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First PCBs and testing

A project log for ZTO-80 Computer System

A powerful Z80 computer built around a highly expandable central bus design

jacob-hahnJacob Hahn 08/27/2019 at 04:562 Comments

A few days ago, I received an order of Z80 SBC PCBs for prototyping. I’ve been spending the past few days finding components and soldering, but I finished a board today.

One of the PCBs I had made

Unfortunately, I made the mistake of not soldering the large ground terminals of the serial port, thinking I wouldn’t stress the port enough to cause damage. Of course, once I plugged in a serial cable, the port flexed slightly, ripping the pad of pin 5 (ground) of the port off of the board. When I plugged the board in to test the output of BASIC, I got a few recognizable words but with lots of gibberish mixed in. I went ahead a used a enameled wire to connect pin 5 to a different ground pad, but the result was the same, so something else must have happened during the process of soldering or from the port damage.

A PCB with everything soldered and a few ICs

I checked the board thoroughly for any damage, such as broken traces, but could only find some scraped solder mask here and there on the back. Nothing major, and certainly nothing that would affect operation.

Luckily, I already have some new components ordered and I should be able to have a new board made by this weekend.

I’m also working on updating the PCB layout a bit for v2.1, including moving the ROM to the right a bit (so that I can use my IC prying tool with it!), a larger ground trace on the transistor array, and extended PIO pins. Thanks for the ideas, @Ken Yap!

Stay tuned, as I’ll be adding details and info throughout the week.

SBC V2 alongside SBC V1.1, my current working version

Discussions

Ken Yap wrote 08/27/2019 at 06:44 point

Could it be that the through hole for pin 5 is effectively a via that goes to other parts, say the MAX202, and the stress has broken the via, so you have to make more wire bridges?

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Jacob Hahn wrote 08/27/2019 at 12:29 point

Unfortunately, that’s not the case. The through hole connects directly to a ground plane. The issue could really be about anything, from bad connections and traces and contacts to damaged ICs, and my multimeter is in storage after having just moved, so I can’t test easily. I’m almost completely sure it’s not my schematic or board layout though. I’ll be able to get my meter within a few days and look around before building a new board hopefully, and maybe I’ll find the issue.

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