Analogue-sequencer

On Thu, 15 Apr 2004, Andy Wilson wrote:

> When you say you are getting 9.5V 'across' D6 do you mean you are
> measuring voltage actually across the diode itself, or is one end of
> your probe at 0V? You should only be getting approx 0.7V 'across' D6 if
> it is forward biased. i.e. if the anode is more positive than the
> cathode (cathode's the stripey end). Have you checked that D6 is in the
> right way round? 9.5V across D6 sounds as if it's reversed biased, which
> would be why there's bugger all getting to the regulator.

both ends of my probe are on either end of the diode. i'll try measuring
the other way, with the -Ve end at ground.

also... last night i found that when the powersupply is plugged in but
switched off, i still have about 2V coming into the PCB! the only time it
goes away is when i fully unplug the PS. (and that's 2V across d6...
measuring the silly way i have been.)

> You can safely omit D1. It's there to prevent overvoltage getting to the ICs in case the
> regulator fails. A bit of belt and braces on Colin's part.

that's what i thought... thanks!

> The -0.326V is probably due to residual charge on electrolytic capacitor
> C13. BTW check that cap's in the right way round. Striped end is -ve so
> it's pointing away from the regulator.

ah, that makes sense. to my knowledge it's fine, but i'll check again to
make sure.

> Incidentally, when measuring voltage at certain points in the circuit;
> It's often more useful to take measurements with reference to ground.
> i.e. put you -ve probe on a 0V point and the +ve probe on the point you
> want to measure. For subsequent measurements, leave the -Ve probe where
> it is, and just move the +ve probe.

thanks much... i didn't know that until now. :) always glad of an
education.

> Try measuring the voltage actually on the regulator input pin itself.

i've tried this with the -Ve probe on the output of D6 with the +Ve probe
on the input pin. 0V. but maybe that's due to my measurement "technique."

> OK. In the interest of investigating this further. I have just opened up my P3. Here are
> some measurements for you reference, which I've made, all referenced to 0V.

thanks andy! my PS is 9V but i think i can adapt your measurements to see
where mine is off.

> Battery VB +ve +3.3V

that's working on mine at least. :)

> Hope some of this helps.

very much.

thanks so much, andy.

f.

bleep.
out.

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