Originally posted to Patreon, October 2024.
The PCBs arrived a while ago, but now is time to assemble a Mini VIC.
I have not made many yellow PCBs before, but this just seemed an appropriate colour match.
I put together the parts required. This is a new kit, so may need further tweaking. Lots of similar resistor values, 220Ω, 240Ω, 470Ω, 510Ω, etc. can these be optimised?
I did consider packing multiple kits, but I think a one off will do for now. (2025 update - still tweaking things - almost there)
That all went together without a problem. The edge connector for the cartridge port went in easily. On the previous board, I had the holes too small, so it was quite a job to finagle all the pins into the socket at the same time.
I don't like the way the sockets look when there is a mix of 14 and 16 pin chips, but when the chips are installed, or they are soldered direct they all align nicely as the 14 and 16 pin IC bodies are the same sice. I definitely need sockets in this case, there are likely to be some bodge wires appearing (2025 update oh yes, so many wires....)
Actually, there was one problem - the power switch.
I had carefully searched the datasheets for the exact type to match the original (top).
The one bottom left is the closest match. The right hand one was more easily available, but the rocker is too big for the case.
However, it appears there is one difference I had missed. The footprint is the same, but the pins at the front that are for support only are different.
The current type have a sort of ledge, which causes the switch to sit a few mm off the board.
The originals just had a pin, so it sat flat, something like this.
I have looked around and it seems those are the only type available now. I should be able to get around this by changing those pads to slots to allow the switch to sit flat as required.
For the moment, I attacked the metalwork with the side cutters.
That fits much better.
You will also notice above the switch there are extra pads around the power connector.
This is to allow a 2.1mm DC jack to be used instead of the 7 pin DIN.
I know the VIC20CR / C64 7 pin DIN power supplies are known to be unreliable, but I am not actually connecting to the 5V which can fail, I am using only the 9V AC, which is just a transformer winding, so should be fine.
Actually, it will probably be better than a modern switch mode 9V or 12V supply, and is a good way to use a power supply you wouldn't normally touch with a barge pole, and also one that goes perfectly with the machine.
I think this is the first time I have put a fuse on one of my designs, just staying true to the original, I guess they thought it was necessary.
Time to install all the ICs.
Well almost all of them. All the ones fitted are modern, still in production, low power, high speed CMOS chips.
The VIC chip is the one part I do not have a suitable replacement for yet, but let's test everything else before committing to trying with a precious VIC chip.
5V power is good, reset is there. It's about 2 seconds, maybe a bit long, I might reduce that a but by changing the resistor value.
The clock is a bit rubbish though.
Not sure what is going on there. I had a few issues with the scope / probes here. Both clock signals look awful, but they are different shapes. The trouble is when I swapped pins or entire scope probes, the top trace still showed the spiky stair version, and the other was showing something more rounded?
They have both been adjusted on the probe compensation pin. Something to look at another day, hopefully it will be good enough.
Time to try it out.
(imagine a picture of a black screen here)
The video output is disappointing though, black screen. Sync but no signal.
So the VIC chip is running, but has not been initialised.
I had set this board up to work with either a W65C02S or a MOS 6502. I wasn't sure if that was the issue, so I fitted the jumper (to get around them not being quite pin compatible) and a 1983 6502.
And that made no difference.
(another black screen picture)
I tried various things with the clocks (more in the next post), but finally gave up for the day.
...... time passes ......
The next morning, I was planning to write some test ROMs to toggle bits on the userport and things like that. But first, I decided to check the board over to make sure I hadn't made any stupid mistakes, like the wrong chip, or a bent pin or ....
.... a missed solder joint.
That would do it.
Let's try again.
Yay! A ready prompt!
10 PRINT tested
OK. So far so good. The video output is not great, and there may be a glitch in the colour RAM, but let's skip over that for the moment.
When I started out with projects like this, I like to set a goal. For the Minstrel 3, this was being able to play 3D Monster Maze. For the Mini VIC, it was loading Cheese and Onion from the Penultimate and it playing properly with the wider screen etc.
Nice, the cartridge port works, as does Cheese and Onion, sound and the joystick.
Rude not to have a go at EMH whilst I am here, make sure it's horizon trick was working.
A bit more testing, and the Penultimate passed a self test,
The Mini VIC passed the dead test. I will need to dig out the Commodore Diag cartridge and test harness and give this a full test later on, but so far so good.
The video output is not perfect, bit of a blue line to the left of the white.
The board is setup for Composite and S Video output, so I will give that a go when I make up the appropriate leads. I suspect the video circuit needs a bit of tweaking with values etc. I think I based it more on the one from the C64C, I might have to reconsider that.
There have been a few glitches in the colour RAM. I think may be related to the clocks. (the first sign of the mods there)
I thought it could have just been a flaky VIC chip, so I fitted a ZIF socket and went through my spares, but they were all basically the same (the working ones at least).
I also tried an NTSC VIC chip to see if that was any different. The video was clearer, no blue line, but still the occasional glitch with the colour RAM.
The plan initially is to go for a VIC20 replacement board.
I would like to also do a version with built in keyboard, but I think I should wait to see what happens regarding alternatives to the VIC chip.
Let's see how it fits in a VIC20 case.
Nice.
All looks good on the side as well.
Looks rather splendid, doesn't it.
Adverts
The Mini VIC kits are not available yet, but there are still Minstrel 2 and Minstrel 3 kits available.
You can now get a Minstrel 2 kit for $200. 1980s pricing.
Or you can get a Minstrel 3 kit for $200
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