Bugger bugger bugger! I always do that! I forget the voltage drop across the LED. I shall write it out 100 times. That makes it 2.65 mA with my 680R resistors or 3.5 mA with the schematic's 510R resistors. Thanks Pr0f. Cheers, Norm. I think we all forget to do that ;-) I get lazy and use an app cal...

that 680 ohms doesn't take into account any voltage drop on the LED So you should be ok - as most led's won't light until they dropped at leat 1.5 v which halves your current

Happy Birthday to "Sinclair Society" - hope the day brings many good things.

I use to have all sorts of issues desoldering - until I hit on a method and a tool that seems to work for me. 1) Old solder - often the solder joints on the board are not keen to 'free up and flow', but a little extra new solder can help no end to promote good repair work - and that's before you rem...

This is for the 'toastrack' 128K - the one with the heatsink on the side of it. It gives the spectrum a full editing keypad - the code to drive it is already in the ROM.

This is a video from one of the guys on here showing the reset and classic startup speckle pattern at 5:47

https://youtu.be/61TCPEPBsBE

The RAM test display is just a green / white / red and black randomish pixel spread - covering the whole screen - the RAM is 128K in a standard QL, and the display sits in the bottom 32K of that memory. The ZX8301 takes the data it reads from RAM to produce the display - nothing intelligent will app...

The reason a display is possible, is that the CPU is mostly running code from the Eprom - as long as the sync signals are being sent to the monitor/TV, then you should get stable video - if you get data to make up the pixels - even if incomplete - it should still build a picture of some sort. The RA...

It's not so easy without a scope, but the following *may* work. The outputs from the 8301 ULA are TTL level, and go directly to the 8 pin Monitor connector on the back of the QL. If you display a white image which drives all three colour signals most of the time, you could check using a multimeter o...

Many thanks