Analogue-sequencer

On 14 Apr 2004 at 18:14, blip wrote:

> hi all...

Hi Fred,
> 
> so i took all of my ICs out of the board. the regulator now gives me a
> very consistent -.326V from input (neg probe) to output (pos probe). from
> ground to either input or output, i get 0V. i'm getting 9.5V across D6.

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.
> 
> so the problem appears *not* to be an IC... what on earth could it be???
> F1 is just a wire now, and D1 has been removed completely.
> 
> hmmm... i just tried something... with the power completely disconnected,
> i'm getting -.326V from the regulator input to its output... is D1
> supposed to have a wire link or something??? the picture of the completely
> populated board on colin's site completely omits that diode.

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.

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.

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.
> 
> somehow, the power seems not to be getting to the regulator at all... it's
> getting through D6, but not into the regulator. there is plenty of solder
> on the input pin, so the only thing i can think of is that somehow in
> replacing the regulator, solder flux covered the through-hole plating and
> some of the external track and thus the power's not getting from the track
> to the pin... does that sound possible??? if so? how do i go about fixing
> it?

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

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.

The wall wart I'm using is rated at 9VDC 1A. The off-load voltage output of this is 
actually 14.8V. In my circuit, I have installed fuse F1, and Zener diode D1.

Now, with the wall wart plugged in, and power turned on here are the voltages at 
various points referenced to  the anode of D1, my 0V reference point.

F1 input +13.1V
D6 anode +13.0V
D6 cathode (Striped end) +12.2V
Regulator input (Leftmost pin) +12.2V
Regulator Ground pin (middle pin) 0.0V
Regulator output pin (right most pin) +4.99V
Zener D1 Cathode +4.99V
Battery VB +ve +3.3V

Hope some of this helps.

Good luck

Andy

--
Andy Wilson
http://www.techman.synth.net
mailto:andy@techman.synth.net