QL Pico VGA

[bola_dor]

Well I reviewed all connections, cleaned up the board looking for any flux residue.. added the rgb gnd connections to the dsub15 output (my old CRT doesn't like any pins soldered together) then wrapped anything whith tape and then aluminum foil with a wire I soldered to the db15 metal case and to gnd.. from the QL exit to the VGA cable ..
Nothing changed.
Tried another monitor... neither..

(Tap to see it in motion)
I am using firmware v0.05
Sometimes it showed this screen

[Peter]

Wires from QL are not shieded but about 7cm long, I guess they are short enough.

Yes, at this short length, lack of shield can not explain your problems.
I don't use the large module, so I can not try the same firmware as you.
What QL are you using? Not that you have a 60 Hz output...

[Maskenlos]

I decided to remove this post as I can not re-check the scope setting. I currently do not have access to the scope and the QL board.

Stephan

[Peter]

Once playing around with the ZX8301 replacement I found that the QL output level is about 0.7V peak peak.

Just 0.7V would be totally wrong. It must be TTL levels, otherwise the converter can not work properly.

[Maskenlos]

.

[Peter]

For me it is still worth to check the input level of the converter from Bola and share this information.

Yes absolutely. And the QL variant.

[tofro]

0.7V would be about OKish for composite. But not for RGB, which must be TTL, as Peter has said, and that picture doesn't really look like a composite signal.

[bola_dor]

Hi all,
Mine is a UK, 50Hz ISS 7 QL.
I have a humble hanheld oscilloscope that I hope is good enough for this.
I measured the QL output at the cable adaptor end without the Pico connected..
Signals are TTL level.. perhaps a bit high?
I did ground the probe to the composite output with a perhaps too large cable so signal quality may not be great but I didn't what to risk a short at the ULA output using the same db9 GND.

This is red channel (all three looks sumilar)

And CSync

Now the outputs:

Horizontal Sync is at 48Khz, is that right?
VSYNC at 60Hz I think is OK.


Output channel levels are about 4v.. isn't that too high vor a VGA? monitor whas attached and on at that moment..

[attachment=1]20230318_185514.jpg[/attachment

[Maskenlos]

Hi Ernesto,

thanks for the reply.
The red output looks good to me!
Could you measure the red channel with the adapter attached?
On time on the output of the QL and second time on the input of Raspberry board?

Thanks.

Stephan

[Peter]

Output channel levels are about 4v.. isn't that too high vor a VGA?

If "output channel levels are about 4V" means RGB signals: Much too high. Did you forget the output resistors? Together with the termination resistors inside the monitor, they scale down the output voltage. Or did you measure at the wrong point?

If "output channel levels are about 4V" means only sync signals: Probably okay.

Still, your problem looks more input related to me, as you seem to get a stable "blue srceen" display. Maybe wrong circuit built, wrong resistor values, or you have damaged your module already. I'm not sure those tinkering problems should be discussed in such a length here, as nobody else has them. A seperate thread might be better, so the actual infos about the QL Pico VGA do not go down in all these posts.