Hi, John.. I have one of the Tone Ohm units, but I'm not sure where it is at
the moment.
I agree, that milliohm meters are very useful in finding circuit faults (on
bare or populated boards), and some ESR meters may also be useful if the
circuitry isn't massively large.
I've recommended milliohm testers in SER over the years, although I'm not
sure that I included any details wrt the probes.
There are likely SER archived posts which may include ToneOhm milliohm meter
or Polar Instruments comments.
The obvious advantage to a real milliohm meter is the digital display,
although they also incorporate an audio tone which changes with differences
in readings/actual circuit board resistance changes.
The probe for the Tone Ohm model I have (white case with red panel
silkscreening), IIRC, is a fairly common 4-pin connector used for
transceivers (CB, amateur radio etc) with 2 sections of small, flexible coax
(one for each probe), where the 2 conductors of each probe make a 4-wire
bridge-type input circuit.
The 2 probes themselves aren't anything special, just ordinary probes with
sharp steel tips.
There is a Cal pot and built-in test point on the back panel of the ToneOhm
unit I have, so there is some wiggle room for what materials might be
suitable for the brobes and cables.
I got some Fluke probes with sharp steel points for my Blue Bob Parker
Anatek ESR meter, and they're working fine.
FWIW, some instruments as you probably already know, are more critical of
Zero-Set settings, and I've found that steel points break thru any surface
oxides on a test piece (a coin, single solder pad or other metallic surface)
and sharp steel points appear to be less problematic IME.
I generally don't rely on touching probe tips together for Zero-Set,
although not an issue with Bob Parker's tester, but some instruments are
more fiddly.. so I like to pierce any surface contamination and use an
actual reading for zero.
After I bought the used Tone Ohm a number of years ago, a friend bought a
similar unit by Polar Instruments (older model 900 maybe, marketed by a US
company) without a probe, and I made a probe set for him from two sections
of thin coax (maybe RG 174) and it worked correctly.. I vaguely recall that
the probes for the Polar model utilized two sections of coax per probe using
the shields as separate ground connections.. definite maybe, I guess.
--
Cheers,
WB
..............
"John Robertson" wrote in message
...
Or you could track down a Shortsqueek by Global Specialties Model
SQ-1.Made in the 1970s and 80s it is a handy device to keep to track down
shorts on PCBs. Using a small op-amp that changes pitch depending on how
low the resistance is you can find shorts such as you describe fairly
quickly as long as your ear is good for tone changes of a few Hertz. Polar
Devices (UK) made Tone Ohm which was a similar device (I need a probe if
anyone has a spare) that I haven't been able to test (because I'm missing
the probe!).
Here is the manual for Shortsqueek (470k PDF)
http://www.flippers.com/pdfs/GlobalS...Model_SQ-1.pdf
These turn up on eBay from time to time - I bought two for my shop and
they do save hours of time (and chopping traces) every now and then...
John :-#)#
--
(Please post followups or tech enquiries to the newsgroup)
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