#131 

Mine is an older unit that doesn't have that functionality. Instead there's "DC-AC-Output" the last one of which just capacitively couples the input signal.

@ SIXSTRING63 Good to hear you developed an interest in Electronics. I developed mine when I was two years old by sticking my mothers crotchet needle into the AC Mains power-point live terminal. >. and LIVEd .. and I remember being thrown across the room. At age 8 my mothers brother (an Electronics Engineer was teaching me TV and Radio repair and to drive his Hillman Minx. That was in 1958. By the end of 1969 I graduated with a degrees in Electronics Engineering and Electro-Mechanical Engineering whilst then working fro PHILIPS.My then mentor, a very hard task-master made my head hurt, and I could have strangled him, though he was tough I never forgot what he taught me. He is still alive today, I see him often as he resides within 15 minutes drive from my home, and we have been friends for decades. I can recommend for you: EEVblog CHANNEL: ru-vid.com/show-UC2DjFE7Xf11URZqWBigcVOQ EEVblog Main Web Site: www.eevblog.com 2nd EEVblog Channel: ru-vid.com I have known Dave for decades also as we were both then members of TETIA -Television and Electronic Trades Institute Australia TESA - Television and Electronic Service Association

DeniskaNYC w

Yes, those Peak Atlas tests look really nice - I've been thinking about picking one up.

Oops, just spotted the next video you produced.

Very good point - and something worth checking out on the meter you intend to use for this purpose.

It uses a pair of C cells in series.

Looks like an ordinary general purpose NPN silicon transistor. Should be fine in your application with a properly designed circuit.

w2aew thank you for replying sir,.. I learned that transistor is a diode from this video sir... planning to watch other videos.. I just learned that electronic is interesting and found out late,.. I'm currently 41.. and God bless there's people like you share the knowledge.. thank you

Given that's an old Germanium PNP transistor, I'd expect leakage currents of a few hundred microamps.

Can you please make a video going over that?

Sounds like a failure to me. Base-emitter short.

w2aew Ok, thanks. And great video as always!

Sss Ttt I think this will depend a bit on the particular transistor type, so it might not be a reliable way to determine the terminals.

It might be that the emmiter region being heavily doped (rich in electrons for an npn transistor) creates a stronger electric field, this being seen as an increase of a few milivolts.

The emitter-base will always be higher than the base-collector reading for bi-polar transistors!!

It is possible that your meter has the reverse polarity on the test leads when in resistance measurement mode. You can verify this with a 2nd meter. Also, validate your measurements on multiple transistors to be sure.

That is because the guy is WRONG ! What he is explaining is ONLY if you have a Diode mode on your meter! Then the meter puts CURRENT through the transistor. If you just use ohms it is the reverse!

i got a different answer on SE. Something to do with 'Traditional analogue meters were reversed'. electronics.stackexchange.com/a/340108/65001

This is what I stated. Some analog meters are reversed polarity when in resistance (ohms) mode, some are not.

+Kennynva T. All bipolar transistors will work (poorly) when connected backwards (swap collector and emitter).

so you will get a reading when C and E is reversed on a germanium trany...thanks.

1. Bipolar transistors do have a pair of PN junctions, but they aren't really operating as two diodes. The base-emitter junction does operate like a diode and is forward biased when the transistor is ON. The base-collection junction is usually reverse biased un normal "linear" operation. It only gets forward biased with the transistor is saturated, such as in a switch application. 2. Bipolar transistors can, and do, rectify AC if the base-emitter junction is turned off during part of the AC cycle. This is exactly what happens in a Class B or Class C amplifier. In Class A, the transistor is bias so that the peaks of the AC aren't sufficient to overcome the forward bias of the base-emitter, so the transistor remains in the linear region.

