Buiding up and testing the ZX81+38 revision 1,9

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Revision as of 16:35, 7 May 2023 by Mahjongg (talk | contribs)
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Project Building up the ZX81+38
Diodes op zx81+38.JPG
A manual on how to build the ZX81+38
Status Initializing
Contact mahjongg
Last Update 2023-05-07

For those planning to build the ZX81+38, note this kit is NOT suitable for people who are not proficient in soldering. The ZX81+38 is not easy to solder, the design is dense and the solder pads are smaller than in most other designs. Also you will need to have the right tools, and probably a loupe or soldering microscope. You also need to own an EPROM programmer. I suggest using the minipro TL866CS to program a 27C256 with four copies of the ZX-81.ROM file.

Make sure you use the latest files for the PCB, BOM and component overview drawing, and schematic, at this moment these are revision 1.9.

Start by soldering the lowest parts, that is , te flat lying resistors, and the resistor packs, and the diodes (the nine 1N4148 and the single skottky diode), also the three main sockets. see this picture:

Low components first.jpg


Then add the IC's be careful to place them in the right orientation, and the right spot referencing the component buildup drawing:


Note that I'm not using sockets for the other IC's, but you can if you want, if to use dual wipe sockets, NOT round machined sockets, they are a disaster to put IC's into, and are not as reliable as they seem to be.

Then use the latest version of revision 1.9 of the component overview drawing, that is the drawing where the 15pF capacitors are BELOW the crystal. If you could not find an SMT type of this crystal, the one that comes with a plastic carrier and flat pins sticking out besides the metal can, then convert your pin though hole crystal to a SMT solderable one by sticking the pin wires through a piece of paper, fold the pins flat sideways, and cut the wires off just outside the paper isolation.then solder the pins to the solder pads beneath. If you are carefull not to cause a short between the pins and metal can you might leave out the paper isolation, see:

Kristal legs bent.JPG

Now you can start with the small ceramic capacitors, use the component overview drawing and a highlighter marking which capacitor you have done. Start with all the special capacitors (all non 100nF decoupling caps) like the 15pF caps, and all the others, then add the 100nF decoupling caps. as in this picture:

File:Then all ceramic caps.JPG