Toneohm 850A short finder by Polar Instruments - a look under the hood. - Page 1
Forum section: electronics / testgear

author: Fraser
author_rank: Super Contributor
timestamp: September 04, 2015, 07:27:40 pm
content: For those unaware of the Toneohm units, they are units that contain a Milliohm meter for measuring track resistance and in some models a signal injection and non contact tracing probe.The indicators on the unit are an LCD display and an audio tone that changes with the displayed reading.The purpose of these units is to trace a short circuit caused by a PCB fault or a failed component, such as a power rail decoupling capacitor. In the hands of an experienced operator, these units quickly identify the cause of a low impedance or short, right down to the component or track location.Several models of Toneohm have been made. The original unit had an analogue meter and the tone generator. It was just a Milliohm meter. The later range contained units that were just Milliohm meters or a Milliohm meter plus the signal tracer capability. I highly recommend the latter as the inductive probe quickly leads the user to the cause of the problem. These work superbly on the power rails of Racal equipment that commonly suffers failed power supply decoupling capacitors.Models:500A Original analogue meter + Audio tone Milliohm meter550 Digital display + Audio tone Milliohm meter550A Facelifted 550. No significant improvements to design580 Signal injector and tracer only700 Highly portable Digital Display Milliohm meter + Audio tone + signal injector & tracer probe850 Bench mounted Digital Display Milliohm meter + Audio tone + signal injector & tracer probe850A Facelifted 850 Bench mounted Digital Display Milliohm meter + Audio tone + signal injector & tracer probeThe later 950 model is a very different vector analysis design that is very different to those above and is not covered here.I own the 550, 700, 850 and 850A models. All perform well but those with the signal tracing capability are my favourites. You inject a signal from the unit into the faulty PCB track and the inductive probe picks up the ac signal along the trace until the point of the short is found. The signal stops when you move beyond the faulty component.These units have rocketed in price on ebay in the last year or two. I know not why. I was lucky to buy most of mine prior to the price increase. and all cost me less than £70. You see them listed at over £200 these days.Thanks to fellow forum member Lukier, I became aware of an ebay seller offering a pair of 850A units sans probes for only £50 the pair. I snapped them up as the probes are the same across the models. I have several cable sets and inductive probes to use with themLukier bought the other two units that were on offer. A real bargain if they worked.The units arrived this week and are in far better condition than I was expecting. There is some discolouration of the cases due to UV but this is very common on such cream/grey plastics and is no major issue for me. Both units work fine and perform as they should.I opened the units and stripped them to enable me to clean the cases. I took some pictures of one unit for your interest. The design and PCB layout is very 'old school' but is of high quality and well laid out. As the bench case is large, the various elements of the design are separated into their own section of the PCB. Very neat and orderly.I have the service manual and schematics but sadly the file is too large to include on the forum. Sorry.These units are easy to maintain and spare parts are still available from POLAR Industries. A pair of very sharp tipped Kelvin type probes costs around £40 but you can make your own easily. The inductive probe is also available for around £40. Prices include VAT and delivery.Now to the pictures......

author: Fraser
author_rank: Super Contributor
timestamp: September 04, 2015, 07:28:26 pm
content: Internal pictures of the 850A......Note the convenient voltage test points in the middle of the PCB. It couldn't be easier.Aurora

author: Fraser
author_rank: Super Contributor
timestamp: September 04, 2015, 07:29:56 pm
content: More pictures.......

author: Fraser
author_rank: Super Contributor
timestamp: September 04, 2015, 07:30:28 pm
content: More pictures.......Note the quality parts used....Dubilier Capacitors in the PSU. Still working fine.

author: Stray Electron
author_rank: Super Contributor
timestamp: September 04, 2015, 07:32:45 pm
content: Aurora,Great write up! I've been wondering about these for a long time, particularly the difference in the various models. You've answeredallmost, of my questions. Can you tell us more about the probes? How hard is it to make them if we buy a unit without probes?

author: lukier
author_rank: Unknown
timestamp: September 04, 2015, 07:53:26 pm
content: Thanks Aurora for sharing your knowledge on these and teardown pictures so I don't have toI didn't even have a chance to unpack my 850As yet and I don't have the probes. I will email Polar and ask for a quote.BTW These things are miliohm meters, but is it really usable? I'm thinking about buying 1-10 mOhm Vishay Precision current sense 4 terminal resistor from Farnell to build DIY alternative to Keysight's 34330A (and use it to calibrate power supplies current ranges - Guildline resistors recommended in Keysight's calibration manuals are pure unobtainium).I also have DE-5000 and robrenz did interesting experiments showing that it could be used as a miliohm meter. However, in my case it will be sub 10 mOhm so a meter even with with 1 mOhm resolution (not to mention accuracy) is not going to cut the mustard.I don't have 34420A that would be good for the job, but I have Stanford Research SR850 and I thought I might measure such low resistance by pushing AC sine excitation (that has output resistor/impedance to limit the current) through the current shunt and connecting signal input to sense terminals. SR850 can resolve down to 2nV and has sub 8nV/root Hz noise floor if I remember correctly.Does the route with lock-in amplifier makes sense?

author: Fraser
author_rank: Super Contributor
timestamp: September 04, 2015, 07:55:39 pm
content: @Stray Electron,Making your own probes.....1. The Kelvin probes are easily DIY built. You just need the correct 5 pin DIN plug, some thin coax cable and a pair of decent sharp tipped probes. Each coax is connected to 2 pins in the DIN plug and the coax braid and inner conductor are connected together at the metal probe tip. Not true Kelvin probes but close enough for these units and this is how they are made by POLAR.2. The Signal Injector cable is very simple to DIY. It is just a pair of test clip leads connected to the required pins in the appropriate DIN plug3. Signal tracer probe is not a DIY option until its internal parts are identified and understood. The probe is likely a coil on a ferrite core and it is very directional. I may be able to X Ray my probes to see what can be revealed. I bought new probes from POLAR industries for £40 as I wanted good performance and the time to make the probes would have exceeded the new parts purchase price. If I can reveal more about the probes contents, I shall post it in this thread shortly.The DIN plugs are standard 'off the shelf' items and they do not contain any components.Aurora

author: Fraser
author_rank: Super Contributor
timestamp: September 04, 2015, 08:03:25 pm
content: There is a 550A for sale on ebay UK at the moment. It may go for a bargain price?http://www.ebay.co.uk/itm/181852968902?_trksid=p2060353.m1431.l2649&ssPageName=STRK%3AMEBIDX%3AITAurora

author: Fraser
author_rank: Super Contributor
timestamp: September 04, 2015, 08:36:33 pm
content: @Lukier,My two units cleaned up really well and work perfectly. We have two different versions of the 850A. One has the Grille on the front and was made on 1996. The other has the speaker grille underneath and a plain front and was made in 1999.The Toneohm 850A uses a common ICL 7106 3.5 digit LCD voltmeter chip. IIRC this is not a super accurate device.I would not trust it as a Milliohm meter. It can measure very low resistances and provide a reading useful for finding shorts, but it is not designed to be a Milliohm meter so will not have the resolution or accuracy that your are looking for.I regret I am not able to help on your question further as measuring low resistances or impedances is not something I have been involved with over the years.Aurora

author: lukier
author_rank: Unknown
timestamp: September 04, 2015, 08:43:34 pm
content: Quote from: Aurora on September 04, 2015, 08:36:33 pmI've noticed the grille difference on eBay photos and got intrigued. Thanks for solving this mysteryQuote from: Aurora on September 04, 2015, 08:36:33 pmI suspected so.Quote from: Aurora on September 04, 2015, 08:36:33 pmNo worries. Maybe someone else on the forum will enlighten me if a lock in amplifier makes sense for microohm measurements

author: kony
author_rank: Regular Contributor
timestamp: September 04, 2015, 09:13:59 pm
content: Quote from: lukier on September 04, 2015, 08:43:34 pmSure it does.

