The Sinclair QL Forum

What about the MC1489.

Have you checked the plus and minus 12 volts inside the machine are OK.

Can you use the RetroModem in the other serial port? You might have to do some rewiring of the signal cables and alter the software you are using.

Martin_Head wrote: Sat Sep 28, 2024 11:31 am What about the MC1489.

Have you checked the plus and minus 12 volts inside the machine are OK.

Can you use the RetroModem in the other serial port? You might have to do some rewiring of the signal cables and alter the software you are using.

Hi Martin,

Have ordered some MC1489, so will try one of those

(Don't really want to poke around inside a live machine to check voltages, for now at least, I'll most likely make things worse if I get the hand shakes while doing it)

Will see if I can try the modem on SER1 in the meantime, I think I have an adapter for SER1

Many thanks
Tony

Based on what I have read on here and Dilwyn's site I rewired a SER2 adapter by just swapping the RxD & TxD lines at one end of my adaptor cable and plugged into SER1

When I launched QLTERM I got nothing on SER1, but on SER2 (nothing connected) I got a constant stream of blank (space?) characters

Don't know if this means anything useful please? Maybe it just means I've misunderstood the re-wiring?

Many thanks
Tony

Hi,

I use this SER2 cable connections to a Simulant Wifi Modem
For modem use on SER1 interchange 2 & 3, 4 & 5

Another point, the DTR on the the QL, is actually a CTS, according various manuals I have read, e.g. QTPI

Derek_Stewart wrote: Sat Sep 28, 2024 5:55 pm Hi,

I use this SER2 cable connections to a Simulant Wifi Modem

Code: Select all

QL SER2     DB25      DB9
1 GND       7 GND     5 GND 
2 TXD       2 TXD     3 TXD
3 RXD       3 RXD     2 RXD 
4 DTR       4 RTS     7 RTS 
5 CTS       5 CTS     8 CTS

For modem use on SER1 interchange 2 & 3, 4 & 5

Another point, the DTR on the the QL, is actually a CTS, according various manuals I have read, e.g. QTPI

Thanks. I'll swap the 4 & 5 and try again

Many thanks

With the other leads switched I have:

SER1: Modem attached but no response

SER2: Nothing attached but getting the characters (instead of blank spaces) from my first post (not exactly identical but pretty close)

Guess the next thing to try is the MC1489 when they arrive

Many thanks

Fitted the MC1489 and no difference

So that's the ZX8301/ZX8302/MC1488 & MC1489 replaced

I think I'll just break for spares as spent too much time on it, saves me having to replace the Molex keyboard connectors anyway (maybe the fully working MDV1 can be swapped into the 68K/OS machine to replace the non-formatting MDV2)

Many thanks

I was just using this machine to capture the MDV signals for something and discovered that when it's now attached to SCART the screen is rock solid in it's position on screen but a blank band, about half a screen height in size, scrolls down from the top, off the bottom and on again at the top (comes back in at the top as it starts to scroll off the bottom). So you can only see about half the screen at any one time. It takes 3 or 4 seconds I guess to do a complete circuit.

But when I use a VGA adapter the screen is perfect

Tried the SCART on another QL and it works fine with that

Maybe I shorted something swapping the serial chips

A couple of images

Hi t0nyt !

That is a new one on me, for sure!

Whilst it wouldn't relate to the earlier problems you shared, one thought that comes to mind is the generation of the 'Composite Video' signal at the QL monitor socket.

It wouldn't be used directly, but some QL to SCART plug wiring use this signal to generate the low, but non zero, voltage required by some SCART inputs on the BLANKING pin (or is it the FUNCTION pin, can't remember...)

If the transistor used in the QL to combine the weighted RGB + CSYNC signals is kaput, that might trigger some odd behaviour.

The VGA adapter wont use that signal and instead uses the raw TTL RGB and CSYNC signals directly.

Anyhow, just a thought...

Good luck!