OSI Klyball build problems

[Reggraham]

I have successfully built the OS SBII replica using the Klyball pcb however there are some weird problems I am experiencing
The only monitors I have available these days are HD TFT screens I use with my Desktop PC's and Macs. One is VGA+HDMI the other is Displayport (mini and full size) + HDMI both are 1920 x 1080 displays.
I have purchased multiple Composite Video to HDMI interfaces and one Composite Video to VGA, it would not sync.
I found on an Australian site a simple single transistor output stage with a 75ohm resistor which cured that persons problem, it made a small improvement I change the resistor to a 10ohm which then allow it to sync but really unreliably. I then purchased a video amplifier and this has improved it a lot but it still needs adjusting every time I start the board.
I was originally using the CEGMON OSI monitor ROM and the D/C/W/M prompt was never on display I always had to enter the RAM etc so I could then adjust sync.
I changed to the SJGMON and this is much improved I always see the C/W/M prompt but still have to adjust sync most of the time.
I built a couple of test amps but no improvement, I can only assume it's the horizontal sync frequency of 15.360Khz that my monitors cannot handle, I have a 4.5inch Car Cam video monitor which works OK on an Apple II displays nothing for the SBII. I am almost certain I have timing issues as I get random '(' characters on the screen.
Is anyone else experiencing these problems and if so a fix?

[ronin47]

I did have a few sync issues with mine, plus a few other video and other weird problems, my build thread is here: viewtopic.php?t=845

I don't know if it'll help, but it may be worth a read.

I added a single transistor buffer to mine so I have both standard and buffered composite.

IMG20250110132333.jpg (3.18 MiB) Viewed 11368 times

I do find that some screens work fine and others are tetchy, I only have one CRT with composite, a 5 inch B&W display and that seems OK, but for some of my other composite displays the sync isn't great, though it may be because my displays are mostly PAL and IIRC the Klyball replica uses NTSC composite. Someone please correct me if I have that wrong.

Adjustment of R58 did help me quite a bit.

[HOWARDHB]

What crystal have you installed?
It should be 3.93216 Mhz
All the video timing is derived from it.

I tried a 4.0 Mhz crystal on my 600D, and the video was terrible.

Also, I had "issues" with those little ceramic disc caps, as their value tollerance seems to be very "wide".
(they're fine for decoupling, but not for "timing")

H.

[bxdanny]

I was also thinking that, if you think the problem is an incorrect video frequency, then changing the main timing crystal on the board could fix that. If you want the horizontal frequency to match the NTSC standard as closely as possible, then you should order a custom crystal of 4.027972 MHz. The horizontal frequency will then match the NTSC standard of 15,750/1.001 or about 15,734.3 Hz extremely closely. (The CPU clock will run at about 1.007 MHz, but that really should not be a problem.) However, the vertical frequency will be way off, at about 61.46 Hz.

The original crystal used by OSI was, as Howard says, 3.93216 MHz. It produced a vertical frequency of exactly 60 Hz, but a horizontal frequency, as you mentioned, of 15,360. So it's really a question of which your converter devices can handle better, errors in the vertical frequency or the horizontal. A crystal of 4 MHz even actually produces something of a compromise, with a horizontal frequency of 15,625 and a vertical frequency of about 61.035 Hz. That might be good enough to produce a stable display with your converter device. (Or it might not. It depends on the monitor.)

The real problem with OSI's video circuits is that the ratio of the horizontal to the vertical frequency is just 256:1, instead of the 262:1 produced by most other home computers, or the 262.5:1 of true NTSC interlaced video. A few years ago, someone posted here about a Superboard that had been converted to produce PAL-compatible 625-line, 50 Hz video. I can't seem to find that now, but the basic idea was to insert some extra blank lines after each vertical retrace, with the counters that address the video RAM stopped until the desired number of blank lines had been reached. I'm wondering whether something like that would work in this case. You would want to add six blank lines after vertical retrace, so that there would be a total of 262 lines per frame/field. The optimal crystal frequency would still be 4,027,972 Hz. But before trying anything like that, try just changing the crystal in the standard circuit, first to 4 MHz even and, if that doesn't work well enough, then to the one I just mentioned in the previous sentence.

[Reggraham]

I got fed up with trying different adapters on my HD monitors so in the end I purchased a cheap 10inch aft monitor on AliExpress, it has several input include BNC, RCA composite with sound, HDMI and VGA it only cost £29 weirdest thing is it syncs perfectly so that has solved that problem. I have tested it with and without an external driver transistor and it works either way.
If anyone is interested and needs a small monitor for working with vintage computers this is the link below.
https://www.aliexpress.com/item/1005007 ... 1802KXMj7k

[Thomas]

This specific monitor is sold under different brand names and actually works pretty well, also with other vintage computers and composite signals. The one I use is from Podofo.

Podofo.JPG (40.01 KiB) Viewed 11222 times

My only concern slash warning is the dodgy power supply, which should not be used. It is one of the lethal power supplies from Chinese production with a none to nothing insulation form main to the 12V. Replace it with a proper quality PSU, if you don’t what to risk your life.

[ronin47]

This specific monitor is sold under different brand names and actually works pretty well, also with other vintage computers and composite signals. The one I use is from Podofo.
Podofo.JPG

My only concern slash warning is the dodgy power supply, which should not be used. It is one of the lethal power supplies from Chinese production with a none to nothing insulation form main to the 12V. Replace it with a proper quality PSU, if you don’t what to risk your life.

This is the exact display I have. Works a treat, but I gave it my own PSU.

BTW I am using a 4Mhz crystal exactly.