Amiga 600 schematics nearly put into Kicad

[demon-knight]

That board looks excellent, I bet the keyboard socket was a pain to solder?
Ah Settlers still one of my favorite games, played every version but never did finish the original, had one of the best intro's too.

[Jope]

Originally Posted by demon-knight

That board looks excellent, I bet the keyboard socket was a pain to solder?

There's no problem with that, it's a through hole part.

[Mick]

So do any electrical/math geniuses know how you can get a 180ns delay with an lumped element delay line?

[Eriond]

Wow, what excellent work! And so timely too, now that leaking caps has totally fubar:ed my A600. May I ask how much that last board cost, and which mfg. did you use?
Btw: Maybe it's time to remove that "nearly" part from the title of this thread?

[Mick]

It wasn't cheap and I also already had many of the parts, not half as expensive as buying all of the soldering/desoldering tools and other bits though. I saw it as more of an investment in self improvement though and not being able to solder in the Amiga community you miss out on a lot of good things, I wasn't expecting to succeed just thought what the hell if I'm ever going to practice now is probably the time. I think a temperature controlled iron makes a huge difference.

I'd like to know what value those capacitors are on an actual rev 2D board to finish schematics.

Gerbers I used are in zone.

[Eriond]

Sorry, wish I could help you there. Just checked all three A600's I had at home, and they are all 1.5 boards. I have one more, but it's on a long-term load to a friend, so I won't be able to check it for a while.
I have all the necessary equipment to both de-solder and re-solder all components, plus a healthy stock of the rare and unobtainum ones in case anything should go wrong Although I might just take the same route you did, and make my own board. Thanks anyways.

[Stedy]

@Mick,

Still no luck with my board. One more trick to try to see if the processor will boot, then I'll check all connections from CPU to ROM in case I damaged something by having the ROM incorrectly installed.

What do you need the 180ns delay for?

The resistor/capacitor values you're concerned about are the AC termination for clockes etc, their value will be tuned to each PCB, based on testing in the lab. Your design, with a 4 layer board and the typical spacing, should work well without as you have 60 ohm impedances.

If you have the Kicad files you used, I'll upload them to Github, https://github.com/istedman/A600Reborn

[AJCopland]

Congratulations on getting the board working Mick!

[Mick]

I was looking into bandpass filters and delay lines, the circuit seems easy enough but there is a lot of math involved with passive delay lines.

I'd like to just see what a real board used for those parts and also I noticed 2D has a ferrite bead at E199 instead of 27 ohm resistor, what value? the values I've used work but I'd like to get it right using an actual board, even if boards varied.

[seb132]

Mick, my apologies I couldn't go through all the thread (I will, though, because it very interesting as I have more than 10x A600 myself...), but could you please tell me what is now in the location of the RF modulator?



Thank you!

Superb work, by the way, I'll definitely build some when the project will be completed...

[seb132]

Originally Posted by kipper2k

I have also completed and tested a straight forward complete keyboard and plate replacement that will use cherry MX keycaps and connect to the regular A600 motherboard connector. I will show it off probably next week. Keycaps will be the original Amiga keycaps. More info on that later.

Wow, did that ever show up ?
I missed it if so...

[Mick]

Originally Posted by seb132

Mick, my apologies I couldn't go through all the thread (I will, though, because it very interesting as I have more than 10x A600 myself...), but could you please tell me what is now in the location of the RF modulator?

It's an S-Video connector, TE Connectivity 5749181-1. I added the old RF mounting holes in case people don't want it but would rather install a mod designed to use the original modulator mounting holes.

It's done apart from a few questions surrounding some capacitors and ferrite beads used by Commodore in retail boards. 2B and 2D boards are not that different just different footprint sizes for SOIC so I'm assuming changing E199 from 27ohm resistor to a ferrite bead in the time between 2B and 2D was done more for performance reasons. What value is it though?

[Stedy]

Hi,

I made some more progress with the board this weekend, it now reads from the Kickstart ROM! I ended u doing a continuity check of every pin of the CPU to a point somewhere on the PCB. When I got to literally the last pin, DTACK, I found an open circuit on /DTACK. Tracing the circuit, I found R113 was tomb-stoned near GAYLE. A quick resolder job and when powered up, I saw activity on /DTACK, RnW and the other control bus signals! I plugged in DiagROM, hoping for something on the serial port, nothing.

The serial port CIA had no data bus traffic, tracing back I saw that the CPU/custom chip bus buffers U21/U22 were not working. Have not found out why yet, I ran out of time. I have some logic analyser captures and oscilloscope captures, I'll put them on the Github Wiki soon.

[Pyromania]

Will anyone be selling boards that can be populated with A600 custom chips?

[SukkoPera]

I have a 2D board. E199 is a 27 ohm resistor. What other values do you need?

My 2 cents: make the video section 1:1, just add a proper resistor footprint for the 2.61k resistor for this mod, as that's what I would be using, there's no point in going crazy chasing custom components that are nowhere to be found.

If you want to do a few other useful minor tweaks, here's my 2 cents:
- Make all the pads for the through-hole caps much larger, and use thermals for those connected to ground.
- Use thermals everywhere.
- Increase the spacing between the RAM chips and maybe move the caps to the shorter side to make them easier to hand-solder.
- Move the caps between the keyboard connector and the audio connectors somewhere else. Or move the keyboard connector.

If you want to go for something more challenging:
- Add space for 2 more RAM chips.
- Add (optional) RTC circuit.

Anyway, great job so far!

[Mick]

If I did 1:1 it'd need testing and for that I'd need replacements for the BPF and DL, I would have preferred to do 1:1 in the first place but without those parts it can't really be tested. BPF looks easy to do but I can't work out the math necessary for a 180ns delay using an LC circuit.

I'm pretty much sick of the sight of it now, if people want to change anything they can learn Kicad it's worth it and can only help the community going forward. If I can solder it I'm sure others can with the right tools.

The only values I need checking now are these capacitors:

Originally Posted by Mick

C7, C8, C9, C29, C28A, C28B, C36.

You might only need to measure one or two of them they should all be the same.

[Mick]

Oh yeah and check to see if C26 is connected to VCC, I was looking closely at a 2D board and it appears not to be.

[Stedy]

Hi,

Mick, I'll check those capacitors in the next day or two and confirm the results. I could design a delay line for the video circuit quite easily, for the bandpass filter, I need to know how wide the pass band is. Could not find a datasheet for the Sony recommended part.

Newer video encoders do a much better job of making composite video, hopefully the CXA2075, which does not need the delay line or bandpass filter gives higher quality video. The composite video on the Amiga is quite bad.

The original 1:1 copy design is on Github, when Mick has the final few queries answered and released the KiCAD files, I'll upload the version with S-Video. From there, anyone can take the design, create a fork and customise the PCB to their needs and sell PCBs if they wish.

[Lemaru]

Originally Posted by Stedy

The original 1:1 copy design is on Github, when Mick has the final few queries answered and released the KiCAD files, I'll upload the version with S-Video. From there, anyone can take the design, create a fork and customise the PCB to their needs and sell PCBs if they wish.

I have a few ideas for some mods for my personal use. Never had a PCB of this size made, what's the pricing like from somewhere like JLCPCB

[seb132]

In Europe 5x A1200 boards (green) cost 90€ shipped... so I’d say a bit less for A600?

** Edit: What mods would you do?