The Sinclair QL Forum

The other one comes from the NAND gate - with FC2 and the CMOS RAM enable from the ICL ULA as the inputs to the gate - so the RAM can only be accessed in supervisor mode.

I think that comes from the drain of FT5 - controlled by the powerdown on the 15 way connector, that FET will ground the /CE input when powerdown is at 5v (this signal goes to multiple places) - the drain has a load resistor connected to the diode junction from 3v lithium, and diode from 5v, so eith...

The ROMS are I think in 3 parts - the first 64K are a combined OS ROM - so that's ROM A and B ROM C has a header like other application ROM's - so I wonder if this OS Extension is handled as an application ROM - ROM D seems to be the one that may have different code in it and seems to be mostly prov...

Seems odd you get a ROM fault when it had worked before you put it into storage. I noticed that on both my daughter boards - 3 of the ROM chips are mask ROM's and the last one closest to the processor - the one that's in position '7' of the LS137 decode at address 0xA8000 - is an EPROM. It would be ...

I'm wondering if this is a fault with ZX8302 (9v battery) power circuit?

On the WD1770/WD1772 question - https://www.bing.com/ck/a?!&&p=a82800f7a09cfd2aJmltdHM9MTcwNTYyMjQwMCZpZ3VpZD0zNWNkMTA1ZS1hMmVmLTY3N2ItMTZhNC0wMzZjYTNkNzY2OTUmaW5zaWQ9NTQ5Mg&ptn=3&ver=2&hsh=3&fclid=35cd105e-a2ef-677b-16a4-036ca3d76695&psq=WD1770+WD1772+differences&u=a...

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...