author: lukier
author_rank: Unknown
timestamp: September 04, 2015, 09:32:32 pm
content: Thanks for confirmation!I found this article by Keithley on AC vs DC for sensitive measurements:http://www.keithley.com/data?asset=50671and they (of course) suggest their nanovoltmeters, but now I think lock-in amp will do fine for my purpose.

author: Fraser
author_rank: Super Contributor
timestamp: September 04, 2015, 10:08:37 pm
content: I was feeling in a helpful mood so have taken some pictures of my complete 850 and probes set.I got it wrong on the inductive probe in that it has a 1 Ohm resistor in its DIN plug. I attach a quick sketch and images.The inductor in the inductive probe measures 9.6 Ohms but I will have to measure its inductance tomorrow as I am not in the lab.I have also X-Rayed the probes and attach them in later posts for your interest and information. The component at the tip of the inductive signal tracer probe appears to be a simple tiny ferrite bobbin inductor. This should be simple to copy once I have the inductance value. The Injected signal is not a very high frequency so COTS bobbin inductors should be available.Aurora

author: Fraser
author_rank: Super Contributor
timestamp: September 04, 2015, 10:10:28 pm
content: X-Ray images of the Inductive probeThey are quick and dirty so apologies about the quality !

author: Fraser
author_rank: Super Contributor
timestamp: September 04, 2015, 10:12:41 pm
content: X-Ray of the connections to the contact probe tips. As you can see the inner conductor and coaxial braid are connected together at the metal tip solder bucket.

author: lukier
author_rank: Unknown
timestamp: September 04, 2015, 10:48:57 pm
content: These Faxitron x-ray images are a thing of beauty.It really looks like a COTS SMD inductor.

author: Fraser
author_rank: Super Contributor
timestamp: September 04, 2015, 11:06:18 pm
content: LukierI agree. I imaged it at two angles and it certainly looks like an SMD bobbin inductor with a base to which the wires are attached.The images that I produced this evening are very rough and far from what is achievable with the MX-20. I started it from cold, did a quick calibration and did not even give the sensor array time to warm up properly. Good enough for our present needs though. The MX-20 has a lot of image manipulation and enhancement menu options that can really tidy up an image and improve clarity where needed. Sadly it is limited in terms of penetration though as it tops out at 35KVp. This is why I cannot penetrate through the inductor core. At least not at 30KVp with a relatively short 5 second exposure. I could try a longer exposure and 35KVp but time was short this evening.The MX-20 can also measure the bobbin for us if we need dimensions as it is able to calculate dimensions even when using the upper (magnification) shelves in the cabinet. I will supply the inductance value as soon as I can get in the lab. Other tasks to do first though. I can also take some close up pictures of the probe head if needed by others. It isn't very sophisticated though. Fortunately I found no other components in the handle of the probe so it is just a simple inductive pick-up probe.Aurora

author: lukier
author_rank: Unknown
timestamp: September 06, 2015, 12:46:57 am
content: I just spotted this on eBay:http://www.ebay.co.uk/itm/291555781429This is I believe the most advanced model with some sort of triangulation to find power/ground plane shorts.I'm fine with 850A but I thought this might be of interest to other forum members. With 950 model (still manufactured and with probes) it is likely that bidding will go pretty high.

author: Fraser
author_rank: Super Contributor
timestamp: September 06, 2015, 12:32:17 pm
content: Yes the 950 is the current model and is designed to cope with shorts on power planes. Using triangulation. They always sell for a lot of money and in my opinion, are not that much useful to the hobby user as they really are for production line fault tracing where a PCB power plane has suffered a supply to 0v short due to PCB production fault. Triangulation does not work on conventional PCB's that do not contain a power plain as the stimulation probes need to be positioned at the four corners of the PCB.The 950 is very clever, but very much a production tool rather than general repair. Computer repairs may benefit from the triangulation mode though as the motherboards have a power plain.Aurora

author: nowlan
author_rank: Frequent Contributor
timestamp: September 06, 2015, 12:53:36 pm
content: I saw a repair video once, where the kid had some flash 6.5 digit multimeter, and just dragged the probes along power rail, until he found the shorted capacitor watching the track's ohm decrease.Ive only seen tone generators for tracing wires, like in car stereo, to see where they run behind panels.

author: Fraser
author_rank: Super Contributor
timestamp: September 06, 2015, 03:11:25 pm
content: A tone ohm just uses basic physics in its operation. It's function can be mimicked to a degree by a Milliohm meter. The Toneohm has the added benefit of a varying frequency audio tone and a signal tracer probe. The venerable HP Current probe is also capable of finding shorts.... But it can be an expensive purchase these days.The Toneohm is a classic case of an instrument that contains several elements that make it a very versatile and useful tool on the bench. As can be seen in the pictures though..... There is no rocket science inside the case. It's an oldy but goodyAurora

author: Fraser
author_rank: Super Contributor
timestamp: September 06, 2015, 03:26:45 pm
content: OK I have just measured the inductance of the probe inductor......1KHz ... 220uH Q =0.14510 KHz ... 220uH Q=1.442100KHz ... 225uH Q= 12.68Aurora

author: lukier
author_rank: Unknown
timestamp: September 06, 2015, 03:53:30 pm
content: Thanks!With the inductance value and those beautiful Faxitron images I'm really tempted to DIY something (both current and pointy kelvin probes) instead of contacting Polar. 40 quid here, 40 quid there and it adds up. Instead I can buy a bunch of DIN connectors and various SMD inductors from Farnell, sharp probes from eBay/Aliexpress, I have some RG158 coax , current probe handle I can probably 3D print out of ABS and I will still have money left for some other useful gear

author: Shock
author_rank: Super Contributor
timestamp: September 06, 2015, 04:13:23 pm
content: If your interested in current tracers check out the HP 547A. The HP Journal from December 1976 has some real good reading in it as well.

