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.
No worries. Maybe someone else on the forum will enlighten me if a lock in amplifier makes sense for microohm measurements :)
That is the HP current tracer probe that I have :-+
An 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.
Nice done. That is funny, I have done almost the same thing http://www.pa4tim.nl/?p=4207 (http://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.
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
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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.
3. 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 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
Yep, I have the standard 850 (non A) service manual and schematics.
I will send once I have your email
Fraser
If you do not have a PolarCare contract there is an admin fee of GBP 50 for electronic copies of operator manuals and GBP 495 for service manuals.
Caius,
I have sent you the 850 user manual as well.
Fraser
QuoteIf you do not have a PolarCare contract there is an admin fee of GBP 50 for electronic copies of operator manuals and GBP 495 for service manuals.
Did you read that on their website, what a joke.
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.
Fraser
Select the CURRENT TRACE mode and plug in the current trace probe. Connect the DRIVE SOURCE leads to a 10 ohm resistor.
Using an oscilloscope set to 20mV/div and 10uS/div monitor the voltage appearing across the probe. This is available on the back of the DIN socket between the centre pin and the pin with the coax braid.
Adjust R78 for maximum amplitude sine wave (typically 100mV to 102mV) with the current probe placed next to the DRIVE SOURCE lead and aligned for maximum signal.
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:QuoteSelect the CURRENT TRACE mode and plug in the current trace probe. Connect the DRIVE SOURCE leads to a 10 ohm resistor.
Using an oscilloscope set to 20mV/div and 10uS/div monitor the voltage appearing across the probe. This is available on the back of the DIN socket between the centre pin and the pin with the coax braid.
Adjust R78 for maximum amplitude sine wave (typically 100mV to 120mV) with the current probe placed next to the DRIVE SOURCE lead and aligned for maximum signal.
gives me at best a signal of about 20mV pp that roughly resembles a sine wave.
Any suggestions?
Thanks
Dave
The price of the probes you require for a 700 is:
ACC114 - £86.55 plus VAT and P&P £8.06
I have several Polar and Huntron V/I tracers in the lab 8)My favourite tool ;D
As you say, very useful :-+
Fraser
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.
seeing this thread reminds me of something i read 2 days ago
i dug it again and here it is
https://www.edn.com/electronics-blogs/the-emc-blog/4462331/Trace-ESD-current-paths-with-the-HP-547A (https://www.edn.com/electronics-blogs/the-emc-blog/4462331/Trace-ESD-current-paths-with-the-HP-547A)
(https://m.eet.com/media/1313729/Wyatt_ESD_current_fig1_2640x757.jpg)
HP547A
the entire circuit is inside the "pen", amazing idea for something made in 70s
i also saw many DIY spin offs on the webs
I will upload the 850A schematics as they may show the difference in the probe input circuits.
Fraser
In terms of a cheap implementation of using a milli ohm meter just for comparison purposes of traces.I 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.
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
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.in 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.
just found another shorted ceramic capacitor in an apple time capsule. 2mΩ difference with the other caps . so easy now !
Thanks, I want to make one!, do you have schematics and firmware?will share this when they are cleaned.
The only thing that I don´t like is that you need to hold tight against the circuit to measure well low resistors.