Color Classic analog board re-design, needs community feedback.

Good job. In your schematic you marked DL1 as BZX84-C8V2 which is a 8.2V zener diode. I also checked the schematic made by @jonschultz which marked DL1 as BZX84-B36, a 36V zener diode. Which one did you use to get it working?

Also seems XC1186B does have xray protection, DL3 is fed by a sensing winding in flyback transformer, if HV is too high (higher than zener voltage of DL1), pin 30 will be pulled high and trigger xray protection. Never noticed this circuit before, and don't think it's causing issue with 84V VGA mod. What's your voltage reading on TP27 and TP37 when it's powered on by the way?



Also regarding the hourglass distortion and horizontal width, if you can't stretch the image wide enough, try to add a high voltage capacitor at CL26 right next to HOT. I can increase horizontal width to fill the whole tube without hourglass distortion in the middle by adding a HV capacitor around 3.3-4.7nf. You can also increase +B a little bit to get more horizontal width but it also changes geometry settings.

Good luck.

It's been a long time since I last looked at that zener, but I believe it is indeed a 36V part. My indication of of x-ray detection on the associated input on the XC1186B is mostly by supposition, since I observed that it will indeed kill the horizontal deflection if an injected voltage on the cathode is too high and the zener conducts. Also, other "jungle" chips have an "x-ray" input that serves this function. Lately, I've been doing a lot of measurement on the pin 35 position, as I'm rev'ing my XC1186B reverse-engineered circuitry to use the flyback input for phase correction, and the peak of the pulse there is about 2V (using the 68V VGA-mod B+). That means nominal voltage at the DL1 cathode is probably around 20V. The zener voltage has to be higher than that to prevent x-ray shutdown. I would expect the voltage to scale more or less linearly with the B+.

ArjenCNX said:

GOOD NEWS!

Thanks to mark_W, i found that i had the wrong value for DL1, the zener diode that protects in case of over voltage, once i placed it over from the orignal board, the unit started up and i have display now! still adjustments need to be done, geometry is not good yet, and neither is color, but im sure this can be adjusted/fixed!!!! Big day!

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Congrats! That's great!

ArjenCNX said:

yeah man! so, indeed CL26 will be added, probably around 3nF, vertical image size right now is barely adjustable so ill find the cause of that as well, and then ill go over the board and optimize some more, i would like to replace some parts with SMD ones if possible, ive got some more jumpers to replace, and i really hope at some point we can integrate your XC1186B solution on the same board design. once im done ill share the Kicad files here, so you can have a look and recommend things there as well.

Seems we will get that replacement analog board after all!

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Sounds great. If you might consider socketing your XC1186B on this particular board, then you could swap in mine for initial testing. I’d be happy to send one to you, but it might take a little time (I only have one v3 board with a lot of rework). I’m trying to finish up v4 changes, and I’m still fabbing protos by milling. Full integration at some point would be amazing, thanks for the consideration!

ArjenCNX said:

Also, i had the idea to integrate HDMI out at some point, im looking for suitable IC's for that that can take the RGB+sync signal and spit out HDMI out the back.

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Seems very doable with a VGA-to-HDMI converter, which you can probably find in IC form. The main challenge would be dealing with the CC’s composite sync, as it doesn’t natively produce independent VSYNC and HSYNC signals, like standard VGA. I use the LM1881 on my board to pull out VSYNC, and generate my own HSYNC with discretes (though, it might not necessarily conform to the VGA standard). So the signals are there, it just might require a little signal conditioning.