This page and the next pages you can visit from here document the information necessary to build the ZX81 Video Board V4 which can pair up with the ZX81 CPU Board V2 to make a working Euro-ZX81 assembly. Click the links above or below to proceed to the schematic, component placement diagram and partslist pages.

Some Notes

This is the Video Board V4, so it's the fifth version. (starting from V0) It was necessary to revise this board several times before I could get the final bugs in the display out. As stated on the main ZX81 page, there is still a little problem with FAST mode where the character lines are somewhat rotated in order(delay problem), so the display appears a little funny in this mode, though it is still readable. 
If you have a system configuration that operates constantly in FAST mode, for example a system which contains the ZX-Team LCD Interface where the ZX81 itself can operate in FAST mode while on the LCD the display is still in SLOW mode, then you can remove C23 so the display will be back to normal in FAST mode. Of course, when you go to SLOW mode without C23, the display will be slightly off similar to FAST mode with C23. SO only remove C23 if you're sure you will only be working in FAST mode.
As I stated on the CPU Board page, my strategy has been to have as much HC/HCT ICs as possible but unfortunately not all original LS ICs could be replaced by HC/HCT, so make sure you follow the partslist accurately since I can't guarantee good results in IC type combinations that differ from my partslist. Of course, you can always try your own combinations if you have other ICs than in my partslist, but be warned that you can run into problems. So the safest way to get the Euro-ZX81 up and running is to follow my partslists that are taken directly from my working prototype here. For more details why some ICs need to be LS types, read the Euro-ZX81 and Euro-ZX81 CPU Board pages.

You can see in the pictures(link below or on Pictures page) that I used pieces of precision IC socket as connectors on the board. They have many advantages, of which I find their relative small size and 0.8mm hole suitability most important. If I would use connectors that needed 1.0 or 1.25mm holes, the pads would have been much larger, so I would have had less space on the board. My single sided design technique is difficult enough as it is, so I always try to save space when I can. Also, these connectors have proven to be very reliable during my past years of prototype building.

Testing Info
There is a variable resistor on the Video Board, P1, which controls the video output intensity level. You can drill a hole underneath P1 so you will be able to adjust it while the boards are connected into an assembly. So if you can't make out a picture on your tv, try adjusting P1 and turn up the intensity and contrast on your tv, until you can make out a picture on the tv. Then you can put the tv back to normal settings and try to get the picture to appear properly by adjusting P1 again. Also note that it's a good idea to put both screen jumpers JMP1 and JMP2 on the CPU Board in position 1-2 to make sure you will have a white screen with black border which ensures that the 'back porch' of the video signal is a proper black level signal which in turn ensures proper contrast on the tv when you use its composite input. Later you can experiment all you want with several possible settings to see what you like and what works properly with your tv. If you use white screen and border, you may be able to improve the 'back porch' signal problem(which causes a very dark picture with the composite input) by using a tv modulator and the antenna input of the tv.
 

Pictures of the finished Video Board V3(!)

These pictures are of the Euro ZX81 Video Board V3, since I haven't built V4 yet. I have tested the changes that are present in V4 by wiring them to my existing V3 board. I will build V4 when I have the time. Note that the changes are implemented with CAD accuracy, so no risk to build this V4 Board while I haven't done it myself yet. The major I/O control circuitry in V4 is identical to V3. The changes in V4 were only done to improve the display quality.
 
 

Euro-ZX81 Video Board V3 Component Side	Euro-ZX81 Video Board V3 Solder Side

Some Further Euro-ZX81 Reading
To read more general info about the technical details of the Euro-ZX81 as a whole, go to the Euro-ZX81 Page.(See Navigation on the left)
It's also a good idea to read the faq document since it provides some additional info and tips.
 
 
 

With questions I can be contacted by email
 
 
 
 

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