The Sinclair QL Forum

I have a CRT multi frequency monitor and a LCD monitor (14", 1280x1024), both with just (D-SUB) VGA connector and want (at least one of them) connect it to a BBQL(1)

User "dex" told me, that this is only possible with a monitor that supports 15 kHz (thank you). As I cannot find the specification for both of the monitors, I just will try it.

Question: Can I destroy the monitor or (EVEN WORSE) the QL, if I wire a cable and connect it to one of the monitors?

Which signals must be connected?

I assume QL ground to analogue ground red (VGA pin 6), green (VGA pin 7), blue (VGA pin 8), analogue ground for sync signals (pin 19) and of course QL r/g/b to VGA r/g/b .

But what's with the SYNC signals. QL has only VSYNC (vertical sync) and CSYNC (composite sync), but NO HSYNC (horizontal sync). How must the QL sync signal(s) be connected to the VGA sync signals? Wikipedia says pin 13 of VGA connector is horizontal sync OR(!) composite sync. Can I connect QL CSYNC to pin 13 (HSYNC/CSYNC) of the VGA connector (must then QL VSYNC not be connected, or must QL VSYNC and CSYNC be connected)?

I have a soldering iron, a lot of resistors, capacitors, diodes, ... and a cable (8 wires) with an 8-pin DIN plug (for QL side) with open ends :-)
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(1) BBQL: Black Box QL (i.e. an original QL)

Peter,

that's not going to work with simple wire connections.

Better have a look here: https://dilwyn2.wordpress.com/2020/02/28/ql-vga/

If you really want to go that way, check the following:

• Your Multisync must be able to synchronize with 15KHz Horizontal frequency - Most VGA (and VGA-Multisync) monitors are not able to do that, and the ones that do are notable exceptions (I have a Standard BENQ VGA TFT that will, and a NEC MultiSync TFT that won't. So much for the truth behind "Multisync" )
• You need to add some circuitry that separates the QL Composite sync signal into HSync and VSync. Consult the internet for example circuits, there are many - But nothing as simple as diodes and resistors only - You will need at least a handful of of active components or a specialized sync separator IC and a separate power supply.
• The QL outputs colour signals (R, G, and B) as binary TTL signals (0-5V) - Any VGA monitor, however, expects these signals on levels 0-0.7V, which is quite a difference. Here, you can get away with simple 330Ohms resistors in series.

If you've done all this, better don't expect a fully crisp picture - analogue circuitry will always have some sort of picture distortion.

You probably see this is not at simple as it sounds, now. Check Marcel's QL-VGA adapter, once it's available - It digitally re-synchronizes the signals to exacly what a VGA monitor wants and produces a crystal-clear picture.

Tobias