Jupiter ACE (again)

General Chit Chat about Sinclair Computers and their Clones
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anightin
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Re: Jupiter ACE (again)

Post by anightin »

1024MAK wrote: Sun Aug 09, 2020 11:09 am Hi Andy

You say that it seems to be coming out of reset okay, have you tested any of the Z80s signals (e.g. /MREQ etc...)?

And have you done a visual check, it’s very easy to miss a solder joint on these boards because of the large number of joints required.

The transistor used for the master clock oscillator and for the clock signal to the Z80 have to operate at just the right point in their linear region. Otherwise either the oscillator will not oscillate (or will not be stable) or the transistor for the Z80 clock will not turn off fast enough (due to stored charge in it’s base junction). The result being the clock signal on pin 6 of the Z80 being continuously low.

Mark
Thanks Mark,

Yes the master clock is outputting a stable 6.5Mhz and I traced this through to the output of pin3 of Z9A (cnt0). This was then going into the 2369 transistor, but I had fitted an PH2369 and this resulting in a weak sawtooth output. I replaced it with a PN2369 and this looked much better. Pin6 of the Z80 is getting the resultant 3.25Mhz (actually reading 3.33 on my scope). I haven't looked at /MREQ but I watched reset transition okay and observed the address and data lines seemed to be toggling. In fact I accidentally shorted a couple of the high address pins by accident when probing and the screen filled with A characters.

The composite video transistor issue was that I was using was a BC548AC but the output seemed to weak. Replacing it with a 2N3904 seemed to give a much stronger signal.

Next job as you say is to check for dry joints. My guess is that there is something iffy with the part of the circuit that deals with video memory reads and writes, my hunch on this is when typing on the keyboard I do seem to get random characters appear through the 'snow', and mashing the keys and pressing return does affect the random patterns being output on the screen.
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anightin
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Re: Jupiter ACE (again)

Post by anightin »

Ace is now working!

There were 4 simple faults and one was down to me. I had missed soldering pin 14 of one of the video RAM chips -- good suggestion Mark. The one that deals with the high 4 bits. The other issues were PCB layout errors in that 3 keys had extra traces present that would have caused some confusion too no doubt.

Looks like someone else had already spotted the keyboard matrix issue so we must have the same repro boards :) https://youtu.be/PDVVFrXwiAQ
IMG_7547.jpeg
Screenshot 2020-08-09 at 17.44.44.png
IMG_7548.jpeg
... now on to build a proper keyboard :lol:

Btw does anyone know if fitting the pull-up resistors causes any issue with the standard configuration -- I suspect I'll need to fit them for my external keyboard
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1024MAK
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Re: Jupiter ACE (again)

Post by 1024MAK »

Well done :D 8-)

It depends on the values used!

I suggest that if you are going to use an external keyboard, then you may experience problems if you don’t fit pull-up resistors.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

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anightin
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Re: Jupiter ACE (again)

Post by anightin »

Right, that's the keyboard drawn up in Kicad. Now to do a quick check before sending off.
Screenshot 2020-08-11 at 16.18.31.png
Screenshot 2020-08-11 at 16.15.15.png

I went for Cherry MX1A 1U PCB Switches in the end.

I guess I'll go for blank keycaps with labels for a starter.


Update: Said labels attached
JupiterAceKeys.pdf
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Last edited by anightin on Sat Aug 15, 2020 7:03 pm, edited 2 times in total.
McKlaud
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Re: Jupiter ACE (again)

Post by McKlaud »

Congratulations.

From photos I can see this is not the board which I recreated. It seems to be a Russian PCB.

Good work with keyboard, and keep my fingers crossed for it.
Claudius
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anightin
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Re: Jupiter ACE (again)

Post by anightin »

Hi Claudius,

Thanks, Yup I can confirm it was a Russian seller for the main PCB.

I’m looking forward to getting a full keyboard working and the machine housed a case before I decide if I want to build any expansion boards.

I will have a few keyboard PCBs spare due to minimum order but let’s see if it works first :)


Also ...

I did see a video on mass storage using an extended ROM and a CF to IDE adapter, that looks interesting. Does anyone know if this was published at all online?
McKlaud
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Re: Jupiter ACE (again)

Post by McKlaud »

HI Andy,

You can find some information about the CF card mass storage there: http://www.jupiter-ace.co.uk/hardware_ACF.html

I am not sure if the modified ROM has been ever published.
Claudius
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anightin
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Re: Jupiter ACE (again)

Post by anightin »

Prototype Keyboard is working 8-)

Just a couple of niggles to sort out then I can share with those who want one:

1. A8 and A10 are swapped on my layout
2. The Symbol Shift is next to the Shift key instead of next to the SPACE key

Other than that, it worked first time :lol:
IMG_7600.jpeg
IMG_7599.jpeg
The D0..D4, Buffer Chip Select, +5v and GND are plugged in under the ACE using 90 degree single header pins so the keyboard can be unplugged without the need for de-soldering.

I'll send off for V2 at some point then I can fit my Cherry MX Keys and place it in it's case :D
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anightin
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Re: Jupiter ACE (again)

Post by anightin »

Now I've tweaked the board design to remove the previous issues, the new board works a treat!
IMG_7631.jpeg
IMG_7632.jpeg
IMG_7635.jpeg
IMG_7636.jpeg

Just offering the keyboard up into the donor case, hopefully it will fit with a bit of a jiggle...
7638.jpeg
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1024MAK
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Re: Jupiter ACE (again)

Post by 1024MAK »

Looks good 8-) :D

<Slinks away to go and shake the piggy bank to see what level the funds are at...>

So if you do sell some boards, I would definitely be interested in buying one ;)

The existing keyboard on mine is okay for occasional use, but does my head in if I actually try to code using it :twisted:

Oh, and do tell use about which keycaps you went for...

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
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