Search found 624 matches

by Pr0f
Wed Jun 03, 2020 6:23 pm
Forum: The Off-Topic Section
Topic: Today I Received...
Replies: 271
Views: 28831

Re: Today I Received...

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...
by Pr0f
Wed Jun 03, 2020 3:31 pm
Forum: The Off-Topic Section
Topic: Today I Received...
Replies: 271
Views: 28831

Re: Today I Received...

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
by Pr0f
Mon Jun 01, 2020 9:00 am
Forum: The Off-Topic Section
Topic: Happy Birthday!
Replies: 267
Views: 81997

Re: Happy Birthday!

Happy Birthday to "Sinclair Society" - hope the day brings many good things. :D
by Pr0f
Sun May 31, 2020 9:11 am
Forum: Hardware
Topic: Issue 6 VM12 & resistors confusion
Replies: 79
Views: 4337

Re: Issue 6 VM12 & resistors confusion

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...
by Pr0f
Wed May 27, 2020 10:13 pm
Forum: Hardware
Topic: I haven't seen one of these before.
Replies: 7
Views: 448

Re: I haven't seen one of these before.

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.
by Pr0f
Sat May 23, 2020 11:14 pm
Forum: Hardware
Topic: Issue 6 VM12 & resistors confusion
Replies: 79
Views: 4337

Re: Issue 6 VM12 & resistors confusion

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
by Pr0f
Sat May 23, 2020 10:56 pm
Forum: Hardware
Topic: Issue 6 VM12 & resistors confusion
Replies: 79
Views: 4337

Re: Issue 6 VM12 & resistors confusion

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...
by Pr0f
Sat May 23, 2020 9:21 pm
Forum: Hardware
Topic: Issue 6 VM12 & resistors confusion
Replies: 79
Views: 4337

Re: Issue 6 VM12 & resistors confusion

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...
by Pr0f
Thu May 21, 2020 10:31 am
Forum: Hardware
Topic: QL Video issue - Red color missing
Replies: 16
Views: 3493

Re: QL Video issue - Red color missing

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...
by Pr0f
Sun May 17, 2020 11:08 pm
Forum: Hardware
Topic: QL Eprom programmer
Replies: 36
Views: 7175

Re: QL Eprom programmer

Many thanks :-)