author: Fraser
author_rank: Super Contributor
timestamp: September 06, 2015, 05:01:58 pm
content: @Shock,That is the HP current tracer probe that I haveAn ex MoD new set of HP current probe, logic pulser, logic probe and logic clip cost me £60, but they sell for around £100 these days.Aurora

author: PA4TIM
author_rank: Super Contributor
timestamp: September 07, 2015, 07:28:44 am
content: Those X-rays are really cool. Together with some thermal image cameras a very usable tool for repairing (but a bit out of budget)For the readers who like to build a shortfinderhttp://www.pa4tim.nl/?p=5339(a Bob Pease design and a Bob Smith design)I made two shortfinders but I also have a DE5000 and some 6,5 and 7,5 digit meters. The problem in short-finding is that you need to look at the meter and the pcb at te same time. That is why the tone is helpfull.But when you have a multilayer board a multimeter or other contact-making probe is not handy. An other problem is that some use a rather high current. The inductive pickup like in the Smith model does not have those limitations. The problem with this inductive pickup is that it needs some practice and a careful placement/direction of the probe. But by making serveral probes it can work over a huge current range (I start at 6mA) To overcome the inductive "problems" I made a probe from an old cassette tape player. And that works even better and a lot more easy as the inductive probes. It is very directional.An other way could be to use a Hall sensor probe. I tried this (not as a probe for this tracers) but my sensor is not sensitive enough for this purpose.

author: Shock
author_rank: Super Contributor
timestamp: September 07, 2015, 08:30:01 am
content: Quote from: Aurora on September 06, 2015, 05:01:58 pmI have two, one for each hand.

author: lukier
author_rank: Unknown
timestamp: September 15, 2015, 10:14:34 pm
content: Thanks to Fraser, equipped with all the information he provided here, I decided to go the DIY way and make the probes.For the miliohm probes I bought these cheapies, fairly sharp:http://www.ebay.co.uk/itm/221771743126The cable is pretty much just held by strain relief plastic, so I cut cable there, drilled through the strain relief and by pulling the tip I could get remaining wire out. Then cut remaining cable close to the back side of the tip and I've used RG174, poor-man Kelvin soldered there. Coax diameter roughly matches the original cable. After assembling everything I put a drop of super glue in the strain relief and between needle plastic and handle tube. On the other side I used NYS322 connector from Farnell.Drive probe is just MAS 50 connector from Farnell, fine silicone insulated wires terminated with pin header connectors. This way I will be able to change between small micrograbbers (from logic analyzer), normal hooks and pin headers.Current sense probe was a bit of long shot. NYS322 connector as before, 0603 1 Ohm resistor there inside, RG174 coax and LQH32CN221K23L inductor from Farnell. It is very small (1210) and I checked it with DE5000 and got similar readings to what Fraser measured.I still need to read the manual to make sense of the noise this box makes, but the current sense probe test was I think most intuitive and it seems to work well. Now I need to design & 3D print appropriate case for this inductor.

author: Fraser
author_rank: Super Contributor
timestamp: September 15, 2015, 10:53:42 pm
content: Hi Lukier,Nice workI will replicate it to make probe sets for my two units.Thanks for sharing your workFraser

author: PA4TIM
author_rank: Super Contributor
timestamp: September 16, 2015, 06:44:04 am
content: Nice done. That is funny, I have done almost the same thinghttp://www.pa4tim.nl/?p=4207(but then for use with a multimeter.I also used RG179 but in my case for a pair of Kelvin clips.However, for the multimeter style probes I used a pair of old probes from Hirschmann if I remember well. You can scew the points out. I soldered the (lemo multistrand) wire as close to the tips as possible. This works very well. For the "mechanically challenged" person that could be an alternative option.This kinda semi kelvin probes work fine for most cases and are often much more easy to use as kelvin clips.Robertz has a video about making real multimeter style kelvin probes. I am rather handy in mechanical things and I can make a lot of things but after watching Robertz making his probes I feel like I'm a mechanical retard

author: lukier
author_rank: Unknown
timestamp: September 16, 2015, 10:27:25 am
content: Quote from: PA4TIM on September 16, 2015, 06:44:04 amThanks. In my case I wanted to replicate the original Polar probes as close as possible and continue being cheapskate at the same timeNice write up. I like the splitter box in particular. I want to build something similar for my DE-5000. I have crocodile clips and tweezers adapters, but I also want proper kelvin clips so recently I've ordered these cheap BNC to Kelvin Clips from China and I want to 3D print some kind of adapter from DE-5000 to 4 BNCs (as seen on benchtop HP LCR meters).Quote from: PA4TIM on September 16, 2015, 06:44:04 amMe tooI pretty much just have Proxxon Micromot kit, few hand tools and CNC 3020T that is still "work in progress" (working on my own controller) so every time I read Robrenz posts I'm amazed at the spectrum of the tools he has at hand. And then I've read his post on restoring Tek plugins and there he uses old school font engraving pantograph - mind blown

author: Fraser
author_rank: Super Contributor
timestamp: September 16, 2015, 10:29:45 am
content: With regard to inductive probe casings,..... In the past I have needed nicely shaped probe handles so took a look at the pens sold in the supermarket. There are some very nice looking pens that can be adapted into prone handles. I am not talking about cheap BIC pens, but nicer offerings from the likes of Papermate etc. Some are even shaped to fit comfortably in the hand.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: September 16, 2015, 08:30:48 pm
content: Lukier,I just measured the dimensions of the inductive probe tip and I must say your choice of Murata SMD inductor looks spot on.The tip measures 3.3mm x 3.7mm at the point where the inductor is located.Those dimensions match the Murata inductor well. The original probe appears to have had the probe tip moulded In resin around the inductor. I will likely place the inductor inside a thin wall ABS tube used in modelling. Such is perfect for the task and may be filled with glue or silicone before being mounted in a pen shell.Fraser

author: lukier
author_rank: Unknown
timestamp: September 16, 2015, 10:02:17 pm
content: Thanks!Now the only problem is that I bought the last 3 inductors from FarnellEven had 2 on back order (it was min qty 5).The replacement they are suggesting looks like a shielded inductor (full ferrite), not very similar to what I deducted from your x-ray photos. I don't know if this matters much.On the website they suggest alternative and there is some lead time date, however I got an email from them saying:Code:Thank you for placing an order with us recently. Unfortunately, we are unableto supply you with the item(s) listed below, and have had to delete them fromyour order(s). Where there is a suitable Alternative we have listed this below.Please accept our apologies for any inconvenience this may cause. If this doesnot affect you directly, please forward to the user of this product(s).Original ProductProduct Notification Reason NO LONGER STOCKEDFarnell Order Code 9522239Product Description INDUCTOR, 1210 CASE, 220UHManufacturer/Brand Name MURATAManufacturer Part No. LQH32CN221K23LPurchase Order Number 14/09/15 14.16Date Ordered 14/09/2015Qty Outstanding 2There is no suitable alternative for this product.I think Mouser still has them.

