Any old Pro’s here still use an Analogue Meter when testing semiconductor junctions?

[tvtech]

Hi All

Calling on the likes of Audioguru, Nigel and others who have been in the Electronic repair game for many years.

A discussion for seasoned repair Tech’s only. I want to hear what you have to say.

Newbies….this thread is NOT for you.. It will probably confuse you more…

Cheers
TV TECH

 

[mvs sarma]

i was in Indian telecom hardware servicing for nearly 35 years. let us discuss .

 

[ronsimpson]

Mostly I have digital meters. Most of the analog meters have died.
I like analog meters if the signal is unstable. You can see an analog meter "shake" while a digital meter may be unreadable.

For testing semiconductors I like meters (new meters) that read forward voltage drop not resistance. A diode resistance of 8 ohms does not tell me much. At 1mA a forward voltage drop of 0.6 = silicon, 0.35 volts = Schottky, 0.95 = high voltage.

 

[Reloadron]

I still use a Simpson 260 on a regular basis as well as a Simpson 269. The one older 260 (I have a few) must be 40 years old.

Ron

 

[Bob Scott]

Yes, I used to test diodes and transistors every day using a VOM. The VOMs I used were switched to RX1 resistance mode. If I clipped the black lead to the base of a known good NPN transistor, I would get a deflection of about half scale when touching the red lead to the emitter or collector, but no deflection with the leads reversed.
Note that if I switched to RX10 or RX100 mode, the deflection is still about half scale.
I then would test for E-C conductivity in both directions. There should be no deflection when checking resistance E-C or C-E.
In all of 25 years or so, I only found about 2 transistors that passed this test but were still bad.

Notice that in these tests show that the VOM actually has a positive voltage on the black lead with respect to the red lead when in resistance mode.

Note that the transistor must be removed from the circuit for these tests. If testing a PNP transistor, conduction between B-E and B-C will show opposite direction conductivity.

 

[BrownOut]

i don't own an analog meter. Haven't for many years. The only time I wish I still had one is when I'm looking for a very slowly changing signal, like when I'm trying to figure out why the turn signal won't light on my boat trailer. Digital meters are worthless for such measurements.

 

[audioguru]

I have used digital multimeters for many years.

 

[RichTheDude]

I'm not too old, but I prefer using my old Avo model 8 as an ammeter when powering up boards for the first time (assuming I do not have access to my lab PSU) - just becuase I find an analogue meter allows for me to monitor the rate of change of a variable a lot easier, my my digital meter usually reads nonsense whilst it is autoranging (quite a lengthy process!).

 

[JimB]

In the old days when I used to repair stuff for a living, if I had to test for a faulty junction in a diode or transistor, I would get out an analogue meter to do that task even if I was using a digital meter for the rest of the faultfinding process.
Nowadays to only faultfinding I do is in my own workshop where I use a digital meter.
That meter has a diode test position which I find works quite well for finding faulty junctions.

I do still have a couple of analogue meters, a rather battered AVO model 7 which was given to me many years ago, and a small Japanese meter dating from about 1970 when it would have cost about £1.50. Both of these meters are out in the garage somewhere, I use them occasionally when working out there on one of my cars or some other stuff.
Many years ago I worked as a computer maintenance guy at an oil terminal, the telemetry outstations around the terminal used a multiplex technique to read digital inputs from limit switches and such like, the little £1.50 meter was very good at displaying the pulses from the multiplexer so I could tell whether the switch was open or closed.
The instrument guys would blame the computer because a valve indication was not correct.
Two probelms, they did not understand how the inputs to the telemetry worked, and their nice expensive Fluke DVMs did not stand a chance of seeing the half second pulse from the mux, and were gobsmacked that my toy meter could.
(Sorry guys, there is nothing wrong with the computer, get out in the rain and snow and fix the limit switches on the valve!)

Analogue meters are good for adjusting things, such as when tuning for a maximum or minimum, but over the years I have developed an eye for using a digital meter to do the same thing, not easy but it can be done.

JimB

 

[Dean Huster]

Just remember that early semiconductors and early analog meters didn't play well together. Many older VOMs used higher voltage batteries for their higher resistance ranges. For example, the Triplettt 630 used a 30v battery. Newer VOMs use either 9v or 7.5v for their higher ranges. The higer voltages could damage some early germanium transistors that may have had lower reverse voltae specs. Most ohmmeters, DMMs included, have higher current available through the probes on the lowest resistance ranges, sometimes getting into the hundreds of milliamps. Keep this in mind when probing on sensitive semiconductors.

