spectrum software and I did get some kind of odd dot crawling, rainbowey effects. Pretty odd.
I had this connected to a Commodore 1702 monitor through the front Composite jack. After connecting it to a Polaroid FLM-1511 LCD tv, the video output seemed to mellow out a bit. I'm not 100% happy with the NTSC composite output I'm getting so far, but not sure exactly what I should do about it yet. There is an S-Video mod discussed here, which Sergey said he did and had good luck with.
The Harlequin has an RCA Composite output and an RGB 8 pin mini-DIN output for video. The best option would be using the RGB mini-DIN, but being located in the USA, this only seems possible by modding(like the above link) or using some sort of SCART converter box.
I tried wiring up some inexpensive SCART/S-Video SCART/Component adapters following the RGB-to-SCART diagrams, but haven't had any luck yet.
I am having enough fun with this little computer, that I'm not too concerned about the video quality, but I could see some users being put off by the Composite video output. I will be sure to post more info on this subject down the road, if I start getting better results. If any NTSC users have done the S-Video mod or have come up with something cool to improve video output, I'd love to hear from you in the comments section.
This clone seems to be directed more towards the European PAL user, so just having the option for NTSC is fantastic to me. I am very happy the designers took these things into consideration.
Finally owning a working ZX Spectrum in the USA is somewhat of a dream come true for me. I am very fascinated by the bright colors and the crazy amount of games available.
For all of you NTSC builders, this might be helpful...
J9 - AD724JR PAL/NTSC encoder (1-2 NTSC)
J10 - Switches horizontal sync frequency (1-2 NTSC)
J11 - Switches vertical sync frequency (1-2 NTSC)
J12 - ROM configuration (2-3 for original ZX Spectrum ROM - could be different if using EPROM)
J13 - RESET (I left this open, since I don't have a reset switch installed)
J14 - Voltage Output (Not used)
J15 - Speaker (1-2 ON, 2-3 OFF)
J16 - Voltage Output (Not used)
Y2 - 3.579545 MHz for NTSC (this is important!)
To sum this post up, I would like to express my thanks to the following people:
Chris Smith - http://www.zxdesign.info/harlequin.shtml
Jose Leandro - http://trastero.speccy.org/cosas/JL/Harlequin/superfo1.html
Miguel Angel - http://www.zxprojects.com
Ingo Truppel - http://www.trupel-online.de
Ben Versteeg - http://www.ByteDelight.com
Sergey Kiselev - http://www.malinov.com/Home/sergey-s-blog
Don "Superfo" Dindang