author: Fraser
author_rank: Super Contributor
timestamp: September 17, 2015, 10:57:32 am
content: Thanks, I saw that Farnell no longer have stockI ordered 5 from an eBay seller but I am expecting him to refund as he likely just buys Farnell parts and on forwards them. There is a Murata 1208 part that may be available. I will check. If all else fails, I can find something similar that is nor screened. I don't see a major issue with using a slightly different inductor value either. This is a non resonant, non critical role for the inductor.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: September 17, 2015, 07:59:59 pm
content: Interesting development..... The eBay seller of the Murata SMD inductor had despatched 5 to me today.Either he has a different supplier or was holding stock.I just ordered another 10.Seller is Petelox. I have bought from him before and he has been reliableFraser

author: Fraser
author_rank: Super Contributor
timestamp: September 20, 2015, 08:24:53 pm
content: The inductors arrived from Peter Lox. They are the correct bobbin size and spec but have come from Radio Spares. I now have some to experiment with.Fraser

author: caius
author_rank: Regular Contributor
timestamp: May 21, 2016, 02:40:45 pm
content: Sorry for bumping this thread.I bought a Polar Toneohm 850 , I still have to receive it but it will come witouth any probes so I'll probably build them myself rather than buying the original ones from Polar.Is there any pinout of the various connectors in order to know which are the pins to use on the cables?Thanks.

author: lukier
author_rank: Unknown
timestamp: May 21, 2016, 03:29:48 pm
content: Quote from: caius on May 21, 2016, 02:40:45 pmCheck Fraser's post for photos of the plugs and pinouts:https://www.eevblog.com/forum/testgear/toneohm-850a-short-finder-by-polar-instruments-a-look-under-the-hood/msg747123/#msg747123and my post for part numbers:https://www.eevblog.com/forum/testgear/toneohm-850a-short-finder-by-polar-instruments-a-look-under-the-hood/msg755627/#msg755627also service manual / schematic. Both probe connectors can accept either Kelvin or Current Tracer probe, only Drive Source is a separate one.

author: caius
author_rank: Regular Contributor
timestamp: May 21, 2016, 05:45:15 pm
content: OK, thanks, I got it.Looking at schematics of Toneohm 850A (whose PCB should br the same of 850) I figured out pinout for building my cables.I guess the black clip of the drive source must be connected to the pin of J3 which goes to the inverting input of the LM339 OP-AMP while the red one to the pin that goes to the not-inverting input.Obviously this matters when you track the voltage injecting direct current to the circuit and not when you use the non-contact current tracing and the inductive probe since you are injecting alternate current.I attach part of schematics for the three connector J1-J2-J3.

author: mmagin
author_rank: Frequent Contributor
timestamp: May 21, 2016, 11:19:18 pm
content: Quote from: Fraser on September 04, 2015, 07:55:39 pmOoh! This sounds very similar to that 1970s hp current tracing probe that was introduced along with the pulser and logic probe. (Which goes for too much on eBay)

author: caius
author_rank: Regular Contributor
timestamp: May 27, 2016, 03:15:37 pm
content: I received my Polar Toneohm 850, sadly the case came damaged and cracked.Anyway the PCB is intact.I'm struggling to find the correct voltage jumper setting for my country (I'm in Europe so 220V), now the unit is set to 120V.I removed the two 120V jumpers (B----D and A----C) and close the 240V one (B----C) but unit doesn't power up at all.I can't find the service manual of model 850 but only the one of 850A which has different PCB.

author: caius
author_rank: Regular Contributor
timestamp: May 27, 2016, 05:58:11 pm
content: OK, the unit is faulty (good bargain..), I don't know if this depends from the damage occured during shipping but it seems strange.PCB inside is intact, no sign of cracks.From my first check I could ascertain that no voltages come out from main transformer 'T1' both in 120V and 220V line selected.Are schematcis available for this model? 850A ones are different and 'T1' transformer changes accordingly the serial number.

author: Fraser
author_rank: Super Contributor
timestamp: May 27, 2016, 06:19:39 pm
content: The 850 has a combination of metal and fibreglass (?) case. Sorry to hear yours got smashed. It should be possible to repair the resin though. Then tidy up with a respray with car paint.Please PM me your email address and I will see if I can supply the 850 service manual. I think I have it in my archives 🙂Fraser

author: Fraser
author_rank: Super Contributor
timestamp: May 27, 2016, 06:39:09 pm
content: Yep, I have the standard 850 (non A) service manual and schematics.I will send once I have your emailFraser

author: caius
author_rank: Regular Contributor
timestamp: May 27, 2016, 06:42:17 pm
content: Quote from: Fraser on May 27, 2016, 06:19:39 pmHi and thanks for replying.I already put pieces together with a superglue, damage (pictures attached) was not wide.But this has few importance, the main problem is that the unit doesn't power on while seller told me it did and sent me also a picture of the display ON.I can measure only 1VAC on the two secondary of the main 'T1' transformer, I think this is the culprit.One of the output goes, after being rectified by a bridge, to the 7805 regulator whch has on his input only 0.5VDC obvioulsy, that's clearly too few for regulationTherefore all the logic inside is not powered.

author: caius
author_rank: Regular Contributor
timestamp: May 27, 2016, 06:46:31 pm
content: Quote from: Fraser on May 27, 2016, 06:39:09 pmI PMed you my e-mail.Thanks again for the help.

author: Fraser
author_rank: Super Contributor
timestamp: May 27, 2016, 07:10:22 pm
content: Caius,I cannot remember whether the transformer is PCB mounted. If so, it is not uncommon for the weight of the transformer to snap a winding connection where it attaches to the PCB pin. I have repaired such failures with a bridging wire between the pin and remaining end of the wire. The primary winding is the most fragile and so most likely to snap.Thankfully the transformer is not too unusual if it has to be replaced. It has three secondary windings that feed three 5V regulators. You might need two replacement transformers to get the three isolated windings though. I suspect a 9V-0-9V and a 0-9V would be a good match.Fraser

author: Shock
author_rank: Super Contributor
timestamp: May 27, 2016, 07:12:36 pm
content: QuoteDid you read that on their website, what a joke.

author: Fraser
author_rank: Super Contributor
timestamp: May 27, 2016, 07:15:45 pm
content: Caius,I have sent you the 850 user manual as well.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: May 27, 2016, 07:19:05 pm
content: Shock,Phew !, I should have asked for £100 for the SMThe Wayback machine is your friend though as all the manuals used to be downloadable for free on the Polar website. I spent a lot of time searching for them and eventually navigated to the right download page.Fraser

author: caius
author_rank: Regular Contributor
timestamp: May 27, 2016, 07:22:09 pm
content: Quote from: Fraser on May 27, 2016, 07:15:45 pmFraser, this is very kind from you, I was going to ask the operator manual as well but you read in my mindWithin some minutes I will post a picture of PCB, I really think the main transformer gone bad due the hit which cracked the case.Anyway I already found another 850 (and 700) from a seller in my country.I think I will take it to do some comparison, I want to repair also the defective one.The only good thing is that seller included both needle and current probes so I have only to build the DRIVE SOURCE leads.Thanks again.

author: caius
author_rank: Regular Contributor
timestamp: May 27, 2016, 07:23:45 pm
content: Quote from: Shock on May 27, 2016, 07:12:36 pmYeah, I have read it.it's ridiculous!

author: Shock
author_rank: Super Contributor
timestamp: May 27, 2016, 07:51:11 pm
content: I've wondered if one of these would ever be useful to me, what do you think Fraser?I have a microohm meter, a few milliohm meters, a current tracer, a picoammeter, logic pulser and probe, several multimeters to do voltage drop/diode tests and my best multimeter isn't amazing but it does DC to about 0.01mV accuracy.Haven't made a decent set of RF probes but I'll probably get around to doing something better than my current hacked together one.

