More circuit help required please

Tony Duell ard.p850ug1 at
Sun Jan 8 08:01:31 CST 2017

On Sun, Jan 8, 2017 at 11:10 AM, Adrian Graham
<witchy at> wrote:
> On 08/01/2017 07:31, "Tony Duell" <ard.p850ug1 at> wrote:

>> 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.
> Hm, ok, that's today's task then. For V333 it could be that I just have the
> pin numbers reversed but I'll double check. The diodes bothered me too and

No, it's more than that. The emitter returns to ground too. There is no way
of getting a voltage across colletor and emitter.

> I'm trying to think of a better way of tracing unknown lines on the bottom
> of the board. My sponge-wrapped-in-tin-foil method isn't infallible.

I've been known to test to every connection on the board. Or to desolder all the
components I know it goes to and then do resistance checks to prove it goes
somewhere else. Yes it takes a long time,but...

Knowing what to expect, what is possible, helps a lot too. But that only comes
with practice.


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