Analogue-sequencer

Andy,

Thanks for the help you've been giving Fred so far.
I haven't really got anything to add beyond what you've already 
suggested, other than to confirm that D1 can be omitted and I 
usually don't fit it myself. I've heard of 78xx series regulators 
failing in such a way as to pass the input voltage directly to the 
output, which is what D1 will prevent. But I've never seen a 
regulator fail that way myself.

Cheers,
Colin f


--- In analogue-sequencer@yahoogroups.com, "Andy Wilson" <andy@t...> 
wrote:
> 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@t...