On 08/01/2017 07:31, "Tony Duell" <ard.p850...@gmail.com> wrote:
> On Sat, Jan 7, 2017 at 11:37 PM, Adrian Graham > <wit...@binarydinosaurs.co.uk> wrote: >> Evening all, >> >> I wish I had the ability to take a board layout and turn it into a logically >> laid out schematic but as yet I don't. Video sync on my Executel 3910 is >> still running me round in circles so could one of you fine folk take a look >> at this board layout drawn as best I can: >> >> http://www.binarydinosaurs.co.uk/STCExecutelSyncCircuit.jpg >> >> ...and let me know what it does please? The chip on the left is a Plessey > > > I don't believe it's correct as drawn. For one thing you have V333, an NPN > transistor, with the collector grounded (and no -ve supplies on the circuit. > For > another, R322 is ridiculously low. And I would expect the anodes of the > 3 diodes on the RGB outputs to go somewhere other than a resistor to > ground. You were right, I'd drawn out R335 wrongly and flipped V333. All the anodes go via R312 to the collector of V333 along with R309-R311. Base for V333 is the inverted sync output of the MR9735. R322 is 6.8k (blue-grey-black-brown). All diodes are 1N4148. http://www.binarydinosaurs.co.uk/STCExecutelSyncCircuit2.jpg Thanks for looking! -- Adrian/Witchy Binary Dinosaurs creator/curator Www.binarydinosaurs.co.uk - the UK's biggest private home computer collection?