The Sinclair QL Forum

My bits have arrived to put the power supply / video adaptor board together - so that will be done this weekend - the box is big enough to accommodate a 3.5" floppy - and I found my 5V only TEAC 1M floppy drive so that will be pressed back into service for the OPD. Next steps: Test the PSU / VI...

I'd certainly like to attend - as long as it's not one of the 5 weekends I have to work, or one of the few weekends I am away on holiday.


The last ever event I attended was a Computer fair in London with a reasonable QL presence - and that was back in the eighties!

There were some second source makers for these chips - such as VLSI - VL1772 - and I think there was a couple of versions that were practically interchangeable too 1771 if memory serves.

On some of the retro brew projects I've seen those as low as 300 Ohms - but that's with a different floppy controller that drives quite a high current - the LS TTL chips are probably not going to want to see that low a load. I suspect the decoupling capacitors should be 100nF as that's almost a stan...

It's just I seem to have more of them than the 1.44MB variety - lol

Derek_Stewart wrote: ↑Fri Jan 12, 2024 2:31 pm Hi,

Do you have the main board schematics, maybe a a new PCB could be made.

Derek - Stephen posted the KiCad files in the thread earlier But note the issue with the clock generator and fix for this.

time to unearth my stash of 3.5" DD floppy drives I am sure I've got some 5v only ones too - unless they are HD, not that I would try and power the drive from the dongle, but I am thinking of putting the floppy in the box I use for the power supply and QLPICO VGA interface.

Thanks Stephen - I shall download that later and have a look at the code. I noticed that in circuit - the DDEN pin is grounded on the WD1772, in QL disk interface designs - this is often fed from a latch so the density can be controlled - do you know off hand what density this interace uses - is it ...

I was thinking about the possibility of reduction - I think you could get away with:

Crystal oscilator
WD1772
A GAL - possibly even just 16V8 size
An LS240 or equival(for buffering disk drive signals)
An Eprom / Flash
An LS174 / LS175 latch

It's teasing my brain now

Many thanks for sharing this and the hard work in reverse engineering it.

Do you have the ROM code available?