 

[debe]

Been repairing electronics for over 40yrs now & still use analogue meters for testing transistors & any voltage thats unstable. Also use Digital when necessary.

 

[Diver300]

I haven't used an analogue meter in years. Although the first digital meters were very poor, I find that the new ones are reasonably quick, especially if they have a bar graph. Also, having a diode test function, which is basically an ohmmeter but reading voltage drop directly, is a good way of testing diodes and NPN and PNP transistors.

 

[Reloadron]

Just remember that early semiconductors and early analog meters didn't play well together. Many older VOMs used higher voltage batteries for their higher resistance ranges. For example, the Triplettt 630 used a 30v battery. Newer VOMs use either 9v or 7.5v for their higher ranges. The higer voltages could damage some early germanium transistors that may have had lower reverse voltae specs. Most ohmmeters, DMMs included, have higher current available through the probes on the lowest resistance ranges, sometimes getting into the hundreds of milliamps. Keep this in mind when probing on sensitive semiconductors.

Dean makes a good point. My Simpson 269 uses a 22.5 volt battery as well as 1.5 volt D cell. Great meter but pain in the ass battery.

Ron

 

[tvtech]

I'm not too old, but I prefer using my old Avo model 8 as an ammeter when powering up boards for the first time (assuming I do not have access to my lab PSU) - just becuase I find an analogue meter allows for me to monitor the rate of change of a variable a lot easier, my my digital meter usually reads nonsense whilst it is autoranging (quite a lengthy process!).

I find that to be a valuable Analogue attribute too. When a TV is tripping, you can see a visual indication on an Analogue meter....whilst a Digital just shows a slowish, meaningless Bar graph and senseless numbers numbers on it's display.

Analogue shows what's actually happening with a QUICKLY moving needle/pointer.

Cheers

 

[Dean Huster]

There isn't a digital meter in the world that's worth a crap for peaking or nulling a circuit, bargraph or not. Unless you have a higher-end meter that samples hundreds of times per second, the bargraph doesn't respond quickly enough. A bargraph display on a DMM doesn't resolve to the precision of the actual numerical readout, so you can't really find the true peak or null using the bargraph alone. And tracking a digital display while trying to peak or null is nearly impossible. Those changing, flashing digits require some kind of a savant to interpret quickly enough to know which direction to tweak the circuit.

I can adjust a variable power supply to exactly 5v ±0.05v faster with a VOM than I can a DMM.

Analog meters, slide rules, analog clocks. The younger you are, the more you either hate them, don't know how to use/read them or don't even know what they are.

 

[mvs sarma]

......Notice that in these tests show that the VOM actually has a positive voltage on the black lead with respect to the red lead when in resistance mode.......

always positive goes into the red or positive socket.
In Ohms range, the power is from inside battery
if positive has to go in at V/O/A socket , it has to come out from "common" socket
thus we con imagine the black wire as positive , in Ohms ranges.
we need not specifically change the leads, i suppose. also some Analog multimeters used to supply a small accessory , a plug with a dual connections. one is direct to socket and other from the same pin but with a resistance.
It was used as aid for testing transistors' gain parameter .

 

[colin55]

I have just finished writing an eBook on Testing Components and everything everyone has said has confirmed my writings, that you need both an analogue and digital meter when servicing, testing and designing circuits and equipment.
The biggest skill is knowing when to use what.

 

[KeepItSimpleStupid]

How many lives did the Simson 260 have? I don't know how many versions there were. Then, there was there 260-II series.

While we are on the topic of analog vs digital, lets add car instruments:

My take on the above:
tach: for the driver, analog. For the troubleshooter: Both
speedometer: I'm not sure. I've seen both on a car. I've driven a recent Prius and Infinity, but I forget what kind of speedometer it had.

 

[Dean Huster]

How many lives did the Simson 260 have? I don't know how many versions there were. Then, there was there 260-II series.

The Simpson 260 began with the series I, then the II, III (those were all Roman numerals for the first three series), then the 4, 5, 6, 7 and 8. The 260 series 8 is the current offering for over $200 each. Within each series, you had things like the 5P, 5M, etc. The 5P offered electronic meter protection and the circuitry of the VOM differed from the 5. The 5M would have had a mirrored scale. Each "advance" in series changed the available functions, ranges, accuracy and reliability. The meter movements on the later series used taut-band suspension. Back-to-back diode meter protection was an early addition. Battery voltages have gone all over the place, most being either 6, 9 or 15 v with the requisite 1.5v "D" cell for the basic resistance ranges.

 

[mvs sarma]

I could locate one Simpson 260-8XPi. There used to be another Simpson model with wider scale and big enough, the connecting pins were to be inserted from sides.