More circuit help required please

Adrian Graham witchy at
Sun Jan 8 08:00:04 CST 2017

On 08/01/2017 07:31, "Tony Duell" <ard.p850ug1 at> wrote:

> On Sat, Jan 7, 2017 at 11:37 PM, Adrian Graham
> <witchy at> 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:
>> ...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.

Thanks for looking!

Binary Dinosaurs creator/curator - the UK's biggest private home computer

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