Electronics > Repair
Vintage chip Programmer : " Micropross ROM 3000U "
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pcprogrammer:
Hi Vince,

good work. You found the video levels for VGA too, and a restive divider will work.

The video signal looks interesting and what came to my mind was some blinking cursor shown while booting.

Will be nice to see it on an actual monitor. :-+

Edit: The clicking noise on the video is that the floppy drive?
Vince:
Yes the noise in the video is the floppy drive working !
I enabled the audio in the video so you can hear it and "live" the boot process, and then match its disappearance with the change in contents of the video data.

pcprogrammer:
Hi Vince,

I forgot that in the old days we had monitors with TTL inputs, so the 4V level you are measuring is not to allow some headroom for brightness, it is just the outputs not reaching the rail.

For the VGA monitor the inputs are 75 ohms, so adding a resistor in series of 390 or 470 ohms will do. You can test it with only one of the signals, but means that what you see on screen will not be white, but the color of the input you are using.
Vince:
Thanks for that. Saw your comment just in time before I fired it up, so made that last minute change !  :-DD

Just powered it up... sadly the monitor doesn't detect a valid signal.

Took me over an hour to manage to connect the programmer to a freaking VGA cable, believe it or not !

So many things went wrong. everything. It's amazing how much can go wrong in such a simple "project" !  :wtf:
Interconnect and prototyping definitely is not as quick and easy as I would like it to be.
My "best" solution, given what I had to work with, is this fragile horrible mess.

Anyway it doesn't work, miracle don't happen so easily....

I will try to troubleshoot it but it's a pain. I think I might as well spend more time and a we bit of money, a few euros, to try to make something less convoluted/simpler, more compact, more tidy, more reliable....
Since I will be working on this programmer for months and years, I need a much more durable and reliable and less messy solution. Something I can just plug and play.
I will probably end up making a little board on Kicad and make a dedicated adapter.  Yeah, see, YET ANOTHER little sub-project inside the project..... inside the main project !  :-DD

Electronics is a fun hobby !  >:D



Vince:
OK, 1+ hour of troubleshooting later....

Found that the signals from the programmer were not making it to the breadboard...

... found out that my ugly FDD cable hack was not a good idea : the cable had already gone bad, pin #1 which carries ground, was not making it to the other end of the cable any more  ::)

So did something better, which I should have done from the get go.... used a female header strip, cut it to length / 8 ways, and soldered solid core wires (much easier to stick into the breadboard holes than the tinned super thin stranded wires of the FDD ribbon cable....) to it, which was surprisingly much easier and quicker than I thought it would be... why didn't I think of doing that in the first place rather hacking an FDD cable... brain fart I guess...
Added bonus : now that I know what signals / pins I need, I could solder only 4 wires to the female header, so much tidier than before. So  a great upgrade so to speak, see it's already improving !  ;D

Other issue I found... looks like I got the pinout wrong in my earlier post (corrected now...) ! I thought I had ground on pin #1 and #8... well I found out pin #8 actually puts out 5V !!!  :wtf:
I don't know...
So since I of course put the two "grounds" together, I was therefore shorting that 5V something to ground ! Does not help...

Anyway, I now have my signals making it to the breadboard properly, and I also scoped the video signal after the 390R resistor, and I do get about 0.7V so it's perfect  8)

So, was looking much better, so I hooked a monitor up !

Result : no signal detected !  :(

Tried another monitor.. still no signal detected, ARGH !!!  :(

Tried a third monitor, the last I have.... SIGNAL DETECTED, YES  !!!!  :box:
HOWEVER... no picture, because the monitor complains that the signal is "not optimal, I should use resolution XXX and refresh rate YYY instead ! "
FFS don't THINK stupid you, just freaking display what I am giving you !!!  :horse:

I thought OK maybe I got the Hsync and Vsync mixed up.... so I swapped them just to see. Result : fails to detect the signal.

So that means I got them right the first time and it's indeed detecting a signal.... it's just that it doesn't like the timing enough to bother trying to display that signal, bummer  >:(

I guess sub 50Hz refresh rates are so crap that the designers of the monitor thought no customer would ever be likely to be feeding such a signal !  I don't know.... can't blame them I guess.

That's the problem with LCD / modern monitors, their VGA input just can't be relied on ! It's OK to connect to a computer graphics card, or a more modern piece of TE like a digital scope with a VGA resolution, but that's about it. To ther defense I guess that precisely all they meant to achieve with this VGA port, and indeed one of my monitors calls it the " PC " input ! Says it all.

But for older / vintage stuff, you need an actual CRT monitor.. the real thing. Of course I had 3 of them up until recently but scrapped them all to make space. I knew I would regret it. It's always like that.  :palm:

I can try to use my computer's monitor, my last hope.... but not holding my breath.

I guess I will need to go get a cheap old but decent CRT monitor locally, like the ones I had. Will see what I can find within a few kms radius from home.

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