author: Fraser
author_rank: Super Contributor
timestamp: May 27, 2016, 08:15:15 pm
content: The Toneohm makes it easy to track down shorts to ground or across a pair of traces. It leads you by the nose to the cause of the short. the variable tone makes the tracing possible without looking at a display. The inductive probe picks up the emissions from the shorted pcb track that is being stimulated by a low impedance signal generator. it is very effective.If you download the 850A user manual, its capabilities are well documented.I did a lot of repairs on RACAL equipment that suffers failures of the Tantalum supply rail decoupling capacitors. The Toneohm made short work of tracking down the failed capacitors.I like the Toneohm units, and own several models, but it is a bit of a luxury like mt Huntron Tracker units.Fraser

author: caius
author_rank: Regular Contributor
timestamp: May 27, 2016, 08:16:38 pm
content: Fraser, what about the model 700?I have found one at good price.

author: Fraser
author_rank: Super Contributor
timestamp: May 27, 2016, 08:22:49 pm
content: The Toneohm 700 is an excellent portable version of the 850. I own one of those as wellI have the user and service manuals for that model.Fraser

author: caius
author_rank: Regular Contributor
timestamp: May 27, 2016, 08:27:42 pm
content: Oh, my god, but you collect them all!Anyway the one I found has the probes directly soldered inside the unit, I think they didn't find original probe so they chose this 'rude' option.

author: lukier
author_rank: Unknown
timestamp: May 27, 2016, 08:51:56 pm
content: As Fraser and I bought our 850A in sets of two (that's how the guy on eBay was selling) I still have my second one that I don't need. If you are in the UK/EU (so shipping is sensible) I bet we can negotiate mutually agreeable priceThe unit is perfectly fine except yellowish case with some stickers (retr0bright could help but I wouldn't bother to whiten the entire case).

author: caius
author_rank: Regular Contributor
timestamp: May 27, 2016, 09:18:15 pm
content: Quote from: Fraser on May 27, 2016, 07:10:22 pmYou were right, two of three secondary winding are broken near the pin, I attach picture.I'm going to resolder them.Stay tuned.

author: Fraser
author_rank: Super Contributor
timestamp: May 27, 2016, 09:29:35 pm
content: Caius,Yes, I have a collectors mentality to test equipment. I shall be downsizing soonI own the following models of Toneohm550 Qty 2580 Qty 2700 Qty 1850 Qty 1850A Qty 2I attach some pictures grabbed from the internet to show what they look like.Fraser

author: caius
author_rank: Regular Contributor
timestamp: May 27, 2016, 10:47:49 pm
content: I colect me too equipment.I have a Fkule 9010A troubleshooter and various PODs.I have also a BK560 and BK560A IC tester from BK Precision.Some update about my repair.I desoldered the main transfomer and found that also the primary windings (as you suspected) were broken.I rebuilt them with a bit of AWG30 wire.Now it should be OK, tomorrow I will solder it on PCB and test the unit.The two primary windings show a resistance of 570 Ohm and 500 Ohm, this is normal, I presume.

author: caius
author_rank: Regular Contributor
timestamp: May 28, 2016, 07:40:09 am
content: Now it's up and running.The culprit was the main transformer, most of the windings were interrupted.Many thanks to all for help!

author: Shock
author_rank: Super Contributor
timestamp: May 28, 2016, 04:04:47 pm
content: Reading of -4.2 milliohms, the short must be inside the Toneohm

author: caius
author_rank: Regular Contributor
timestamp: May 28, 2016, 06:09:58 pm
content: I made this small video shorting intentionally a 100nF by-pass capacitor on a scrap arcade pcb.@Fraser :Is it normal that speaker will sound in that way when I find the short?Besides, are negative readings on display within the normal range?Is calibration needed?Thanks again for your great help!

author: perdrix
author_rank: Frequent Contributor
timestamp: February 02, 2018, 10:25:30 am
content: Hi all,I just attempted to make a current probe using one of those Murata LQH32CN221K23L inductors which I epoxied into the sharp end of an old ball-point pen.It sort of works but isn't sensitive enough - the best signal I can get out of it performing the following calibration steps in the rather tatty user manual:QuoteThis gives me at best a signal of about 20mV pp that roughly resembles a sine wave.Any suggestions?ThanksDave

author: perdrix
author_rank: Frequent Contributor
timestamp: February 02, 2018, 10:27:17 am
content: Quote from: perdrix on February 02, 2018, 10:25:30 am

author: Fraser
author_rank: Super Contributor
timestamp: February 02, 2018, 12:43:12 pm
content: You did have the signal injector 'loop' shorted when doing the test didn't you ? The RF signal injector only generates its full output when feeding into a low impedance. If you use the inductive tracer probe on the unterminated signal injector probes you will detect very little signal.Fraser

author: perdrix
author_rank: Frequent Contributor
timestamp: February 02, 2018, 03:10:12 pm
content: I had them connected across a 10 ohm resistor as instructed to by the manual.I since then rebuilt this with a new inductor without the housing to determine if the epoxy resin was causing a problem.I still see the same low signal (about 20mV) across C9 (which is directly connected to pins 1 and 3 of the DIN).The Drive Source signal is about 500mVppinto an open circuit and 360mVppacross a 10 ohm resistor.Dave

author: Fraser
author_rank: Super Contributor
timestamp: February 02, 2018, 05:42:06 pm
content: Do you still need the Model 700 manuals, or have you now got them ?Fraser

author: perdrix
author_rank: Frequent Contributor
timestamp: February 02, 2018, 09:07:59 pm
content: I have a pretty scrappy scan of the user and service manuals but would appreciate having better ones.ThanksDave

author: Fraser
author_rank: Super Contributor
timestamp: February 02, 2018, 09:17:15 pm
content: I have the document archive PC back up and running so will send you what I have.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 02, 2018, 10:33:46 pm
content: I have just uploaded the Toneohm 700 User Manual, Service Manual and Application manual to Filedropper........http://www.filedropper.com/toneohmThese are the officially supplied PDF's from Polar when they use to offer such on their web site.EnjoyFraser

author: perdrix
author_rank: Frequent Contributor
timestamp: February 03, 2018, 02:07:39 am
content: Thank youDave

author: perdrix
author_rank: Frequent Contributor
timestamp: February 03, 2018, 11:43:30 am
content: Just to add additional information - the current probe is supposed to be able to work with 200 ohms between the drive source leads.My home made one just doesn't work in this case and the output signal with 10 ohms is 10% of what it is supposed to be, so any ideas to imprive the sensitivity are most welcome.Dave

