WTB Toneohm or Milliohm meter - Page 1
Forum section: electronics / general

author: deephaven
author_rank: Frequent Contributor
timestamp: June 26, 2015, 01:33:51 pm
content: Some time back a completely blew up my beloved Toneohm. I miss it and need a replacement. Any ideas on where I can get one or some other milliohmeter from? Preferably in the UK.

author: Zucca
author_rank: Unknown
timestamp: June 26, 2015, 01:50:21 pm
content: Do you feel lucky today?eBay auction: #131543875177Why not get a 6.5 Digit bench DMM?

author: deephaven
author_rank: Frequent Contributor
timestamp: June 26, 2015, 01:54:02 pm
content: Quote from: zucca on June 26, 2015, 01:50:21 pmThanks. I did see that but the postage is a bit steep to get it from the US to the UK.

author: Zucca
author_rank: Unknown
timestamp: June 26, 2015, 01:59:05 pm
content: got it,You could try to ship it first to US....https://www.eevblog.com/forum/buysellwanted/favour-needed-from-somebody-with-a-us-shipping-address/

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2015, 02:35:16 pm
content: @DeephavenI own several Toneohm units, all in good condition.I will see what I can dig out of the cupboards. For a reasonable price I will part with one. I believe I have the 550 model that I am willing to sell. The 850 is my main unit on the bench and I have a 700 for portable work.PM me with the sort of money that you are willing to pay for a good condition 550. We can then discuss further when you have seen pictures of the unit.A similar 550 unit is shown here:http://www.pcbequipment.com/quicksearch/ToneohmI am located in Milton Keynes. UK.Aurora

author: Zucca
author_rank: Unknown
timestamp: June 26, 2015, 02:47:39 pm
content: Just curious, is it so useful to have a tone pitch related to the R measured? I have never had the pleasure to deal with such a puppy.Although just the idea to hear BIP BOP BIIIIP BOOOP all the time is driving me nuts...

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2015, 03:07:59 pm
content: It is first and foremost a milliohm meter for PCB track resistance measurement. It has an LCD display and a tone generator with variable volume so can can turn that off. The tone that it produces can be of help when working on a PCB with shorted Tantalum decoupling caps or whatever. As you get closer to the source of the problem you can hear the pitch change. If you take a wrong turn you can quickly hear it and revert to the last position and retry.You may be surprised at how quickly a Toneohm will track down power rail shorts to a specific component. It is sometimes easier and quicker to listen than to place probes and look up at the display. I personally find that the tone is not annoying as you are concentrating on it as it literally leads you by the nose to the source of the problemIt does take some practice, but once you master a Toneohm you will not want to be without one...... especially if working on Racal equipment that is filled with old tantalum power rail decoupling caps !I have also found faulty chips that have gone low ohms to the 0V rail. Far quicker than cutting tracks and lifting components to identify the exact location of the issue. You can use the Toneohm to trace non power supply rail faults but you really need a schematic so the you can see where you are going with it.My higher end units also have a current/signal tracing capability using a low impedance tone injector and inductive directional probe.These units have been around for a lot of years. The earliest units were just a variable tone audio continuity meter. Then an analogue meter was added, followed by a digital meter for more accuracy.The latest units can track down a power plane fault on a multi layer PCB using a sort of triangulation system guiding the operators probe to the source of the problem !Aurora

author: Zucca
author_rank: Unknown
timestamp: June 26, 2015, 03:27:46 pm
content: Thx Aurora, your posts are always so useful.I think I can do a script in Matlab reading the R from a DMM via GPIB or whatever and then generate a sound from the PC.... just to test it out.Oh well my to do list is keep growing and growing... like my belly.PS: I could assing a musical note instead of a sine tone, let´s dance the Harlem shake repair...

author: PlainName
author_rank: Super Contributor
timestamp: June 26, 2015, 03:46:06 pm
content: For short tracing, wouldn't a HP 547a current tracer, coupled with a 546a logic pulser, be suitable? And cheaper, plus easier to find/repair

author: kripton2035
author_rank: Super Contributor
timestamp: June 26, 2015, 04:05:39 pm
content: @Aurora,what is the resolution (practical) of the 550,700 or 850 toneohms ? is it the milliohm or lower ?thanks.

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2015, 04:38:23 pm
content: Manual is here and contains specs.http://exodus.poly.edu/~kurt/manuals/manuals/Other/POLAR%20INSTRUMENTS%20Toneohm%20550%20Operation.pdfhttp://exodus.poly.edu/~kurt/manuals/manuals/Other/POLAR%20INSTRUMENTS%20Toneohm%20550A%20Operator.pdfThe 550 has a 200 MilliOhm fsd range on a 3.5 digit LCD Display.The p.d. at the probes is only 60mV so no false trails caused by biased semiconductors.All I can say from the practical point of view is that the Toneohms have worked for me and others in tracing down to a faulty component lead. It is definitely a Mlliohm instrument.Aurora

author: kripton2035
author_rank: Super Contributor
timestamp: June 26, 2015, 08:55:27 pm
content: I've build this milliohm meter :http://kripton2035.free.fr/Continuity%20Meters/continuity-an220.htmland it works quite nicely. the last digit is stable, althought it's build on a veroboard !I'm modifying it to add a tone depending on the ohm value, and also a higher range up to 100 ohmsso I would like to know what is the audio frequency output when you have zero ohm, and 100milliohm, 500milli , or 1 ohm ?can you measure it on your polar instrument ?

author: Fraser
author_rank: Super Contributor
timestamp: June 26, 2015, 09:33:29 pm
content: @kripton2035,I am not working in the lab at the moment as other priorities are keeping me busy. I will check audio frequencies when able. I do have the schematics of the Toneohm units somewhere if you want it.Aurora

author: Shock
author_rank: Super Contributor
timestamp: June 27, 2015, 02:20:37 am
content: I would get this micro ohm meter it's cheaper, new comes with kelvin leads and has far better single digit resolution as well so it means it's useful for contact resistance (e.g. testing connectors and switches).www.ebay.com/itm/111378757065I would buy one, but I have good resolution on my LCR meter so am not in a hurry. If you have milliohms or better resolution on an LCR meter (with low test voltage) you could do the same.The main problem with this one is it does not mention the exact working test voltage (just 0-3.5V) so hard to tell if it will switch on junctions or not. I would be interested to see this captured in operation on a scope.I've been looking around if these were based on a project as I'm keen to make one myself and maybe change the design a little. So if you buy one and open it up, let me know.

author: _Wim_
author_rank: Super Contributor
timestamp: June 27, 2015, 06:32:26 am
content: I bought this to use together with my brymen bm869:http://jaanus.tech-thing.org/category/half-ohm/Works excellent! (no affiliation with the seller, just a happy customer)

author: deephaven
author_rank: Frequent Contributor
timestamp: June 27, 2015, 09:00:25 am
content: Quote from: _Wim_ on June 27, 2015, 06:32:26 amThanks for the suggestion, it looks like a nice unit.I prefer something with a variable frequency audio tone for homing in on those PCB shorts.