ZX Spectrum do it yourself

"For 8 years I played in the Spectrum in black and white and everyone knows why, but because our valiant RGB TVs did not understand the signal at all." I would like to say, for good reason, remember that the sun used to be brighter and the grass is greener. But I will not say, in my childhood the word Spectrum in general, no one ever uttered. All my childhood I played dandy, later in sego, sometimes with friends in the supernintendo. Neither in the Dandy program “New Reality”, nor in “From the screw”, nor in any magazine, have I heard about this computer. I had heard about computers booting from cassettes, but I never saw them and did not know their names. For the first time I found out about him only when I got the Internet. I read the forums, I envied those people who collected their computers themselves in the late 80s and early 90s, but I missed my year. Although in those years I was small and with all the desire I would not have collected my clone of the Spectrum. Have I lost much? This is the question I started asking myself not so long ago. A year ago, I came across a very good vidosik where one guy spoke in great detail and showed how to solder a clone of the Spectrum “Leningrad”. I reviewed it more than once and finally decided “I will assemble my computer from scratch!”.

I decided to take the original scheme of Leningrad with sblive.narod.ru as a basis. Well, add a bunch of improvements, such as adjusting the drawing of a circle (it is not clear how Zonov could design a computer with such a cruel jamb. It is expressed in font problems, jambs of graphics, etc.), stabilizing the crystal oscillator, stabilizing the frame and line synchronization, modifying the INT signal, introducing reference to black level.



To make this process even cooler and more interesting, I did not begin to search for a ready-made board, I ordered myself a quite compact 12 * 18 breadboard. I also had to order microchips and other small items from aliexpress and Chipip. Memory and processor had to drop out of the broken clone, which I recently received from one spektrumista. I still don’t know what kind of clone it is, there is no circuit for it, and I just dropped it from it.



I decided to put all the chips on the panels for quick replacement if something goes wrong. But after all the Spectrum contains a ROM, and it still needs to be flashed, I did not have a programmer, but the world is not without good people. Instead of two EPROMs, I decided to put one EEPROM W27C512, in which I sewed 48k BASIC, 128K BASIC, TR-DOS and memory test for 48K, it is also a good idea to be able to switch memory banks with jumpers. But here all my details came, having thought over in advance where which socket would stand, began to solder them. Well, I stuck stickers on the board with inscriptions where there is a chip and leg numbers, which made life easier for me in the future.





Giving a couple of hours a day for two and a half weeks, I still collected. I could not wait to connect it immediately. And after switching on, I saw a white screen, which I thought was pretty good. After rechecking the entire board, removing the pair of jambs did not make things any better. I could not understand what was happening for a long time, but then I learned that you should not interfere with CMOS and TTL microcircuits. Yes, I'm still a radio amateur. I had to order parts again and wait. After replacing all the CMOS chips on the TTL, the cherished inscription still appeared, but the image floated.



Contacting the zx-pk.ru forum made it clear in part what was happening, but I did not have a solution. As a result, we had to sit for hours on the scheme. And voila, I just misunderstood the INT signal generation refinement scheme, or rather, I first understood it correctly, and then I thought that I did the wrong thing with the joint. Well, another problem has been fixed. But not everything is as rosy as we would like, on my multimedia monitor the frames were constantly running. And then I decided to connect with the good old TV SHARP, which never let me down. But the truth is in h \ b, since there is no RGB scart in it. And the picture on it almost did not twitch. Again, addressing the forum gave good advice, to make a filter for a switching power supply.

And finally, the picture is normal, no twitching, we run a memory test.



But for the Spectrum also need a keyboard. Then I got out pretty original, took the old keyboard, pulled out a film with contacts from it, cut the Getinax into pieces, soldered the contacts to it, processed them with a file and glued it to the keyboard with hot melt, and soldered them according to the scheme. The result was a rather cumbersome external clave. Well, the ports for the Sinclair joysticks are built right into the keyboard. Joysticks from sega master systems or atari are suitable, well, or, as in my case, a segovsky joystick that was soldered inside, for which I brought up the spacebar (namely, it is almost always used as an additional one) to button A, and when you press button C, pressing up is duplicated which is convenient in platformers.





With the speaker, it wasn’t like me and I just brought the beeper to the TV, so at least the volume can be adjusted. Having written a simple melody in BASIC, having tested the sound, I decided to download some kind of game. And ... I did not succeed. He collected the tape reader on the K554SA3, tried several chips, rechecked the entire circuit, but it didn’t start, so it’s still not clear. I reassembled the reader on 561ЛН2 according to the scheme from the Pentagon-48 (first on the breadboard before soldering) and it all worked the first time. Although the games were loaded, most of them hung up right away, some of them, like DIZZY 5, managed to play a little.



Once, when I woke up in the morning, I wondered if I had the correct capacitors soldered ... and OMG, instead of 47 nanofarads, I soldered 47 picofarads, and also wanted something to work. Once again we order the missing parts, waiting. After the global soldering of capacitors, you can finally play around normally, nothing else hangs. I had to reassure myself that all the same, most of the games on the Spectrum are monochrome and I don’t lose so much that in the late 80s not all people had color TV sets and many played it with a B / W picture. But somehow it didn't help much, you know.



And on my LCD monitor, the frames still ran. In the end, I still decided to solder an additional microcircuit to shorten the horizontal sync pulse, which I wanted to put at the beginning of the assembly, but for some reason I decided to save. In the end, finally got a good color picture.



The image is really a bit double. Checked on the LCD TV, doubling is not visible. The picture is great. Super! But there is still free space on my board and it would be foolish not to use it. It would be great to make an expansion of memory up to 128k and play in 2015. To do this, we will change our K565RU5 to K565RU7 or analogue MN41256-08, which you can easily buy for aliexpress. Having added 7 more microcircuits, including the sound chip YM2149F, the board filled in completely. There were no problems with memory upgrade. Expanded memory to 256k according to this scheme, but I still use it in 128k mode.



The result was this.







Initially, I did not intend to use the board on the table, and for this I picked up the case from the old set-top box, theoretically, you can also install an extra controller board fee on the second floor, but I don’t want to bother with it yet.







The specs turned out to be fierce hardcore, I managed to get through only the recently released Mighty Final Fight.



How much have I lost due to the lack of this computer in my childhood? In terms of games, it is unlikely, although the possibility of rewriting games from tape to tape would be very pleasing to me. In terms of programming in BASIC, it would hardly have interested me at that time.