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nam9

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Great to see people are still improving this design @rsignal.
If you'd like to go for broke, do you think it would be possible to add the option to accept either CSync or H/VSync input to your model?
 

pacoarcade

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Diode package is SOD-123. Resistors and ceramic capacitors package is 0805. Be sure to solder the diode with the correct orientation according to the schematic.

Using a 2K pot instead of 1K for RV1 is maybe better. 1K is what I have on hand and it works for me.

This is just an early prototype, it needs some work. Each TTL chip should have a 100nf decoupling ceramic cap.
 
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pacoarcade

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Great to see people are still improving this design @rsignal.
If you'd like to go for broke, do you think it would be possible to add the option to accept either CSync or H/VSync input to your model?
I'm not sure what would be the best way to combine HSync+VSync into CSync, any suggestion? this would be useful for regenerating CSync too. Anyway you could do that with other circuit and plug the output into this circuit input.
 

nam9

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And here is an update to the schematic to include H+V sync combiner on the unused gates on IC2

Yes, yes, fix v1 before adding features. (Credit philmurr, UKVAC)

@rsignal
 

pacoarcade

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@nam9 Although I'd like to incorporate a H+V sync combiner my priority is improving the basics first.

I've ordered some pcbs of this new version, will share results once tested. Although I can share the gerbers with anyone interested (just send me a PM)

After doing some tests with 74AHCT1G17 Schmitt buffer with mixed results (works fine with all boards tested except MVS) I've incorporated a 74HC14 buffer as RGB explains followed by a voltage divider in a similar way used in Tim Worthington's AV-Driver, but using common 470R and 75R resistors instead of 475R and 82.5R. This way TTL / 350mV CSYNC is selectable by a jumper.

If this work I'll adjust R1 and R2 for 75ohm impedance matching taking into account the output impedance of the 74HC. I think it's 470R and 87R being 50R the output impedance of 74HC to get ~400mV, but I need to double check this.


The circuit also features a DPDT switch to enable or disable Martin Jones' CSYNC processing, making a total of 4 CSYNC modes.

Bugfix: Unused 74LS86 inputs are now connected to ground.

Update: The circuit is wrong since when "REGEN" is off there are floating TTL inputs. I use the same circuit as in this post but using a 74HC14 buffer.
 
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invzim

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Although I can share the gerbers with anyone interested (just send me a PM) I prefer to test before making them public.


After doing some tests with 74AHCT1G17 Schmitt buffer with mixed results (works fine with all boards tested except MVS) I've incorporated a 74HC14 buffer as RGB explains followed by a voltage divider in a similar way used in Tim Worthington's AV-Driver, but using common 470R and 75R resistors instead of 475R and 82.5R. This way TTL / 350mV CSYNC is selectable by a jumper.
Testing boards before releasing, and showing the schematics is the way to go, great job!

What issues did you experience with the schmitt and MVS?
 

pacoarcade

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With MVS I get no output signal from the 74AHCT1G17, so I'm looking for alternatives, like 74HC14 used by RGB or 74HC04 as suggested by mikejmoffitt in this thread.

I opened a thread with this specific problem here.
 

pacoarcade

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Thank you! I'm glad it's useful for you.

I used a Cadillacs and Dinosaurs copy and a Blaupunkt 14" CRT TV. Unfortunately I don't have a Taito F3 to test, but it should work since in previous posts people had success and the only change in the circuit is the 1K pot working as a rheostat - so turning it down it will behave as the original Martin Jones circuit.
 

pacoarcade

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New version ready featuring lateral pads for tidier connections and better placement of decoupling capacitors. BOM is inside the zip file.
 

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