Making progress here.
Did as I just said... pulled my bread board and added buffers to the H/V signals.
At first with a TTL chip.... got only 4.4V at the output, bummer.... then light bulb.. ah yeah I am rusty, TTL outputs have never been able of 5V to begin with.. there is a diode to Vcc internally, the best you can hope for is 4.4V or something, and that's what I get.
So instead I used a 74HCT chip, a 244 8 bit bus driver, because that's what I had.... not I get 5V at the output. Well, the first chip I used was defective, was doing strange things... the second chip was the winner.
Plugged the wiring harness to the video board. Amplitude drops a bit but not much. Most notably the leading edge of the 15kHz signal is now quite rounded, see pic.
The rising edge looks good for the most part, but the very top of it, between 4 and 5V, is quite rounded.
That's when I was scoping on the breadboard. I then scoped straight on the video board connector in case all that spaghetti wiring were degrading the signals badly... but no. Signals look exactly the same no matter where you look.
I got curious and searched which one of the millions SMD passives the H/V signals were connected to, on the board.
See pic. There is a long row of passives between the connector and the video chip.
I scoped these passives and quickly found where the H/V signals were routed to.
They go each to a 1K resistor. My signals get to one side of the resistors just fine, 5Volts, however on the other side, where it buggers off to the chip, the amplitude drops to 4V. Hope that's OK for the chip.
Anyway, signals had at last a proper amplitude, so I fired up everything...
... and we have improvement !
Now the board can detect something ! It can't make sense of it though, so it keeps cycling endlessly, displaying various kinds of garbage, but GREEN garbage which is promising since I used the green colour channel... so clearly it's seeing my signal now, no doubt about that.
It cycles between 3 states mostly, from what I can see :
1) A solid green screen filling the entire screen.
2) long pause with a black screen.. probably it's thinking hard on what to do next
3) A "half solid" green screen... looks like a fine mesh, a woven fabric, something like that...
4) long pause with a black screen again
5) Now the interesting bit. On this part of its cycle, it displays a black screen with some green garbage flying by, that looks like it contains valid data, but garbled in the way you get when there is a timing issue.
Whenever it displays this, it lasts for a split second, half a second if even that, so my brain doesn't even have time to absorb what it's seeing... but after repeating the cycle many times (you never get the exact same garbage twice of course, depends on the pot luck of the timing at that particular time), I am 100% certain it displays intelligible ASCII text, and some geometrical shapes.
It displays a row of horizontal rectangles, just the outline of them, like you would expect from a status bar displaying place holders for menu options, and you would press function keys on the K/B to activate this or that menu option. That pleases me, it adds up.
All these rectangles are empty but sometimes I see one that has text in it (no time to read what it says though), in reverse video. So that's perfect, I like that a lot.
Also, on the next line, right below this line of rectangles, it displays some more text, a couple of words : " REMOTE "... followed by another word but I am not 100% sure what it is. Maybe " REMOTE CONTROL ".
Again I like that, because we know that the big brother of this programmer, once it's booted, gives you the choice of being used either remotely via a desktop computer, or locally using the K/B attached to one of its serial ports at the back.
So it all adds up nicely.
So the board clearly can make "some" sense of my video signals to display something interesting.... but it's not clever enough to get the timing 100% right.
Two possibilities here I guess :
- The programmer indeed uses non standard signals, some custom variation of CGA, but not compatible with off the shelf CGA monitors... just so that they could force you into buying their own, expensive of course, monitor...
- The board is defective. Indeed, it just keeps crashing and crashing and crashing. It's a disaster. Every time I power it up, I do get the chinese "splash scree" while its booting, then a black screen, and from there it's pot luck : half of the time the buttons won't be responsive and I can't enter the on-screen menu. Other times menu will work, but then when I exit it and try to use the SW and AUTO buttons... they won't be responding.. so as a quick sanity check I press the MENU button to see if the board is still alive and... most of the time it's not, menu doesn't work any more.
It's a disaster.
So I guess I could try to get a new board under warranty, see if that's any better.
I guess it's also now time to read the 5 pages of messages on that French forum I was pointed to at the beginning of this saga, where a few people discuss their programmer, the big brother of mine. Maybe they talk about the display... and if not, I could post a message about it.
https://forum.system-cfg.com/viewtopic.php?t=5743So I am making progress eh, what do you say ?!
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