author: Fraser
author_rank: Super Contributor
timestamp: February 03, 2018, 02:08:37 pm
content: OK, maybe something helpful from me.I tested a 700 before selling it to a fellow forum member. I recall that the 850A probe with its narrow tip produced quite insensitive performance on the 700 unit. I then attached the probe that came with a Polar non contact short circuit tracer (audio only). That probe produced normal performance on the 700. The better performing probe was notable in that it had a much larger tip dimension. Probably around 3X wider than my 850A probe.I am thinking that the 850A and 700 use different inductors in the probe head. I do not have a probe to test at the moment so cannot provide you with the better performing probes inductance. You may have to experiment a little. If you are getting 1/10 the voltage level, try an inductor with 10x the winding count. i.e 10x the value. Be careful what coax you use with the probe. The original coax was just simple low cost audio cable.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 03, 2018, 02:11:34 pm
content: I will upload the 850A schematics as they may show the difference in the probe input circuits.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 03, 2018, 02:17:48 pm
content: I have found possible confirmation of my suspicions regarding different inductors in the 850A Vs the 700 probes. Take a look at the attached pictures. One is of the Polar 580 audio only tracer. I used the probe from one of these for the 700 unit.Then look at the two probe pictures. The fine tip probe is from an 850A. The probe with the wider tip is the standard probe supplied with the 700 unit.Try a larger value inductor !Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 03, 2018, 02:20:51 pm
content: I do have another Toneohm 580 stored away somewhere. If you can wait a day or so, I will find it and measure the probe inductance for you.Fraser

author: perdrix
author_rank: Frequent Contributor
timestamp: February 03, 2018, 04:12:15 pm
content: Thank you very much,Certainly aiming to increase to the turn count by an order of magnitude makes excellent sense, I'll await your measurements on the earlier probe with great interest.I'll await your measurements with great interest.CheersDave

author: perdrix
author_rank: Frequent Contributor
timestamp: February 08, 2018, 11:03:49 am
content: I asked Polar Instruments the price of the current probe for the 700.QuoteOuch!Dave

author: Fraser
author_rank: Super Contributor
timestamp: February 08, 2018, 01:52:21 pm
content: Yes, sadly they are expensive. I purchased one when they were less than £50 +Vat but that still hurt !I will try to find the other 550 for testing today.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 14, 2018, 10:12:14 pm
content: OK, I have, at last, managed to dig out the Polar 580 and it's probe.I desoldered the probe coax cable from the PCB and took the following measurements using my Mastech MS5308 and DER EE DE5000.Mastech MS5308F = 1KHz L = 986.4uH Q = 0.218F = 10KHz L = 986.5uH Q = 2.14F = 100KHz L = 1100.1 Q = 14.09DER EE DE5000F = 1KHz L = 981.4uH Q = 0.217F = 10KHz L = 982.6uH Q = 2.14F = 100KHz L = 1100.9uH Q = 14.73The Resistance is measured at 28.3 Ohms including the coaxial cable of approx 0.5m.The physical measurements of the probe tip are : 5mm x 4mm x 10mm long.A SMT inductor of spec 1mH @ 100KHz and Rs 28 Ohms looks appropriate.Hope this is of assistance to those who wish to make their own probe for Toneohm units that require this larger inductance in the probe head.Fraser

author: perdrix
author_rank: Frequent Contributor
timestamp: February 16, 2018, 06:17:50 pm
content: I bought some Murata LQH43MN102J03L 1mH (size 1812) inductors.I'm delighted to report they workperfectlyfor making your own ToneOhm 700 current probe.When I do the calibration setup I get about 150mVppas the best signal when adjusting R78 with the drive source connected across a 10 ohm resistor.So that's another "little" job finished.Thanks to Fraser for measuring his probe.CheersDave

author: Fraser
author_rank: Super Contributor
timestamp: February 16, 2018, 06:47:08 pm
content: Thank you for highlighting this difference between models of ToneohmFraser

author: perdrix
author_rank: Frequent Contributor
timestamp: February 18, 2018, 01:10:01 pm
content: Just for the halibut, here's a picture of the completed probe made from a ballpoint pen that I repurposed ...CheersDave Partridge

author: Fraser
author_rank: Super Contributor
timestamp: February 18, 2018, 01:41:44 pm
content: Nice workFraser

author: aqibi2000
author_rank: Regular Contributor
timestamp: December 12, 2019, 11:16:57 am
content: Hi Fraser,You don’t also happen to have a Polar t2500/3000/4000/6000 with a small CRT display?My screen is very dim and looking for a comparison to help fix it the issue.Cheers

author: fcb
author_rank: Super Contributor
timestamp: December 12, 2019, 12:29:23 pm
content: Reach out to Polar Instruments - they are good guys and might help you with schematics of old products.I have a mint 950 ToneOhm and all the toys, rarely used sadly - still current model I believe.

author: Fraser
author_rank: Super Contributor
timestamp: December 12, 2019, 01:31:43 pm
content: +1 on contacting Polar. They certainly helped me when I needed support for one of their older units.Fraser

author: aqibi2000
author_rank: Regular Contributor
timestamp: December 15, 2019, 11:12:10 pm
content: Great to hear that, can either of you suggest a contact since I have not heard back from : neil@polarinstruments.com since my email last Monday.You should look into the V/I tracers fantastic for faulty funding too.

author: Fraser
author_rank: Super Contributor
timestamp: December 16, 2019, 12:05:38 am
content: I have several Polar and Huntron V/I tracers in the labAs you say, very usefulFraser

author: all_repair
author_rank: Frequent Contributor
timestamp: December 16, 2019, 02:32:38 am
content: Likely I am doing wrong, I am not able to apply consistent pressure on the measuring points. My objective was to use it to find the shorted component (location). The differences in the applied-pressure appears to be more than the trace resistances so I find the tracer impossible to use. Help me.

author: aqibi2000
author_rank: Regular Contributor
timestamp: December 16, 2019, 12:27:39 pm
content: Quote from: Fraser on December 16, 2019, 12:05:38 amMy favourite toolQuote from: all_repair on December 16, 2019, 02:32:38 amUse soldered wires on the traces you are inspecting in order to eradicate probe pressure resistance problems

author: fcb
author_rank: Super Contributor
timestamp: December 16, 2019, 01:36:04 pm
content: When I was designing the probe tips for our V/I tester (sharp stainless steel), we did some research into pressure vs. tip shape. You certainly want a sharp tip to penetrate soldermask (if probing the tracks directly), but if it is too sharp you can easily 'puncture' the copper foil track, then you get some really weird results.Toneohms are sensitive to very small deviations in resistance. Check your tips for oxidation and you might find a slightly more rounded tip better.

author: Shock
author_rank: Super Contributor
timestamp: December 16, 2019, 09:38:57 pm
content: I own two of those HP 547A Current Tracers, the second one was meant to be a probe but was a tracer. They are very cool tools, the price has gone through the roof on them though. I also have an HP 546A Logic Pulser, HP 545A Logic Probe and the HP 10529A Logic Comparator which is all part of that set, useful for vintage logic.Adjustable curve tracers can be also be used for circuit testing, capacitor leakage testing, finding shorts etc. How far they cross over into the functionality of equipment like Huntron Trackers which also do component testing, I'd have to look into.

