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retrogear
January 7th, 2016, 06:07 PM
Evidently Zenith Z100 9 pin color output is the same signal and pins as IBM CGA. I used the same setup to test this as I did with CGA. I used the video DAC from here:
http://bit-c128.com/ coupled to a GBS-8200 scan doubler. On the Z100 video board, I set jumpers to positive H and V sync (also not composite). This seems very stable
and sync locked in place much better than my test with IBM CGA. Zenith rocks !!!
Here is some photos using the color test in the bios and diagnostics:
28904289052890628907

Fun stuff !!!

Larry G

Chuckster_in_Jax
January 7th, 2016, 08:17 PM
Looks good. Would like to see more about this.

retrogear
January 8th, 2016, 07:17 AM
More detail. Here are pictures of my adaptors. I had trouble trying to use the wiring jack on the DAC so had to solder them on the PCB.
Possibly the wires on the wiring harness sent with the GBS-8200 were too small:
28908
Also the H+V jumper shown on the DAC needs to be in place. The 8200 requires composite sync for lower resolutions than standard vga:
28909
Here is an illustration of the Z100 video board. Remove the floppy drive holder and drives, top case, move keyboard out of the way, 3 screws on the video board
and flip up to access jumpers circled in red. Also all three video memory banks circled in green must be filled:
28910
Set J302, J304 to + for positive sync and J303 to V for separated sync (not V/C for composite).
Set J305 and J306 to RGB (not G) for color operation.

Fun stuff !!

PS - a 5V 2A DC adaptor is required. From what I've read it must be rated at least 2 amps.
Warning, the one Amazon indicated as being most purchased had the wrong plug !!
I had to manually cut wires and solder on a correct one. Can't give you a # for correct one because I don't know it ...

Larry G

Chuckster_in_Jax
January 8th, 2016, 07:34 AM
Thanks for the info! This is a project I would really like to implement. Especially since CRT's are becoming scarce.

Chuck

retrogear
January 8th, 2016, 09:00 AM
There is a faint RF noise on screen which i'm sure is coming from z100 power supply. I might try doing some ground shielding. If it improves, I'll post here

PS - can see diagonal lines in photo #3 full color bars

Larry G

new_castle_j
January 11th, 2016, 07:30 AM
There is a faint RF noise on screen which i'm sure is coming from z100 power supply. I might try doing some ground shielding. If it improves, I'll post here

PS - can see diagonal lines in photo #3 full color bars

Larry G

This is waayyyy cool!! Full color

retrogear
January 11th, 2016, 08:46 AM
Yea, check out my album pictures too. I'm not seeing any interference now that I moved things around and used normal aspect setting in my LCD and not expanded to full screen.

PS - I noticed too that my I-pad camera was picking up the screen interference that I couldn't see with my eyes so could be a digital camera is catching the conversion clock frequency somehow
which is not seen with naked eye?

PSS - or my eyes are getting old ...:)

Larry G