Open Points

[SukkoPera]

Some things need to be taken in consideration before making the first PCB prototypes for this project, regarding components that might no longer be easily available or are much more expensive than other modern equivalents.

1. All the ceramic caps are of the axial type. These are hard to come by nowadays and way more expensive, so they can be replaced with radial types, which are way more common nowadays.

For instance:

• Kemet C410C103K1R5TA (10 nF) is 0,078€ at 300 pieces
• Kemet C412C334M5U5TA (330 nF) is 0,098€ at 200 pieces
• Kemet C315C103M5U5TA (10 nF radial) is 0,049€ at 500 pieces
• Kemet C315C103K1R5TA (10 nF radial, 100V +/-10%) is 0,049€ at 1000 pieces
• 330 nF radial are actually more expensive (!)

2. The various per-chip decoupling caps have different values (mostly 10 and 330 nF). Maybe 100 nF will be fine for all of them?

• Kemet C320C104K5R5TA is 0,054€ at 500 pieces.

3. C401 and 402 (video power) are specified as 1000 uF, but these had higher values in older revs, as I've personally seen up to 3300 uF. While 1000 uF can be fine, we might change and move their footprints a bit so that physically larger caps will fit (they always had a hard time anyway, even of older boards there wasn't enough room!). A quick search on RS shows that a diameter of 16 mm should be enough. Good candidates are Panasonic EEUFS1C332 (16V, 12.5 (Dia.) x 25mm) or EEUFS1E332L (25V, 12.5 (Dia.) x 35mm). The FS series has very low ESR. The original footprints have a diameter of 8 mm and a pitch of 5 mm.
=> Moved to #16

4. What about LF1? Can this still be found?

5. What about the various EMI filters? Some information here.

6. What about the power connector? This is definitely nowhere to be found. Maybe we can consider DIN-5 (can carry up to 4A@24V)? In that case we should come up with a footprint that can either fit a salvaged original connector or our replacement.
=> Moved to #17

7. Even worse, DB-23 connectors are basically extinct. What shall we do?

8. Even the 5x Resistor Arrays (isolated, not bussed) do not seem widely available. We need them in 39, 47 and 68 ohm values. They aren't crucial components (they're there for EMI, I think) and can be bridged, or maybe replaced with single resistors.

[ZaPpi3]

How about replacing the DB23 altogether with an RBG socket, so a cheap off the shelf RGB to SCART socket could be used?

[SukkoPera]

@ZaPpi3 What "RGB Socket" do you mean exactly? Keep in mind that the mainboard should still fit in the original shield and case.

[ZaPpi3]

There are many to choose from, I would personally use what the Spectrum Next uses as it's a standard VGA. The cables and connectors are cheap and plentiful. It also wouldn't be hard to have a second sound output routed next to the VGA connector with a 3.5mm stereo jack. This way you could use the Spectrum Next SCART lead that incorporates the sound and video.

This is the ideal cable for video only: https://cpc.farnell.com/pro-signal/psg00969/21-pin-scart-to-15-pin-hd-plug/dp/AV14656

[SukkoPera]

I've been thinking about this, but I'm not sure it's a good idea, as it would imply losing compatibility with genlocks and all the existing cables.

[shred]

I'm currently assembling a bill of materials for the Rämixx500, and trying to find as many components as possible.

Can you give me a hint about the ferrite beads E431-E435 and FB802? What did you use there?

[SukkoPera]

Hey @shred, nice job! Please have a look at #22 and post any questions there.

[shred]

Thank you! The list was a good help for the last two missing pieces. If you like to, feel free to link to my BoM. I'd also appreciate your feedback if something isn't correct.

[SukkoPera]

Will surely do, thanks for your contribution!