author: aqibi2000
author_rank: Regular Contributor
timestamp: December 18, 2019, 12:48:54 pm
content: Quote from: 3roomlab on December 16, 2019, 05:26:55 pmCan you reference the DIY Current probesThanks

author: Ghull07
author_rank: Newbie
timestamp: December 27, 2019, 09:20:01 am
content: I’m surprised I didn’t see it mentioned in this thread, And I apologize if I’m mistaken.There is a very similar device to the Tone-Ohm.It’s called the “leak-seeker 89” by “electronic design specialists” (EDS). It Was designed by Dave Migga 20 or 30 years ago. I’ve recently built one, and I am very impressed. It may very well replace my polar toneOhm devices that have been on my bench for the past few years.It’s very intuitive, very accurate, and super easy to use! EDS doesn’t sell them anymore, and they can’t be found used. But Dave at EDS offers parts kits, Including programmed chips.And “the eccentric workshop“ sells The PCB’s for $20, Original enclosure for $30, and even the original graphic decals for $10. All of it is the highest quality with no expense spared… so total build cost will be around $160. Very well worth it in my opinion!The guy from eccentric workshop worked really hard tracking down the original enclosures, which are made in America and very high quality. He designed the PCBs to great quality, and they drop effortlessly into the enclosure. It’s very obvious the PCB was designed to drop in that exact enclosure. it fits like a glove and makes Construction super fast! The decals are very high-quality vinyl, and have a UV protective top layer which should allow them to last a long time.I’m only a hobbyist, but my entire workbench is equipped with HP and TEK gear that I purchased “untested or broken”… And repaired myself. my experience and understanding is extremely lacking when compared to most of you guys… But I have disassembled, diagnosed, or repaired 50 or so pieces of “decent“ test gear in the past year. Mostly tek and HP stuff. So although Im inexperienced and not so knowledgeable… I have a basic understanding of what quality looks like...inside and out.And leakseeker has a good fit and finish, & a lot of thought has gone into design. The parts are all high-quality and everything is as it should be.If you search for the leak seeker 89 on YouTube, there’s a guy or who repairs video games and consoles… I don’t quite remember his name but he has a video demonstrating this device. He is very impressed with it. He didn’t really read the manual or practice with it first, so it’s a bit slow & repetitive… But you’ll get the general idea.I can tell you from experience, it took me about two hours to build the unit, and then about 30 minutes playing around with it, to become comfortable with the user interface. like I said it’s very intuitive. A child could use it. And it’s incredibly sensitive, But with the ability to adjust sensitivity and re-calibrate automatically.....in a heartbeat... without moving your hands or lifting the probe.The designer (Dave migga) also has a few videos on the design.Don’t get me wrong, I love my TONEOHM devices, my HP current tracer, my various curve tracers, my DE5000, The diy ESR multimeter adapter designed by the gentleman here on the forum, and of course my flir thermal camera. But the LEAKSEEKER was a welcome addition to my bench. And I’m sure you see the connection between all of those devices.... and my terrible grammar or writing style.... those devices make it easier for a dummy like myself, Who lacks great experience and understanding, but is learning quickly. And these various faultfinding tools feel like cheating… but help a beginner like myself to understand & see what’s happening in the circuit.Thank you for enduring my write up.I hope someone finds this helpful.

author: Shock
author_rank: Super Contributor
timestamp: December 27, 2019, 12:43:07 pm
content: Welcome to the forums and congrats on building your Leakseeker. I don't own one but I've known about the Leakseeker for a while now. From what I have seen in the past it works fairly similar to the Polar Toneohms but with auto ranging and has a simplified interface, with perhaps better resolution.It would be interesting to see a modern implementation of similar audible auto ranging short finder, would bring down the build cost a bit as well. Personally for me though I'd prefer to see the numerical value of the short at the same time as well as the LED bar and an optional audible tone.Unless I'm missing something about the Leakseeker signal or features a low voltage ohmmeter with good resolution or by supplying a small constant current into the short and measure mV will get a similar result if you pay close attention to the measurement increasing or decreasing.The other old EDS product the Cap Analyzer is similar in that it has a simplified interface, it tests DC resistance as well (which is handy) but otherwise I think the Bob Parkers ESR Meter design is better as it's a low cost kit.On the subject of low voltage ESR meters... since they need milliohm resolution to be usable for characterizing capacitor ESR they just happen to be good for finding low resistance shorts as well. A basic demonstration on how this works is in the below video featuring another cheap ESR kitset meter the ELV ESR1.

author: aqibi2000
author_rank: Regular Contributor
timestamp: December 29, 2019, 12:24:04 am
content: In terms of a cheap implementation of using a milli ohm meter just for comparison purposes of traces.This is an excellent implementation, with the addition of a small LED bar graph display and interpreting the ADC values this can be easily be adapter to some use.https://youtu.be/EYaIrRViKq0

author: harrimansat
author_rank: Regular Contributor
timestamp: January 10, 2021, 02:29:24 pm
content: Quote from: Fraser on February 03, 2018, 02:11:34 pmCan you please upload schematics?Thanks!Regards

author: kripton2035
author_rank: Super Contributor
timestamp: January 10, 2021, 02:33:54 pm
content: here it is

author: kripton2035
author_rank: Super Contributor
timestamp: January 10, 2021, 02:39:04 pm
content: Quote from: aqibi2000 on December 29, 2019, 12:24:04 amI just made a better one adding a display and a 4-wires probe to it. it now displays milliohms, and seems precise to half a milliohm. perfect when you dont want to wake up people in the next room ... with it I was able to detect a shorted capacitor among a bunch of parralel ones in a motherboard. nice. 2mΩ differences only. not detectable with sound only.

author: kripton2035
author_rank: Super Contributor
timestamp: January 10, 2021, 03:06:13 pm
content: some pictures of the device

author: harrimansat
author_rank: Regular Contributor
timestamp: January 10, 2021, 08:28:41 pm
content: Thanks!I like it, but for my experience two wires system to measure low impedances dont work very well, you need to make zero often. Are you using a constant curret? I prefer to inject current and use a microvolt meter, 4 wires.

author: kripton2035
author_rank: Super Contributor
timestamp: January 10, 2021, 09:12:11 pm
content: It is a shorty device, I used the same schematic. I only added an oled display, and 4 wires probes.I can't make a zero for the probes as the device detects them as zero.I will try to add a better ADC than the 10 bits of the arduino, and then may be able to detect the probes resistance.

author: kripton2035
author_rank: Super Contributor
timestamp: January 11, 2021, 03:28:50 pm
content: Quote from: Shock on December 27, 2019, 12:43:07 pmin fact I think they are not that good for short circuits. a DC milliohm meter is better. if you search for a short and there are capacitors between, it show as a short and it is not the short you're searching for.

author: Shock
author_rank: Super Contributor
timestamp: January 12, 2021, 01:48:57 am
content: Meh in circuit component testing (V-I Curve Tracer) for me none of this DCR rubbish.

author: kripton2035
author_rank: Super Contributor
timestamp: January 12, 2021, 07:16:07 am
content: just found another shorted ceramic capacitor in an apple time capsule. 2mΩ difference with the other caps . so easy now !

author: Shock
author_rank: Super Contributor
timestamp: January 12, 2021, 05:54:51 pm
content: Does it do anything special in software? What's the max measurement?

author: kripton2035
author_rank: Super Contributor
timestamp: January 12, 2021, 07:14:28 pm
content: I can read 0.6Ω but cannot read 0.7Ω, and down to 0.4mΩ (don't know the accuracy ! but it's not a problem I only need some scale for relative measurement)it is only the reading of the arduino ADC, and the display with some scale. the shorty amplifier gives some 13mV/mΩ at the arduino adc input.I will definitely try another better adc like a mcp3421 with 16 bits to see if there is a better possibility !I also added a change in the audio frequency response : I used a decreasing exponential response, 0 Ω = 4khz, 1Ω = 10hzthat way you can better hear the small resistances values.

author: harrimansat
author_rank: Regular Contributor
timestamp: January 30, 2021, 11:18:58 pm
content: Quote from: kripton2035 on January 12, 2021, 07:16:07 amWith your meter? Is an ESR meter? I thougth that it was a DC ohms meter.How it works?

author: kripton2035
author_rank: Super Contributor
timestamp: January 31, 2021, 09:04:00 am
content: it is a DC milli ohm meter. with an esr meter you search for caps with high esr resistance value, all caps must have low esr, so if you search for short it's not possible.with a DC milli ohm meter, I can find a shorted cap with others in parallel like on computer motherboards with 2mΩ difference.now I have added a mcp3421 adc, and I can have a stable measurment down to 0.1mΩ.I changed the amplification of the shorty op amp from 200 to 27, so that I can measure from 0.1mΩ to 4Ω (5 digits resolution)I also changed the opamp from mcp6041 to ad8628, I had too much offset voltage with the first one impossible to zero the probes.original shorty device :http://kripton2035.free.fr/Continuity%20Meters/continuity-short.html

author: harrimansat
author_rank: Regular Contributor
timestamp: January 31, 2021, 09:13:08 pm
content: thanks,I know, what I don´t understand is why you said "2mohms difference with the other caps", one cap is short and is resitive, but the others?

author: kripton2035
author_rank: Super Contributor
timestamp: January 31, 2021, 09:25:43 pm
content: you have a group of 20 tantalum smd caps in parallel at the output of a power rail. almost in every actual computer.one of the cap is dead short and prevents the power rail from working.you have to find it without removing all the caps one by one until you find the bad one.the faulty caps I have found are around 40mΩ. if you measure any of the cap with an ohmmeter you get 0.01Ω of resolution at best, and given that 1mm of copper is less than 1mΩ you can't find the bad capacitor.with my device, I get 2mΩ more reading on the cap next to the faulty one, and around 10mΩ more on the caps that are some cm away.so I only have to measure each group of caps, find the smallest ohm value, then find the smallest value inside that group and it's done.

author: harrimansat
author_rank: Regular Contributor
timestamp: January 31, 2021, 09:59:39 pm
content: Thanks for your explanation!The last board that I fix with shorted capacitors, had ten tatanilum in parallel next to CPU, apple mac pro, one of them very shorted, with 2 Amp it did not heat. With two probe needels connected to a differential amplifier, I find out that I can measure which capacitor is conducting meassuring the drop voltage in smd cap lead lenght, aprox 1mm., injecting 2A DC in DC railIn one photo you can see the drop voltage, moving de needle up and down through capacitor lead.300uV at 2A, 0.15 milliohms at capacitor lead???I used a tektronix 7000 series diferential amplifier, 7A22

author: kripton2035
author_rank: Super Contributor
timestamp: February 02, 2021, 09:45:15 pm
content: https://www.youtube.com/watch?v=4F6QNSpWTossmall video I just made with my device in action. more to come.

author: kripton2035
author_rank: Super Contributor
timestamp: February 03, 2021, 05:30:39 pm
content: another video showing the resistance of a soldier rollerhttps://youtu.be/8mYyr9uKpFU

author: harrimansat
author_rank: Regular Contributor
timestamp: February 03, 2021, 05:46:01 pm
content: Thanks, I want to make one!, do you have schematics and firmware?The only thing that I don´t like is that you need to hold tight against the circuit to measure well low resistors.

author: kripton2035
author_rank: Super Contributor
timestamp: February 03, 2021, 07:07:30 pm
content: I just started a new thread for it here :https://www.eevblog.com/forum/testgear/finding-short-on-motherboards-with-a-shorty-(with-display)/new/#newwith a new video showing how to find shorted capacitor

author: kripton2035
author_rank: Super Contributor
timestamp: February 03, 2021, 07:12:41 pm
content: Quote from: harrimansat on February 03, 2021, 05:46:01 pmwill share this when they are cleaned.yes if you want stable reading, you have to be quite strong in holding the probes, you could use some kelvin clips and be lighter with it.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 01, 2021, 12:20:44 pm
content: WOW, this is wonderful. thank you for all that you have done to share the knowledge.May I ask you the resister in the current probe is connected to the shield wire? and there are only 2 wires in there, correct? how far from the tip of the current probe would you say is the Inductor placed?so below is my story with the toneohm.I purchased a toneohm 950 about 8 months ago. Polar here in the US wants over $700 for probes of all 3 setups.that's about how much I spend on the 950. I was not going to spend that much more on Probes only.I had seen on ebay, pics of items (ebay-claric239) was selling, a toneohm 950 in the background, which was not for sale. so I massaged him to get info on its probes. This guy went all out, sent pictures and measured them for me. if you are looking for electronics check him out on ebay.I think 850 and 950 current probes are the same but the 850 is the current probe by itself and the 950 has the drive source with it on the same jack.ebay-claric239, did say it is an Inductor measured 220 uH and 10ohms resistance at the DIN pins. and your pictures explains it.I started making my probes last week. Needle probes was really easy and it works really good.the current tracer is work in progress. I have gone through a couple so far. on my last one I made an inductor in house with really tiny wire .004 inch, I didn't know there is a resister in lines. so, I wound enough wire to give me 10 ohm, about 12 feet. it works and is very directional. but I can use a smaller one, lol. the next version will be smaller. got to order an inductor and a resister.the 950 also has the drive source voltage variable up to 550mvdc. it has the needle probes, current probes and the Planer probes.the needle probes: voltage, current and resistance can be traced.with the non contact current tracer: well it says it.I don't think the Planer function on the toneohm 950 is going to of much use to me, for now.thank you for the info and pics.

author: fcb
author_rank: Super Contributor
timestamp: March 01, 2021, 01:22:31 pm
content: Got a mint 950 here with all the probes, etc.. shout/PM if you need any technical info.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 01, 2021, 09:41:13 pm
content: thank you very much. I wonder how the trace and the planer probes are wired at the DIN and inside the probe. Attached is what I been able to figure out on the machine side so far.

author: fcb
author_rank: Super Contributor
timestamp: March 01, 2021, 10:16:43 pm
content: Conectors are drawn from the backside (solderside) of the cable mounted connector.Hope this helps.

author: BobBeBob
author_rank: Regular Contributor
timestamp: March 10, 2021, 08:03:26 am
content: Hi, was wondering on the pictures of the current probel DIN connector and the 1 Ohm resister. is the resistor connected to the shielding cable of the coaxial cable?