Assembly, Test and ... Aaargh !

 

After half a day of soldering, the board looks like this:

Everything fits like a charm, and it really starts to look like a Jupiter ACE. So it's time to start testing, and carefully insert all chips.

Step 1: Check what is + and - on the power connector. It turns out the Tip is ground, and the sleeve is +. Found myself a leftover power supply (12VDC/1.4A)  and mounted the 3.5 mm jack plug. Once connected the LED goes green ! This is always a good start. After that I measured the supply voltage on all main chips like the Z80 and some of the 74 series. All seems well.

So I first mount U23 74HC86, which is part of the oscillator, so now we should the 6.5 MHz on pin 8.

Which does not happen. There is a clear oscillator signal (with the right frequency) on pin 9, but its simply not big enough:

The signal gets bigger if I replace R2 with  a 470K, just enough to get the signal on pin 8 going:

 

Still looks a bit wacky, but I think that's also a limitation of my oscilloscope which has a maximum sampling rate of 25 MHz so there are only 4 samples per cycle.

Inserting U9: This is the clock signal divider, so there should be a clock on pin3 of U9:

 

Well, at least it starts looking like a square wave now. So lets insert the next two counters, U10 and U11. Which seems to work as well, so lets mount all other chips. All good, until I came to inserting the RAM chips:

OH NO !! The footprint is wrong. It took me about half a second to realize what was wrong: I selected the DIP28 footprint for this DIP24 chip. Not something KiCad will warn you for, after all the DIP28 has plenty of pins for a DIP24. After about  10 minute of quiet contemplation (...) I decided that I would have to make some kind of adapter with 28 pins on one side and a 24 pin socket on the other so I could re-route all pins from 12 and up.

Good plan, but after struggling with the first four wires, and realizing I would have to do 3 adapters in total I gave up. Opened KiCad again and designed an adapter PCB in about 30 minutes. Checked with the PCB manufacturer and found that it would cost €19,- to have 15 pcs manufactured.

So we'll have to wait another week until these boards arrive and the testing can continue.

Creating the PCB

After drawing the schematic and switching to the PCB design, the first thing I did was to arrange all components in a similar way as on the original board. Since I did follow the slightly modified version of the schematic with different memory chips, I had to make some changes, but overall the look is similar.

Original board layout, by Grant Searle

 

 

 

 

 

 

 

 

Layout, and ratsnest lines

 

 

And so, after more than a year, (where I decided multiple times that it was just to hard and almost gave up), it is finally completely routed:

And since KiCad has a 3D display tool, I can now compare my version to the original: