10 Ampere D.C analog panel instrument repair
This panel instrument below belongs to my good friend George. He removed it from a salvaged power supply along with a volt meter of the same manufacturer. Having myself seen at its back side an HC marking, I guess that it is a Hung Chang product (of Korean origin) but I am not quite sure about it.
George told me that the instrument’s indication is always much less than the real current flowing within it when it is in operation. This already started to trigger my curiosity. What could be wrong with that instrument?
I have in my mind cases having burned coil or bent/broken indicator needle pointer or non linear behavior of the instrument rendering it useless, but it’s first time I heard about such a case. So I took the instrument with me in order to investigate what was wrong with it.
When I ran the first test on it, I had a flowing current of 5A and indeed its indication was approximately 2,7A. Unfortunately, I was so much absorbed from its symptom trying to understand why this was happening, that I forgot to take a comparative photo of this first test (with another measuring instrument connected in series with it).
I started then to dismantle it. I removed the indication panel and its mechanism block. All I saw therein was what I expected to see.
There were: the internally installed shunt resistor made of approximately 2,5 cm long wire which was also about 2mm thick. (I didn’t take any exact measurements on mechanical dimensions as there was no reason for this). It had a Z shape, with its ends connected to the external terminals of the instrument. A short piece of very thin diameter cable in black color was connecting one terminal of the shunt directly to the instrument’s mechanism. Finally at the other end of the shunt there was a voltage dropping resistor made out of special thin wire, wound like a coil, connected there with its one end. Its appearance was very similar to an R.F. air cored coil. The other end of this wire was connected to the other terminal of the instrument’s coil mechanism.
So the instrument’s coil was connected in series with the voltage dropping resistor and then this set was in parallel connected to the shunt resistor.
Their connection is shown below:
The index containing relevant additional info refers to the analysis I did during its repair process. You will understand it by further reading…
As I could not understand what was going on, I started to analyze the circuit.
First of all I wanted to test the instrument itself as a stand alone mA meter and check first its behavior, especially if its indication was linear throughout its entire dynamic range, because it would be irreparable in case it revealed non linear behavior.
In order to do this, I removed the voltage dropping resistor from the circuit by desoldering its one end from the instrument’s coil mechanism. Then I used my Mastech 7020 analog multimeter as a current source for the test. I selected its Rx10Ω range, in which it gives a full scale output of 15mA.
You can see below the Ω ranges of this multimeter along with the full scale current (: namely when its output terminals are short circuited) provided to its test terminals per each selected range.
By the way, it is worth saying here that there is a good reason for avoiding to test any small signal diodes or transistors or even LEDs using the Rx1Ω range of an analog multimeter, as this can very likely destroy their silicon crystal.
My instrument gives an output current of 150mA in this range (as you can see in the photo above) and in general all analog instruments of the market give similar output currents in this range.
Another important fact as regards these instruments is that when measuring Ω, the negative terminal of the instrument is the positive pole of its internal test current source, whereas its positive terminal is the negative pole of the source. In other words we have polarity reversal at its test terminals.
This usually confuses beginners when testing semiconductor components as they (logically) think that they apply the test signal with its correct polarity and weirdly the P and N junctions, which practically are respectively the anode and cathode ends of the diode under test, are found to be in reverse arrangement within the component than the expected one and therefore this effect is causing them a lot of confusion. For this reason this effect should always be taken into account during relevant tests. Similarly, of course, P-N-P transistors look like being N-P-N and so on…
To avoid this confusion when testing semiconductors (instead of normal resistors where polarity of course doesn’t matter) you can simply reverse the connection of your probes to the multimeter terminals (that is, the red probe to be put to the black receptacle and the black probe to the red receptacle).
And finally here is a practical tip in order for you to protect the needle pointer of your precious analog multimeter when carrying it with you for the various testing tasks in the field.
During carrying it, you should always have preselected beforehand its lowest volts range (in other words its microampere range as shown in the above photo) having also its COM and V/Ω /A inputs short circuited together. In this way, the needle pointer will not move freely here and there any longer by the usual vibrations developed on the body of the instrument due to your walking or to the transportation means moving and the instrument will remain absolutely safe and immune to vibrations.
This trick is based on the fact that after doing all above the short circuit is applied directly to the terminals of the microampere meter of your multimeter and therefore it acts as an electrical brake. The effect is similar to your try to revolve the rotor of a short circuited permanent magnet D.C motor. You will realize that you cannot revolve it and you will feel the strong “braking” effect in your hand when you try it.
Back to our topic now. Having myself selected the 15 mA current source I connected on the negative terminal of the multimeter and in series with it the positive terminal of the D.U.T (= device under test). Its free negative terminal was then connected to one end of a 5KΩ linear trimmer potentiometer. The wiper of the potentiometer was preset to its maximum resistance and then connected to the plus terminal of a digital multimeter set to measure mA D.C (:20mA range). The free negative terminal of the digital multimeter was going directly to the free end (positive) of the analog mutlimeter and the circuit was already closed, ready for the test to start.
The connection is shown in the schematic below:
I started testing by gradually reducing the potentiometer’s resistance in order to see the current changes in the indicator panel of the D.U.T and compare them to the current flow indication of the digital instrument.
To make things easy for the linearity test, I chose to add before each next step of the procedure an amount of 0,65A to the value of the previous step, which represented 1A indication on its display.
Performing the test I created a table as shown below:
Now dividing each digitally indicated current by its respective analog indicated one, as shown below, the resulting values were found equal to each other:
0,65/1=1,3/2=1,95/3=2,6/4=3,25/5=3,99/6=4,55/7=5,2/8=5,85/9=6,5/10=0,65
This means that the above table is an absolutely convincing proof that the mA meter as a stand alone instrument was in perfect operating condition.
Right afterwards I measured the voltage drop on the D.U.T terminals, when its indication was in full scale. It was 32mV referenced to 6,5mA flowing through the D.U.T, when it was indicating 10A.
At this point I was “stuck” indeed! The rest of the circuit was only wire resistances that never change in value. In case of excessive current flow through them they simply get burned. But this is practically impossible for an amps meter to happen.
A shunt resistor can withstand an enormous amount of current before being destroyed in this way and the thin-wire voltage dropping resistor would need that enormous current flow through the shunt to get destroyed along with the moving coil of the instrument as well.
The information I had available so far from the above “road map”, was that I had a 6,5mA D.C meter, with its moving coil having a resistance of:
Rinstr= U/I → R= 32mV/6,5mA=4,92mΩ → 5mΩ (rounded up)
Then I connected a 5W car-lamp in series with the shunt and (being to approximately near to 12V output from my PSU) I measured 2,5mV for 0,36A current flow. This means again that the value of the shunt resistor was:
Rsh= U/I → R= 2,5mV/360mA=6,94mΩ → 7mΩ (rounded up)
This in turn means that with a current flow of 10A through the shunt resistor there will be a voltage development at its ends of the order of:
U=R*I=7mΩ * 10A=70mV
Therefore for a full scale display of the analog instrument needing 32mV, there are in excess:
70mV-32mV= 38mV to be dropped
For this drop a dropping resistor is needed, having a value of:
Rvd= U/I → R= 38mV/6,5mA=5,84Ω
I verified that this value was correct with that coiled resistor therein, after an additional Ω measurement on it.
So everything was perfect but the instrument was faulty…Very weird indeed…
I began thinking about it all over again. Then I remembered that when I desoldered the coiled resistor from the instrument’s terminal and trying to pull it in order to see its connection of the other end, this left me with the feeling that on its way from the shunt’s terminal up to the instrument’s coil assembly it was somewhere stuck.
Seeking a logical explanation for all of this weird effect, I removed again completely the coil assembly of the instrument and put it under a magnifying lens, supplying also plenty of light to it. Then I noticed that at approximately the middle of the shunt resistor’s body there was a stain…
It was now clear to me what happened with this instrument.
The hand- made voltage dropping resistor was put inside there in a wrong way, right from the manufacturing date of this instrument. Some turns of it were touching the shunt resistor’s body. When the shunt was repeatedly heated enough over time because of the flowing current through it, little by little this heat destroyed the insulation of the voltage dropping resistor at their touching point and the electrical effect of this short circuit was the equivalent of having a shunt installed therein having almost the half value than the needed one for these 10A of full scale display. This short circuited condition would need almost double current flow in order to drive the moving coil to its full scale…
That’s why the original indication I had in my first test, before doing anything else with it, was approximately 2,7A for an actual current flow of 5A exactly.
Note as well that this instrument, when working at 10A current flow, develops a power drop on it of the order of:
P = I2 * R = 102A * 7mΩ = 0,7W
And this loss manifests itself always as heat on the shunt’s body. Over time, even being of such a small magnitude, this thermal loss is nevertheless capable of causing such a weird failure… The case I had in front of my eyes was simply a proof of this argument to be actually true.
You can see the comparative measurements, after the repair, in the pictures below:
Of course many of the readers may say that such an effort for a cheap analog panel instrument was not worth repairing it, but I am already very well aware of this fact.
The point is that on one hand I just love these instruments because I was grown up using them and I feel very sad realizing that in our days they tend to disappear rapidly. George on the other hand had done so much of hand-work for its mounting in the front panel of his power supply while he could not find the same instrument all over Athens and he was desperate about it.
And this was the right time for a good friend to get involved and give a helpful hand! Despite the time I spent with it, this was a good refreshing exercise for me and hopefully a good tutorial for many of you the readers of this article.
I hope you enjoyed this weird but nevertheless real case of failure and its repair…
This article was prepared for you by Paris Azis from Athens-Greece. He is 59 years old and has more than 30 years’ experience in electronics repairs, both in consumer and industrial electronics. He started as a hobbyist at the age of 12 years and ended his professional carrier as a senior electronics technician. He has been a specialist in the entire range of consumer electronics repairs (: valve radio and BW TV receivers, transistorized color CRT TV, audio amps, reel and cassette tape recorders, telephone answering and telefax devices, electric irons, MW cooking devices e.t.c) working in his early stages at the official service departments of National-Panasonic first and JVC afterwards, at their premises in Athens.
Then he joined the telecoms industry, working for 20 years as field supporting technician in the sector of DMRs (: Digital Microwave Radio transmission stations), ending his carrier with this subject. Now he is a hobbyist again!
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Note: You can check out his previous repair article below:
https://www.jestineyong.com/netvil-dvb-t-receiver-no-power-on-repair/
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g wells
November 2, 2015 at 10:41 am
you are one smart man.
Paris Azis
November 3, 2015 at 12:43 am
Thank you very much ”g wells”. Anyway I believe that anyone involved with electronics’ repairs is smart, even only for this reason alone.
Perhaps what makes the difference in my case (and for sure I am not alone) is that I just love this job. In my humble opinion this is the unique basic prerequisite to succeed in this job. Next to this one must also have more qualities such as a good theoretical background but always those qualities which refer to the temper of the technician are the prevailing ones…If patience is not there along with strong will to restore the original function of a dead device or if imagination is missing during the troubleshooting procedure or in other words if one sees no challenge during troubleshooting but some dollars hidden somewhere therein, then “the game is over”…
At least this was, is and will be the way I see electronics’ repairs.
Thanks again!
Anwar Shiekh
November 2, 2015 at 10:46 am
Figuring things out is a dying art; these days people just swap out faulty parts till the problem is gone.
Paris Azis
November 3, 2015 at 1:04 am
Come on Anwar! Please stop mourning and enjoy the happiness of a repair! We all know that the world is moving forward, but we try to adapt ourselves to the changes this brings.
Finally as long as we are alive, nothing is dead yet!
Moreover “swapping out faulty (?) parts till the problem is gone” is not a method at all. It is a chaotic procedure instead, not to be adopted from technicians, and has all those characteristics of “the wheel of fortune”. Whoever technician works in this way is simply gambling. But gambling with electronics is at least unnatural if not dangerous for both the person who plays the role of the supposed technician and for the device under repair as well. Chances are for it to be rendered irreparable after such a repair “method”.
Greetings!
Abdul
November 2, 2015 at 11:18 am
Thank you Azis.
A good tutorial and a smart man.
Paris Azis
November 3, 2015 at 1:06 am
Thank you too Abdul for your supporting comment.
Greetings!
Mark
November 2, 2015 at 11:19 am
Hey Paris,
Well done in figuring it all out. I will be honest - some of it was over my head, but I'm sure if I read the article again, I could understand your diagnosis.
I totally agree, we live in a throwaway world and repairers like ourselves (I am not claiming to be at your level - I am just a humble hobbyist), don't like to see things thrown away, but would rather spend hours on something just for the satisfaction of repairing the unit. It's a good feeling when you see something come to life again.
I have been in the automotive trade for about 35 years and I still get a buzz when I have followed a diagnostic path and the vehicle fires up again! I have even created a YouTube channel designed on making complex diagnosis simple - just for the fun of it.
I admire guys like yourselves that obviously have had years of experience that you can pass onto hobbyists like myself.
Keep up with the good work!
Paris Azis
November 3, 2015 at 1:33 am
Hello Mark
When our thoughts coincide, of course this makes me happy! Yes, if there is something you didn’t understand I also believe that you will find the answer you seek if you just read the article again. I believe that I have all the necessary explanations in its text.
But in case you have a “cloudy” picture about anything therein just feel free to ask me.
And yes, you are right about that feeling of mine. I cannot resist a repair, especially in cases I consider a shame to be thrown away for such minor reasons as a burned transistor for example, or even worse for a burned fuse. And this last example I have seen it many times in the last years.
This is consumerism madness to me and nothing more. Who needs a new TV every six months and for what reason exactly? And worse than that, those people who would possibly answer me “I do, just because…”, how healthy are they mentally? And these are some of the critical questions which of course I am not the proper professional to answer… We must show some respect to the new generations to come I think and not keep acting like being left ourselves in a permanent childhood…
Thank you for your supporting and encouraging comment.
Best Regards
Mark
November 3, 2015 at 9:51 am
Hey Paris,
Thanks for your feedback. I will definitely re-read the article when I have some quiet time so that I can get it through the thick grey matter. A lot of it is getting a good understanding of Mr Ohms law and how it relates to components and how they react to one another.
Recently, my wife suggested (we'll call it that...) that I get rid of some of the clutter (units needing repair). I made her happy by gutting a microwave oven that I picked up from the tip a few months ago and used the magnetron for another repair. I didn't have the heart to throw the whole thing away - so the components are in the garage. At least it looks a little tidier in the Lab!
Just like you, I can't bare to see things thrown away for the sake of a simple repair. I also hate that a component can get the better of me and spend many hours searching for the elusive fault.
The younger generation just don't seem to get our passion (obsession). Maybe when they are older?
Who knows....
Good to hear from you and keep up with the excellent articles!
Paris Azis
November 3, 2015 at 4:46 pm
Hi Mark
Although our wives are right about a tidy home (one way or another they are the queens of the home…) we, on the other hand, need some space of our own for working with electronics. And this is where some times the “star war” starts…
Don’t bother, because you are not alone in this story…
That part of hating the culprit component (I passed through this as well) has long ago turned in my mind in a soaring curiosity to find it through further non-stop troubleshooting until I have it laying down on my bench.
As for the new generation…I have many questions unanswered yet, plus some reservations, but first this is natural between generations and moreover I prefer to be optimist about all of these…
Best Regards
Mark
November 5, 2015 at 5:18 am
Hey Paris,
I work part time as an Automotive Teacher at a local college. At the moment I am teaching students that have almost finished their apprenticeships the subject of Diagnostics. I was a little surprised that they mostly have no real concept of following a logical diagnostic path! Some of them even said they were scared of the term Diagnostics. Fortunately, during the course, I was able to teach them different strategies, logical thought process and how to hunger for the answer. For several weeks before we started this topic, I told them of the vehicles that I have introduced faults into and of course they just made random guesses, but it made them curious to find the fault and now I believe they have the process in mind when doing diagnostics. It is something that you have to learn from somewhere and have a passion for finding the fault and the buzz you get when you finally complete the repair and operate the unit.
On the wife front, my wife tends not to come into my lab, since it usually just results in a long sigh and a shaking of her head in disbelief. But I believe that I will win her over one day....... However, when something goes wrong, I am the first one she calls on for my skills, so that must say something. To do some work, men must have a 'man cave' where they can do there repairs and not feel they must tidy up at all costs 🙂
She's actually not that bad - I just like teasing her - that's how she has managed to put up with me for 32 years!
Paris Azis
November 5, 2015 at 5:47 pm
Hey Mark
Your feedback is opening an entire new chapter of discussion, but for space economy I will not refer to extensive details…Moreover I need to say some things, which I feel in advance that in case they are misconceived, they will mark me as a sovinist and this is what I want in the same time to avoid…Anyway read this only if you please or else ignore it.
What I want to tell you? I merely want to give you a tiny sample of how the Greek language is an unbelievable tool for both problems’ solving and correct thinking…
Let’s take a review in your last text. I see therein the Greek terms “auto”-motive, “diagnostics”, “logical diagnostic”, “strategies”, “logical” thought…
Now let me “analyze” them and you will “automatically” understand much more than you know up to now, and I ask you in advance to pass this knowledge to your students.
“Auto” the first part of “automotive”, means “by itself”. Thus the car is “something that moves by itself” or else “automatically”, again with the same meaning.
“Diagnosis”, composed from “dia+gnosis”. The first part states the means of acting for achieving the second part. “Dia” means “through” and “gnosis” is “knowledge”.
Can you realize now what exactly you are doing when performing a diagnosis? You are trying to find out what is true (the quintessence of knowledge) through your own knowledge. Does this simplify the overall picture in your mind?
“Logical”…This refers directly to the father of the scientific term “Logic”, Aristotle.
It expresses all those rules of thinking so that we are standing on a solid basis for what is correct.
Here is a simple and practical example of it: “if the sky is heavily cloudy and the temperature drops, I will take my umbrella with me”.
I believe that you can already distinguish the AND gate your mind process similar thoughts in order for you to be safe…
“Strategy”…This is a military term. It originally comes from the word “stratos” meaning “army” and specifically it refers to the rank of a General, who is the “stratigos”, “the leader of the army”. Well, “strategy” is “the planning of the leader of the army”, the so called “strategic plan” in order to win the war, not only a battle. Is it clear enough? Is it “didactic” for your students?
In conclusion, no matter if one believes it or not, my language helps me as a most powerful tool in finding solutions to arising problems by just thinking.
I have written all above just because it happened to me as well to teach people in the past…
And according to my father’s belief (he was a high school teacher when being alive) “teaching is shaping human souls”…Perhaps nothing is more respectful to that in life I believe.
On the wife front…I also believe that our wives behave in general similarly. And it seems that we are irreplaceable in two things. First in carrying those heavy bags from supermarket to home and last to carry the equally heavy bags of home garbage to the bin we throw them in!!
Best Regards
Mark
November 6, 2015 at 5:16 am
Hey Paris,
I fully agree! Believe it or not, what you have stated is EXACTLY how I start my Diagnostics course. I start with the origins of the word. I generally start my courses this way. Sounds like you, your dad and me would enjoy a long discussion, maybe ending in circumlocution!
I guess that is why I love diagnostics as well. The opportunity to think something through. To start, progress and arrive at a conclusion. Starting with something that is beyond logical thinking and then to come to a satisfactory end.
In fact, the motto of my YouTube channel is 'Making the Complex Simple'.
On the wife front, we are partners for life. I do most of the heavy lifting, but I still get away with too much....maybe. Still, as you say, most wives fall in the same category & aren't too keen on us having our space, our messy 'man cave'. But that's why you build them with a door!
Enjoyed our chat.
Cheers
Paris Azis
November 6, 2015 at 3:27 pm
I enjoyed too Mark. I wish you the best for your future plans...
peter wang
November 17, 2015 at 9:52 pm
Hi Guys,
Like most hobbyists our little room or lab is what I call an organized chaos, a perfect workplace where we know where things are supposed to be.The purpose why we keep so much junk around is for the precious parts we salvage from them to make other stuff work. The wife just do not comprehend. Great Articles. Always an inspiration for simple hobbyist like me.
Paris Azis
November 28, 2015 at 7:46 pm
Hi Peter
Please excuse the delay to answer you. And yes, this “organized chaos” is exactly what women hate. And this happens just because they cannot understand the reason you refer to…Anyway when the term “woman” becomes “wife” things are getting harder for us but fortunately, working with electronics, we have a lot of patience and understanding about their point of view!
Greetings
Gerald
November 2, 2015 at 12:15 pm
Hi Paris,
Interesting story and well written as usual. I fully support the time spent to repair this kind of instrument. I also grew using them and they are still very useful, and beautiful too...
The idea of using the analog multi-meter as a low current source is great. I never thought about it and keep it in the back of my mind.
Thanks for sharing and Best Regards,
Gerald
Paris Azis
November 3, 2015 at 1:39 am
Thank you Gerald for your warm and supporting comment.
The idea about the analog multimeter is simply a product of good and timely imagination. That’s why I insist on it!
Greetings
Anthony
November 2, 2015 at 2:35 pm
Hi Paris,
Another great article from you ! I agree with Mark that even though it may not be worth repairing, it's still good to work our brains and try to fix something if it's at all possible because this keeps our minds sharp ! Thank you again for taking the time to prepare this article and share it with us all here because it is also educational and fascinating to benefit from all your years of experience in electronics! I always enjoy your articles and feel privileged that you take the time to prepare them for us.
Best Regards
Paris Azis
November 3, 2015 at 1:43 am
Thank you Anthony for all your support and encouragement to me.
Best Regards
Muftah
November 2, 2015 at 3:00 pm
Hi Paris,
very informative post, thanks a lot.
I have problem with small transformer with unknown secondary voltage, I need your help... the only information available is the resistance of the secondary side witch is consist of 4 outputs. is it possible to know the voltage with this resistance? 2 outputs with 22 ohm and 2 outputs with 6 ohm.
input 220v,the transformer is Italian with this information on it : ENCO srl
ETI-1065-B S7R97
Paris Azis
November 3, 2015 at 3:13 am
Hello Muftah
Unfortunately d.c resistance is not much of help in this case. It is a valuable info in repairs of electric motors where the experienced technicians always compare the d.c resistances of their (same to each other) windings in order for them to come to correct conclusions about their health. In the same way they also assess the temperature of the windings when testing the motors. But talking about transformers I think that this info is useless. At least I have never read anything about their use in transformers with the exception of losses calculations etc, but it’s irrelevant to winding voltages calculations.
You could possibly use this info (theoretically) only if all the windings had used the same wire, but this is impossible for a transformer…
With your reference to four outputs and the resistance values I understand that it has two independed secondary windings. Please confirm if this is correct. Next tell me please what you mean by stating “a problem” with it. Is it in proper working condition or its primary winding is already burned out? Can you also give me the dimensions of its core area? This will tell us about its V.A rating, which is a good starting point…
Because in such a case, I am afraid you are forced to work in a similar way as I did. Namely dismantle it first removing its core laminations and then count the turns of its windings and measure their diameters in order to rewind it. On the other hand you have nothing to lose in such a case. The damage is already done…
Best Regards
Albert van Bemmelen
November 2, 2015 at 3:22 pm
Thanks Paris! I never heard about the special analog Mastech 7020 meter you used to measure the DC resistance of this 10A analog problem meter, and the fact that it gives currents up to 150mA set to the X1 Ohm scale onto the connected DUT. You took a lot of time to test if the 10A Analog meter still was linear. I myself could have used my MW1008 meter in this given example. That meter gives the Z, X and R value of any attached impedance. I think that your article describes that in the end you found the answer of the defect by just analyzing the single components involved (component level repair). In a way that is what you did in your previous article were you completely dismantled a transformer. It kind of proves that you do save a lot of time if you divide any repair into the smallest pieces it consists of. And also how a small weak component in the device chain can cause a big complicated electronic problem.
Paris Azis
November 3, 2015 at 2:16 am
Hello Albert
I think that there is a confusion in your comment. My analog multimeter has not anything special on it. All analog meters work in a similar way. I din’t measure directly the shunt resistor of the amps meter with it. I only used it as a current source for testing the mA meter within it.
The linearity test, yes, it took me some time but this is normal in such cases…And no, unfortunately, you cannot use your instrument in this case. Impedance will lead you nowhere. D.C resistances is what it counts here.
And yes, you know now my method! First step “analysis” that is breakind the problem down in pieces that can be checked sequentially in a logical order. Then comes “synthesis” which is the reverse procedure of “analysis”. We articulate the entire structure of the logic conclusions of each previously checked step and finally we have on hand the final and overall solution. It is all a systematic way of thinking that brings positive results.
Arbitrarily thinking (:without any logic) on the contrary is the best way to wander in a chaos… I humbly believe…
And according to my experience, major troubles have almost always, or at least as a rule, minor causes…There are only a few exceptions to this rule…
Best Regards
Albert van Bemmelen
November 4, 2015 at 2:22 am
Yes I know Paris. Thanks for your reply. Of course all analog meters with X1, X10 Ohm setting do give a high current. But since you and Robert both do love to use still such old devices and I never saw an analog meter that looked like a modern digital one, like your Mastech 7020 meter does, I just mentioned this.
The special digital MW1008 meter I often use is also a LCR meter that easily is able to find any DC Low Ohm (R) value including any Inductance or Capacitance (X) on a component level. And gives also the total Impedance being the Z value, (everything according to the laws of Pythagoras). And also on multiple frequencies. The MW1008 also uses special coax testcables which eliminates measuring faults because of the used testcables themselfs. Every testcable therefore consists out of two coax cables parallel with on each end a testclip. After finding the Culprit component this way probably also would have shown the 10A Analog meter under test functioning without any error. And the need for the linear test would have passed. And also the high meter currents would have been omitted this way. I Just think that measuring the Analog way is old and can be avoided! But according to the dislike point on my Post above I've said too much already? Although I do like analog meters just like analog clocks, because digital displays tend to confuse people more. And saving this 10 A meter is a good thing! I am happy for your friend!
Albert van Bemmelen
November 4, 2015 at 4:29 pm
By-the-way: Paris, the MW1008 also adds this little gem, the measuring bridge also knows a transformer measurement in which the Transformer ratio and the phase relationship is determined from a voltage measurement.
Jestine Yong
November 4, 2015 at 4:56 pm
Hi Albert,
This seems to be a good meter. I have checked the spec and max test frequency was only 25 khz. The standard meter test frequency for checking e-caps in the market is 100khz. Do you see any different in the result when checking the e-caps with 25 Khz?
Thanks.
Jestine
Albert van Bemmelen
November 4, 2015 at 10:13 pm
I checked my MESR-100 ESR results against my MW1008 (PIC microprocessor controlled!). My MESR-100 gives a very unstable 0.019 Ohm resistance that fluctuates up to a rising 0.046 Ohm. My MW1008 meter is very stable and gives a -0.005 Ohm resistance at 100 Hz, up to a -0.006 or -0.007 Ohm serie resistance at 25KHz (slightly fluctuating ESR).
My PIC version still has a little BUG that I found in the PIC Menu that the Author apparently never noticed and would fix if I were to send in my little PIC board in for a reprogram at Shipping cost to France. I never bothered. The meter seems to be a kind of a clone from an existing HP LCR meter if I am correct. My MW1008 was bought as a kit. But couldn't exactly be calibrated according to the Kit instructions. It failed at one or two calibrations that also never passed the exact values given. Nevertheless it is probably my most exact calibrated digital LCR meter and gives total impedance Z out of the square root of (-R ^2 + X^2). The testcable is the Kelvin sort of precise measuring method. By the way: I used a 1000 uF 16V e-cap in my test of both meters.
Jestine Yong
November 4, 2015 at 10:35 pm
HI Albert,
Thanks for the good explanation.
Jestine
Albert van Bemmelen
November 4, 2015 at 10:48 pm
I did a second test because my Kelvin cables on the MW1008 could have been wrongly connected. Because the R resistance is positive when the LD,HD and the LS and HS Kelvin test clips are correctly connected on the component under test. But because the coax cables are a bit stiff an error is easy made. I now used a 680 uF 16V e-cap. It gave 0.094 Ohm on my MESR-100. And it showed 0.234 Ohm at 100 Hz on my MW1008. And at 1 KHz it gave an R of 0.160 Ohm that became 0.139 Ohm at 25 KHz. The values on my MW 1008 were always very stable but even dislocating or touching the MESR-100 cables seemed to influence the resulting value.
Jestine Yong
November 4, 2015 at 10:55 pm
HI Albert,
Thanks again for the test. Can we conclude that we can test an e-cap using 25 Khz but expect the result in ohm would be a little bit higher?
Jestine
Albert van Bemmelen
November 5, 2015 at 4:30 am
Hi Jestine. I think that both meters actually give about the Xc value times 10 at a given frequentie? Or is that a coïncidence ? You see at 25 KHz Xc (or the reactance) of the 680 uF e-cap should be about 9.361 milli Ohm. And the ESR was 0.094 on the MESR-100 (which is about 10 times the Xc value). And about 0.139 Ohm on my MW 1008. But of course both meters have different testfrequencies. At 25 KHz my MW1008 meter gives a ESR value that is 1.48 times higher as the MESR-100 ESR value does on the same e-cap Under test. Which should correspond with a factor 14.8 times the Xc the Reactance value. And knowing this compared with the Good capacitor list as printed on the Blue ESR Meter, the ESR value at 16V should be just under about 0.110 Ohm. And to be more sure I naturally also tested another 680uF 16V e-cap on the Blue ESR tester and it gave a value of 0.24 Ohm. So it means the MW1008 is closer to the truth because the MESR-100 deviates the most from 2 other meters.
Paris Azis
November 5, 2015 at 1:47 am
Hi Albert
Your comments are always welcome. That dislike point is not mine for sure! I will take a look in the web about your instrument. It seems to be interesting, although I believe it fits R&D laboratories…
Thanks again and my best regards!
Albert van Bemmelen
November 5, 2015 at 4:30 pm
Thanks Paris, Although it looks like a R & D kind of device, as a DIY kit it was just about like affordable. But because of Calibration errors that occured while following the exact instructions, I would advise anyone interested to choose for the completely build and Calibrated MW1008. And because I found also an irritating Bug in the PIC Controlled Menu of the previous kit version, I think that the French firm selling these Kits made some unprofessional errors that in the end could have hurt their profits! (meaning less sold kits). Adding the fact that they also keep the PIC Firmware completely to themselfs, it could be a buzzkill. But since also the MESR-100 did cost a significantly $68 too, which is about less of a third of the MW1008P, it all is a matter of opinion. On this link they sell a completely new P model of the MW1008 that looks great! :
http://www.ormelabs.com/en/?page_id=144
And if they did their homework the old bugs should be gone too!
vishesh
November 2, 2015 at 3:59 pm
Yes the effort is worth.
not because you saved 1 Analog meter being discarded, more for the patience you have exhibited. these analog meters are the basics of today's Digital ones.
the process of fault finding is simple superb, hats off to you sir.
Paris Azis
November 3, 2015 at 2:19 am
Hello vishesh
Thank you for your warm and supporting comment. Our thoughts coincide!
Best Regards
Suranga Electronics
November 2, 2015 at 5:54 pm
you are super Engineer...
Paris Azis
November 3, 2015 at 2:23 am
Hello Suranga
Considering all those cockroaches and lizards you fight with you are superior I think!
Best Regards
Paulo Brites
November 2, 2015 at 6:39 pm
Congratulations Mr.Paris for your good explanation.
This kind of repair is make was proud when we complete the job.
I also love analogic instrument. The reason should be obvious I am 70 years old and got my first electronic course in 1963.
Paris Azis
November 3, 2015 at 2:30 am
Hello Paulo
Thank you for your warm and encouraging comment. Considering your age, your comment is of much higher value to me. Yes, this is my driving feeling, exactly as you describe it. You have my full respect Sir.
Best Regards
George
November 2, 2015 at 7:31 pm
Paris,
Analog meters are pieces of art in comparison to today's digital displays. I am glad to see someone feels the same way by going to the trouble to repair this device and keep it working. Great job!
George
Paris Azis
November 3, 2015 at 2:40 am
Best Regards
Thank you George. I fully agree with you. Analog meters are really pieces of art…It’s a pity that they rapidly disappear nowadays…And always this magic pair of words is hidden behind this…”cost reduction”…or “high cost”, name it as you wish anyway. It simply doesn’t matter…
Best Regards
Robert Calk
November 11, 2015 at 12:39 am
Good job, Paris. Thanks to people believing analog VOM's are obsolete, I was able to get a BK Precision 114A in mint condition very cheap! The simple fact that many overlook is that the VOM with the X10K has the 9V battery that added with the 2 AA batteries gives the meter more voltage than most DMM's. Plus, I supposed nostalgia has something to do with it also.
Paris Azis
November 28, 2015 at 7:37 pm
Hello Robert
Please excuse my delay to answer you. In fact it seems to be not so easy to follow up all of these comments in our published articles!
Perhaps the analog instruments are obsolete in our digital era, nevertheless they are in closer relation to the nature of the (analog of course) signals they measure. I personally prefer to see the sudden jumps of a needle pointer when I observe an audio signal instead of the bar graph of a digital multimeter. Those classical VU meters in audio amplifiers were irreplaceable I think.
I also agree with the observation about the X10K Ohms range. Perhaps there are still applications for it which never came in my thoughts up to now.
As for “nostalgia”, I will simply give you the original translation of it and you will be filled with much more relevant feelings. So, “nostalgia” is “the sweet pain that memories bring you, making you to realize that you are a foreigner in some place and forcing you to get back where you belong to”. It comes from “nostos” (= return) and “algos” (=pain, distress, etc). Its original meaning refers to “the sickness of the immigrants”.
My greetings to you
Robert Calk
November 29, 2015 at 3:42 am
No problem. We Americans don't use the word that way - nostalgia is the happy longing for the old ways. Every tool has it's uses.
Humberto
November 2, 2015 at 11:08 pm
Hi Paris, good explanations of your repair, as usual. Congrats.
Paris Azis
November 3, 2015 at 4:48 pm
Thank you Humberto.
Greetings!
Yogesh Panchal
November 2, 2015 at 11:08 pm
Paris, thanks for sharing informative article.
Paris Azis
November 3, 2015 at 4:49 pm
Thank you too Yogesh!
Best Regards
Parasuraman S
November 3, 2015 at 6:03 am
Vow! That is a lot of info! A very good effort, indeed! I remember my days when I worked in British Physical Laboratories (BPL) handling these analogue panel meters and planning its production as per pending orders!
When compared to the satisfaction we get out of such odd jobs, the efforts we put in, however trivial thing it might be, is inexpressible!
Best of luck!
Paris Azis
November 3, 2015 at 4:59 pm
Hello Parasuraman
It makes me also happy to realize that my article refreshed your memory bringing back sweet moments of the past…All of us need such moments to reappear some times…I believe that this works as a reference basis for us to see where we were in the past and then think or plan about how we can go to our targeted destination in the future…
And I fully agree about that satisfaction matter…
Best Regards
Ulises Aguilar Pazzani
November 3, 2015 at 12:25 pm
Mr Paris there is no words for this repair Your good , keep it up , learning from You Sir
Paris Azis
November 3, 2015 at 5:02 pm
Best Regards
Thank you very much Ulises (and you keep on learning)!
Best Regards
mta muhyadeen
November 3, 2015 at 6:30 pm
Hi Paris,
Interesting story and well written as usual. I fully support the time spent to repair this kind of instrument. I also grew using them and they are still very useful, and beautiful too...
The idea of using the analog multi-meter as a low current source is great. I never thought about it and keep it in the back of my mind.
Thanks for sharing and Best Regards,
Gerald
Paris Azis
November 3, 2015 at 11:58 pm
Hello mta muhyadeen
I understand that your thoughts are in absolute coincidence with those of Gerald’s!
In any case thank you too for your support.
Best Regards
Ulises Aguilar Pazzani
November 9, 2015 at 9:40 am
Sir MY respects for You , good explain
Paris Azis
November 9, 2015 at 10:13 pm
Thank you Ulises for your support.
Best Regards
sornruk
December 18, 2015 at 4:24 am
Wow !!! You be number one.
Paris Azis
March 25, 2016 at 2:13 am
Thank you, sornruk for your support.
Please excuse my long delay to answer you...
Best Regards