@@w2aew If a diode doesn't have an DC bias voltage it will rectify an AC waveform but if you apply DC bias voltage until the AC waveform positive and negative cycles can pass through the Diode without getting clipped is the linear region of the diode. The difference between a diode and transistor is that when the AC waveform is passing through the diode is doesn't get amplify or increase in current gain. When an AC waveform passing through a transistor is increase the current and voltage of the AC signal. The transistor has something inside it beside a diode to make it increase the current and voltage of AC signals.

@@waynegram8907 Yes, of course. The base-emitter bias controls how much current flows from collector to emitter.

Nearly all silicon bipolar transistors will show between 500mV and 900mV. Anything lower than 500mV may indicate a shorted transistor, or possibly a Germanium transistor. Anything over 1V probably indicates a problem. If the readings are acceptable, these are signs that the transistor is *probably* OK, but there are failure modes that won't show up with this simple test (high leakage, beta degradation, high-voltage breakdown, etc.).

@@w2aew thanks for the explanation 😃. There is an other thing i'm sitting with....does a transistor has TWO- or THREE reading? I have a Hometheatersystem with a subwoofer issue. It goes into protection mode. I removed some main transistors and checked them with a DMM. The A1941/A940 and the C5198/C2073 give me two readings. But the L7805CV/L7815CV and L7915 CV give me three readings.....🤷🏽

@@tajlingchin2553 The first four devices are likely 2SA1941/2SA940 and 2SC5198/2SC2073 which are all silicon bipolar transistors. However, the last three parts are actually 3-terminal voltage regulators. The L7805CV is a +5V voltage regulator, and the L7815CV and L7915CV are +15V and -15V voltage regulators respectively. These can't be testing like a bipolar transistor.

@@w2aew thanks for the explanation. I've learned something new 😃

@@w2aew i did some more researches on the circuitboard and saw that the contactors of the relay (that steers the Subwoofer one side and the Center speaker on the other side) are burnt and glued together......

+Kennynva T. In general - apply a DC bias across the collector-emitter or drain-source with the base/gate biased off, and measure the current that flows.

+w2aew I see that heathkit for sale..and think I can get it for like 18$ the IT 18.

I have the Micronta dynamic checker now..but dont know how to check the leakage..I am using or checking germanium transis..now..form an old Harmon Kardon stereo..the radio has AM and plays fine but ZERO on FM...not a sound, no bodys home..

Or you can go modern at look at items like this: www.ebay.co.uk/itm/Peak-Atlas-DCA55-Atlas-Semiconductor-Component-Analyser-/112052577165?hash=item1a16daa38d:g:likAAOSwRgJXgitg or perhaps below (which does lot more): www.ebay.co.uk/itm/172225104646

If you just heard they can be damaged easily, you better look it up again. With the exception of them being more sensitive to ESD, you have to do really stupid stuff to kill them. Since they are voltage controlled devices they are way easier to test then the current controlled bipolars.

In-circuit testing can not always give you reliable results because of the unknown influence of other components in the circuit. Unless you know the schematic and then know what to expect from the remaining connected components, in-circuit test can only sometimes give you an indication of a gross failure (open or short).

@w2aew I am testing a relay and on the power supply side I get the 12vdc...all is good there...but the other side of relay I am seeing 6vdc...I am thinking there is an issue with the NPN transistor....any specific tests I can do? This is all over my head but I'm trying my best to comprehend it. I was told to short the base to ground so the transistor is not functioning at all and should not be conducting collector to emitter...if I do this I should see the 12vdc at the collector side of the relay coil...if I don't see 12vdc and I see something lower then it confirms the transistor is bad...is this correct?

@@macknumber9 Yes, as long as there is nothing else connected to that end of the relay coil that could be pulling current through it.

@w2aew yeah nothing else is connected....if I see 12vdc doing this test then what would you test next? The actual base voltage reading while in operation? I would expect to see .7v or higher at the base...if I see less then the transistor would not be at fault but possibly the transistor is not getting the right voltage because of anything before it? Bad resistor etc

@@macknumber9 Measure base-emitter voltage when "on", should be about 0.6 to 0.7V or so. Is there any resistor between emitter and ground?