[sdiy] DMM problems [OT]

[Harry Bissell Jr]

OK Alex...  (Trebeck - Jeopardy TV show :^)

The Final Jeopardy catagory is 
"My DMM ohms scale doesn't work"

And my question is...

What is "an input protection diode on the ohms
scale is damaged maybe due to some circuit voltage
applied... and that diode now has a reasonably
constant offset voltage... which the meter is reading
on each scale as being a ratio of the full scale
reading, plus or minus some 'who knows' factor"

I would trace that out... and look for some defective
part.

Maybe possible that a MUX chip that switches the modes
may be damaged ???

H^) harry

<blonde mode on>

uhhh...  "what is.... don't use the ohms scale ???"

</bmo>

--- Seb Francis <seb at burnit.co.uk> wrote:

> Unfortunately not this simple .. I tried different
> leads (and even just 
> shorted the terminals with a banana lead)
> 
> The interesting thing is that it gives very
> different readings in 
> different ranges:
> 
> Continuity tester mode: 31.8R + bleep
> Lowest: 32.0R
> Low: 424R
> Mid: 2.30K
> High: 20.8K
> Higher: 208K
> Highest: 0.21M
> 
> All other modes: diode tester, cap meter, voltmeter,
> etc. work perfectly.
> 
> Thanks anyway,
> Seb
> 
> 
> anthony wrote:
> > This happens to me when the wire is about ready to
> break. The lead 
> > wire is maybe only one filament or two of actual
> copper wire - ergo it 
> > has a higher resistance.
> >
> > ----- Original Message ----- From: "Seb Francis"
> <seb at burnit.co.uk>
> > To: "Synth DIY" <synth-diy at dropmix.xs4all.nl>
> > Sent: Wednesday, March 29, 2006 4:17 PM
> > Subject: Re: [sdiy] DMM problems [OT]
> >
> >
> >> Seb Francis wrote:
> >>> It reads about 500R in autoranging mode and
> different readings in 
> >>> each range when manually ranged (from about 30R
> up to 20M depending 
> >>> on range).
> >>>
> >> Sorry, should have said "with the inputs
> shorted".  When measuring a 
> >> resistor the reading is similarly way off (much
> higher than it should 
> >> be)
> >>
> >> Seb
> >>
> >>
> >>
> >>
> >
> >
> >
> >
> 
>