Toa EPM 104 impedance meter

[anatech]

Hi All,
Does anyone have the calibration instructions for an impedance meter made by TOA? The model is EPM104, the ZM104 may be similar. Mine is reading high at as you go up the scale. I tested it against two resistor standards. It may be in spec, but I'd like to optimize it rather than make a correction graph.
Schematic would be cool. I could trace it but I'm lazy.

-Chris

[guidnesslondonn]

Re toa dm104

Dear anatech
I am fairly new to this site ,
but I wondered if you came across a setup and circuit diagram for the dm104 impedance meter?


Peter

[anatech]

Hi Peter,

I am fairly new to this site ,

Well then, Welcome to DiyAudio!

but I wondered if you came across a setup and circuit diagram for the dm104 impedance meter?

No, I am still looking for it. Sorry I couldn't help you with this.

-Chris

[Original Burnedfingers]

Chris,

I believe I have one of the meters in my service van. Does it have X's 1,10,100, and 1000 buttons and a cal button on it? The Toa is a very primitive inaccurate meter. It will only measure at 1K.

I tried about 15 years ago to get Toa to send me out some information on the meter and they wouldn't do so. I ended up calibrating the meter using a Sencore impedance meter with loads verified by the Sencore. There is a pot for every range. Using plain resistors doesn't work well. Use a transformer with a speaker attached (plain 70volt speaker of commercial variety). I will call Toa today and see if they will send me some cal information on it.

[anatech]

Hi Joe,
Thanks, you're very kind! Is a schematic available?

I did attempt to calibrate the meter myself using fixed resistors and did manage to improve it.

The Toa is a very primitive inaccurate meter.

The big problem is that the readings vary with battery voltage! It is a handy little beast and allows easier tracing and troubleshooting.

When you are looking at an amp rack (or four), it allows for very quick troubleshooting. It's accurate enough for that - just!

-Chris

[Audi O]

OK, so I know that this thread was started over 6 years ago & is probably no longer of interest to the original posters!......(but...)

I found this thread whilst searching for an answer to the same question, "how to calibrate my (similar) ZM-104". I could see that there are 5 preset potentiometers inside the meter which most likely are there in order to facilitate calibration, but I was reluctant to start adjusting them without some reassurance from another source. In particular, I needed to know which 3 of the 5 pots were used to adjust the 3 switchable ranges.

I got my hopes up towards the end of this thread, only to find that, disappointingly, no-one posted back with any info - so my trawl through the vast depths of the internet for an answer continued!

After wading through numerous sites which either just sold the meter, or reproduced the irrelevant but rather useful application sheet written by Syn-Aud-Con & found on the TOA website;

http://www.toaelectronics.com/downlo...SAC_ZM-104.pdf

I eventually struck gold & found the zm-104 service manual, which contains a circuit diagram &, in section 4, the much sought after calibration instructions.

In case anyone else, like me, comes upon this thread looking for the calibration info, here is where I found it. The manual is free, & the download link is towards the bottom of the page. Enjoy!

[Original Burnedfingers]

It doesn't download for me.

[Audi O]

Originally Posted by Original Burnedfingers

It doesn't download for me.

Strange. It works fine for me, & I also notice that it has been downloaded a couple of times since I last posted here, so I assume that others have had no trouble. I could have posted the direct download link here, but the webmaster may not like it, so I just linked to their webpage.

Just to be sure you are doing it right....

Right-click on the text "To download the file, please, click here !". Then click "Save Target/Link As".

Any more problems let me know, & I'll sort out something else.

[anatech]

Hi Audi O,
Thank you for that. I really like the accompanying article you ran across.

I ended up calibrating my unit via a trial and error method. I got it much closer than it was, but I'm never comfortable unless I can use the factory procedure. One thing I did notice is that the calibration is affected by the battery voltage. I confirmed this using a variable power supply instead of batteries. What this means is that the EPM 104 is an approximate reading device, so don't assume any great accuracy from it. It does a fantastic job of tracing PA speaker lines and showing improperly loaded amplifiers. That is far more common than you want to know about (overloaded amps).

I stopped looking after I had mine set up, so thank you very much for posting the manual.

Hi O.B.F.,
Downloads fine. The manual is at TOA ZM 104 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics

-Chris

[Audi O]

You're welcome, anatech.

Thanks for the tip on variation due to battery voltage. I'll be interested to see (probably after some testing) whether the 3 ranges become equally "inaccurate" as the voltage varies. That is, whether the 3 ranges still all give the same (inaccurate) reading, or whether 1 range becomes more inaccurate than another. It seems that a similar inaccuracy between all the ranges would be easier to remember & make allowances for, as the batteries become weaker.

I also have an Adastra digital audio impedance meter. I find this easier to use because it has additional features like a large illuminated display, & a reading-lock etc. It's main limitation for me has been the lack of sufficient audio output power, needed when I use it as a quick audio source at the head-end, to test the location & correct working of speakers connected to a large installation. They are hard to hear, particularly in a noisy environment (construction site or pub, for example).

The TOA ZM-104 was recommended to me as a much better meter, so I got this meter second-hand. The only downside to this cheap purchase was that I immediately noticed that 1 of the 3 ranges was giving a completely different reading to the other 2 - hence the need for calibration!