QL-VGA v2

[Derek_Stewart]

Hi,

Is there an explanation of the modifications detailed in the picture.

[bwinkel67]

That's what my board looks like...crazy US motherboards. I'm assuming this all had to do with FCC regulations?!?

Edit: Well, my RAM chips don't have those resistors across them...

[Derek_Stewart]

That's what my board looks like...crazy US motherboards. I'm assuming this all had to do with FCC regulations?!?

Edit: Well, my RAM chips don't have those resistors across them...

Hi,

They are decoupling capacitors to probably give a smoother ram supply voltage.

I meant the IC just above the ram chips.

[varmfskii]

Is the picture static or does it change over time?

The distorted sections of the screen (at least at their edges) shimmer between adjacent pixel values. It is very much like the pixels go in and out of sync a few times for every scan line.

[varmfskii]

I'm still not sure what to make of it. QL-VGA v2 can handle pixel clocks from 9.976 to 10.024 MHz, so even if the crystal is way off it should cope. But then in your example picture we see that the lines are complete, which I think means that the correct clock is detected. It looks more like a frequency jitter within the line that I've never seen before this way. Does your QL also have the 74HC daughter board modification as seen in the picture here?


All the best, Marcel

Some of the bodges are present. The ones on the RAM definitely are not.
I'm pretty sure there is no daughter board in there.
I'm also guess in diodes are there to minimize the likely-hood of frying the 8301.

[varmfskii]

Sorry opening up the machine, there is definitely a daughter board in place.

[mk79]

Is there an explanation of the modifications detailed in the picture.

The grainy picture is the only thing I have on it, US QLs are still somewhat under-described. But seeing that there is one 74 logic gate of some sorts with 2 resistors and the upper two wires being connected to the crystal I guess it's a standard "logic gate crystal oscillators" circuit. But as for why it is there, I don't have the foggiest idea.

Sorry opening up the machine, there is definitely a daughter board in place.

Do you have a soldering iron and are you adventurous enough to disconnect the upper two wires from the QL board? Should be easy enough to re-attach after the fact. The lower wires are just for power as far as I can see and can stay. The upper wires are directly connected to the crystal, so it does mess with the clock in some way.

If not I can only offer you some refund deal of some sorts, I guess. Without access to such a machine it's basically impossible for me to develop for it.

[bwinkel67]

Without access to such a machine it's basically impossible for me to develop for it.

Dave just bought a working US QL, maybe you can work with him to see if he can figure out what's going on.

[varmfskii]

Do you have a soldering iron and are you adventurous enough to disconnect the upper two wires from the QL board? Should be easy enough to re-attach after the fact. The lower wires are just for power as far as I can see and can stay. The upper wires are directly connected to the crystal, so it does mess with the clock in some way.

If not I can only offer you some refund deal of some sorts, I guess. Without access to such a machine it's basically impossible for me to develop for it.

I am reasonably handy with a soldering iron. I'll try that. What does the 74HC mod do?

[mk79]

I am reasonably handy with a soldering iron. I'll try that. What does the 74HC mod do?

Well, I've yet to meet somebody who knows, nobody has ever documented it. If it is what I think it is (again, I only know the one grainy photo) it's technically redundant, like Bwinkel my guess would be that it was due to some FCC thing. But fact is no QL outside of the US has this modification and they all work fine. And QL-VGA was tested with well over 50 very different QLs without any problems, so it would be interesting to see what disabling it will change. Thanks in advance for trying