Search found 1349 matches

by Pr0f
Sat May 25, 2024 2:11 pm
Forum: Hardware
Topic: Faulty (video) ram
Replies: 25
Views: 1422

Re: Faulty (video) ram

Well done on the progress with the DRAMS - so now probably just a single faulty chip?
by Pr0f
Sat May 25, 2024 2:11 pm
Forum: Hardware
Topic: Faulty (video) ram
Replies: 25
Views: 1422

The QL motherboard has pin 1 and pin 28 wired to 5V - so the 'expected' A15 signal is not on that pin - instead it's used as a chip select for the ROM's - the ROM's in the QL ROM set - one is active high and one active low - so A15 decodes whether lower 32K or upper 16K rom are selected. Either ROM ...
by Pr0f
Wed May 22, 2024 9:14 pm
Forum: Hardware
Topic: Faulty (video) ram
Replies: 25
Views: 1422

Re: Faulty (video) ram

that could be down to either a ram chip not being writable (Data in on the RAM shorted or open circuit), or to a shorted or open address line on the DRAM chips - the regular pattern also suggests something like this. Such problems are hard to find. As you have surmised - the upper and lower banks ar...
by Pr0f
Mon May 20, 2024 11:28 pm
Forum: General QL Chat
Topic: Anouncement for the 40th Anniversary of the Sinclair QL in Dormagen (Germany)
Replies: 50
Views: 9556

Re: Anouncement for the 40th Anniversary of the Sinclair QL in Dormagen (Germany)

those current draws are favourable. Letterbox - just that a keyboard and LCD screen combo may be a good way to do this - as it's one single case to make - no hinges. The letterbox LCD screens are available with HDMI input - but the resolutions are a bit strange - they are usually 400x1280 or 480x192...
by Pr0f
Mon May 20, 2024 9:26 pm
Forum: General QL Chat
Topic: Anouncement for the 40th Anniversary of the Sinclair QL in Dormagen (Germany)
Replies: 50
Views: 9556

Re: Anouncement for the 40th Anniversary of the Sinclair QL in Dormagen (Germany)

Thoughts from the 40th QL Celebration. It was a late decision for me to attend the 40th Anniversary celebration in Dormagen, but I am glad that I did make that decision. Having been in and out QL ownership over most of those years, but strangely always having a couple of Sinclair products in my hous...
by Pr0f
Mon May 20, 2024 8:51 pm
Forum: The Off-Topic Section
Topic: Z88 power supply
Replies: 15
Views: 1209

Re: Z88 power supply

I've used 7V without a problem, not sure about 7.5V - It is dropped by one diode forward voltage (about 0.6-0.7 vols), and feeds the circuit that would normally see the 6V from the batteries. Very fresh batteries could provide close to 1.6V each - giving a voltage of 6.4 against the 6.9 you would se...
by Pr0f
Mon May 20, 2024 8:48 pm
Forum: The Off-Topic Section
Topic: Z88 power supply
Replies: 15
Views: 1209

Re: Z88 power supply

The Z88 does have it's own rather clever little power supply that can produce a bit of high pitch wine when operating - usually caused by the small ferrite transformer / inductor on the board being a tiny bit loose. Sometimes a small blob of silicon sealant on it can anchor it to the PCB sufficientl...
by Pr0f
Sun May 19, 2024 11:06 pm
Forum: QL Emulation
Topic: A small QL
Replies: 70
Views: 12126

Re: A small QL

I think you've done a great job getting the q68's out to so many Derek, it's attracted a good few people back to the QL scene!
by Pr0f
Sun May 19, 2024 6:11 pm
Forum: QL Emulation
Topic: A small QL
Replies: 70
Views: 12126

Re: A small QL

I got one of those kits to see what the dev tools were like. It seems there are a good few design constraints on the pins, so what looks like a lot of pins soon gets eaten up with the dev board resources. I've seen the 20k used to define the Yamaha MSX2 chip, but Peter gets a video controller, a mem...
by Pr0f
Sun May 19, 2024 2:22 pm
Forum: General QL Chat
Topic: Anouncement for the 40th Anniversary of the Sinclair QL in Dormagen (Germany)
Replies: 50
Views: 9556

Re: Anouncement for the 40th Anniversary of the Sinclair QL in Dormagen (Germany)

Thanks Martin, I echo your sentiments about the organisation at relatively short notice, and putting faces to many contributors I see posting on this forum. It was an excellent weekend and I even managed to avoid the bad weather. I will post something more complete tomorrow when I am on a computer r...