Toneohm 850A short finder by Polar Instruments - a look under the hood.

[Fraser]

Shock,

Phew !, I should have asked for £100 for the SM 

The 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

[caius]

Caius,

I have sent you the 850 user manual as well.

Fraser

Fraser, this is very kind from you, I was going to ask the operator manual as well but you read in my mind 
Within 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.

[caius]

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.

Did you read that on their website, what a joke.

Yeah, I have read it.it's ridiculous!

[Shock]

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.

[Fraser]

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

[caius]

Fraser, what  about the model 700?I have found one at good price.

[Fraser]

The Toneohm 700 is an excellent portable version of the 850. I own one of those as well  I have the user and service manuals for that model.

Fraser

[caius]

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.

[lukier]

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 price  The unit is perfectly fine except yellowish case with some stickers (retr0bright could help but I wouldn't bother to whiten the entire case).

[caius]

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

You were right, two of three secondary winding are broken near the pin, I attach picture.I'm going to resolder them.Stay tuned.

[Fraser]

Caius,

Yes, I have a collectors mentality to test equipment. I shall be downsizing soon 

I own the following models of Toneohm

550 Qty 2
580 Qty 2
700 Qty 1
850 Qty 1
850A Qty 2

I attach some pictures grabbed from the internet to show what they look like.

Fraser

[caius]

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.

[caius]

Now it's up and running.The culprit was the main transformer, most of the windings were interrupted.Many thanks to all for help! 

[Shock]

Reading of -4.2 milliohms, the short must be inside the Toneohm

[caius]

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!

[perdrix]

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:

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.

This gives me at best a signal of about 20mV pp that roughly resembles a sine wave. 

Any suggestions?

Thanks
Dave

[perdrix]

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:

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 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

[Fraser]

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

[perdrix]

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 500mV_pp into an open circuit and 360mV_pp across a 10 ohm resistor.

Dave

[Fraser]

Do you still need the Model 700 manuals, or have you now got them ?

Fraser

[perdrix]

I have a pretty scrappy scan of the user and service manuals but would appreciate having better ones.

Thanks
Dave

[Fraser]

I have the document archive PC back up and running so will send you what I have.

Fraser

[Fraser]

I have just uploaded the Toneohm 700 User Manual, Service Manual and Application manual to Filedropper........

http://www.filedropper.com/toneohm

These are the officially supplied PDF's from Polar when they use to offer such on their web site.

Enjoy 

Fraser

[perdrix]

Thank you

Dave

[perdrix]

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